Go for the Green

Home Improvement Projects with Conservation Ideals

Incorporating "green building" in your home improvement project is a double-edged sword well worth wielding.

Provided you are prepared for the extra leg work and higher up-front costs than those for conventional building, the pay-off is reduced energy and maintenance costs, increased home values and environmental protection.

"Green building" means building with sustainability, longevity and conservation in mind.



This deck is plastic — recycled plastic — and has a longer life than wood.

Rather than using materials that must be replaced in a relatively short period of time and techniques that gobble up energy, green building uses more durable, recycled materials, renewable products and less energy to manufacture materials. It also conserves resources during and after construction, avoids toxic materials and engages climate-and site-responsive design.

"Definitions for building green vary somewhat. Most would include a discussion of goals aimed at efficient use of land, enhancing energy efficiency, water conservation, indoor air quality and resource conservation," says Liza Bowles, President of the Upper Marlboro, Md.-based National Association of Home Builders Research Center.

For the past decade, the trend has focused on using alternative materials and techniques en masse in building new homes to get the most bang for the green building buck, but smaller home improvement jobs can benefit as well.

"You have less choice when doing remodeling. You are stuck with the foundation and the framing, but with everything from replacement roofing to window replacements, there are resources," says Tracy Mumma, a program specialist at the Center for Resourceful Building in Missoula, Mont.

NAHB's research center says green building benefits include:

• Lower operating costs. Homes requiring less heating and cooling and using less water have lower utility bills.
  
  
  
• Lower maintenance. More durable materials reduce upkeep and replacement costs.
  
  
  
• Improved environmental quality. Attention to, say, moisture control or using low-VOC (volatile organic compounds) paints can contribute to a healthier indoor environment and ultimately a better local environment.
  
  
  
• Increased value. Documented lower monthly utility bills and homes that perform better and longer, enjoy increased value.
  

Experts say virtually every home improvement project lends itself to green building.

"There are many degrees of "greenness" – from using low-VOC paints in your conventional, wood frame/sheet rock home to building with straw bale and earthen plaster," says Bill Christensen, founder of Austin, Texas-based Sustainable Sources, which helped make Austin a leader in the green building effort.

Green home improvements can include:

• No-VOC or low-VOC paints and finishes and less toxic adhesives.
  
  
  
• Ceramic tiles made from recycled windshield glass.
  
  "It looks like custom-made tile, so it'll have jagged corners, but when you are finished you'll have what you were looking for," says Leon A. Frechette, author of "Build Smarter With Alternative Materials" (Craftsman, $34.75), which offers green building techniques, materials and theory for more than a dozen housing components.
  
  
  
• Durable decking materials made from recycled plastic grocery bags, sawdust and pallet wood.
  
  "A lot of individuals are upset about keeping deck surfaces clean and free of flaking. This is a polymer, a maintenance-free product. You won't have to worry about staining and sealing," said Frechette.
  
  
  
• Carpeting and carpet padding spun from shredded plastic soda pop bottles. "You feel these things and they feels like cotton. It will blow your mind," said Frechette.
  
  
  
• Bamboo flooring that's harder than oak.
  
  "It can be harvested in four years, compared to 20 years or more for trees," says Christensen.
  
  
  
• A variety of shake roofing made of light-weight concrete; recycled polyvinyl chloride or steel; as well as a combination product made of wood fiber, fly ash and cement; all are designed to look like wood shake.
  

Unfortunately, the new products aren't always readily available, forcing consumers to seek out proven materials and contractors skilled in using them.

Green product manufacturers are often reluctant to emblazon their products with the recycled symbol and face the "made-from-garbage" stigma, says Frechette.

Home Depot, Lowes and other major retailers don't heavily stock green products because of their higher prices.

Contractors who are schooled in building green must grapple with local building codes that often aren't green-building inclusive.

"Get some type of education. There are books and Web sites promoting alternative materials. Contact manufacturers to get samples and check them out. Get references from contractors who have installed these products. Check the track record. Just because it's an alternative material doesn't mean it was designed for your geographical area.

Four Step Weatherization Guide

The (Re)Weatherization Sequence

Step 1: House Air Tightening and Systems Checkups

1. Duct sealing and insulation. If you have forced air ducts in your house, have them tested and sealed by a state certified duct-sealing contractor. Ducts should only be sealed with duct mastic, never with tape (Home Depot often carries duct mastic). While the duct sealers have their blower door set up, find out how leaky your house is, and where the leaks are. Consider installing additional return registers or pressure bypasses if you have a single return forced air duct system. After they are sealed, insulate the ducts to at least R11 (R25 is better), even if they already had an inch or two of insulation. If the system has air conditioning, put a vapor barrier on the outside of the duct insulation.
   
   
2. Air seal the house. Use caulking, spray foam, plywood, sheet metal, and weather-stripping, to seal places where air moves inside from outside, and also vertically through the house. Seal around windows and doors, seal the gaps around plumbing, wiring, mechanical, and chimney from underneath the house and from the attic. Sweep attic insulation aside, clean and foam the cracks where interior and exterior walls meet the ceiling. Cover the holes where plumbing drops through the floor under the bathtub and shower. Install outlet and switch cover plate gaskets. Remember that fiberglass does not stop airflow! A dense cellulose pack will reduce infiltration. Using a blower door makes airsealing faster and more effective.
   
   
   WARNING! Steps 1A and 1B. If you have any combustion appliances in your home, equipment that burns wood, pellets, gas, propane, oil, or kerosene, such as fireplace, woodstove, space heater, gas log, water heater, furnace, range or oven, etc., it is critical that you have a trained contractor perform a Worst Case Depressurization Test, or Combustion Appliance Zone Pressure Test to verify that the changes in the house have not created combustion gas backdrafting hazards. Combustion gas backdrafting can be fatal or cause long term health damage. An state certified duct sealing contractor can perform this test for you, and show you how to correct any hazards.
   
   
3. Ventilation and other systems checks. A blower door test will demonstrate how tight your house actually is, and where you may have missed a leak or two while airsealing. If your house tests below .35 air changes per hour (ACH), you should install fresh air vents as well as a high quality spot ventilation bathroom fan, or, ideally, an air-to-air heat exchanger to help maintain good indoor air quality. Install quiet bath fans and make sure they are properly vented outside through the roof or wall (see the Energy Outlet handout on bath fans). Install a range hood or verify that the existing fan vents to the outside in galvanized steel parts only. Make sure the dryer vent goes completely outside, in metal duct, not plastic. Now is the time to replace knob and tube wiring, add a grounding conductor, or otherwise upgrade your electrical system. Add phone or data lines. Check for adequate attic and crawlspace ventilation. Complete any structural repairs. Make sure water pipes are freeze-protected. Check for signs of water leakage around flashing at windows, doors, and dormers. Dry out that wet crawlspace with drains or a pump, and install a 6 mil plastic ground sheet.
   

Step 2: Insulation

Insulate the ceilings, floors, and walls of your house. Do uninsulated or low R-value areas first. Ultimately, you want all exterior components of the house fully insulated. Many houses are underinsulated, even if they have been “weatherized” in the past. Some contractors will attempt to persuade you that an attainable R-value is not “cost-effective”. This assertion is based on an obsolete set of assumptions.

The Insulation Rule of Thumb: There is no such thing as too much insulation! There may be technical or financial obstacles to installing more insulation, but there is no such thing as too much.

If you add insulation to the exterior (cool) side of a building surface, be sure unfaced insulation is used, so that the one and only vapor barrier remains next to the warm surface at the interior side of the building component. If the vapor barrier has been installed to the cold side, turn the insulation over or peel or slash the barrier. Often floor framing cavities are not completely filled, and can be added to. Additional floor insulation can be installed with wood furring or 16D nails that add depth to the framing, or with rigid foam sheets. Don’t forget to insulate cantilevered floors, or the rim joists, especially on multi-story homes. Vaulted ceilings often require rigid foam sheet insulation or added interior framing for fiberglass batts. Even insulated exterior walls can be improved by installing 1"-2" rigid foam sheets inside and re-sheetrocking. Use extruded polystyrene or polyiso foam, and foam and tape the joints for an excellent vapor barrier. Consult with the Energy Outlet for detailed insulation project assistance.

Step 3: Windows

Install new windows. Windows are last on the building shell list because they offer the least bang for the buck of any weatherization measure, and are usually the lowest priority in terms of actual heat loss. Exceptions to this rule include jalousie windows or windows that need expensive repairs. When you buy windows, specify these options: warm-edge glazing spacer, Low E glass (set up for a heating climate), krypton or argon gas fill. These glazing options will get you a window with a U-value close to .30 (lower U is better). Optimize the characteristics of the Low E coating by using soft-coat Low E on north and west facing windows, and hardcoat Low E on south and east facing windows. The choice of frame material is purely an aesthetic and cost question, since vinyl, composite, fiberglass, and wood frames perform about the same thermally. Existing wood frame windows can often be retrofitted with double-glazed replacement sash that come with new insert jambs, available from Kolbe and Kolbe, Marvin, and Pella. Old double-hung wood windows with weights can be replaced with larger windows if you extend the new windows into the area formerly taken up by the weight pockets. Excessively large window areas, especially if they don’t face south, should be sized down when windows are replaced. You may need overhangs, awnings, or rollup shades to keep the summer sun out. Rigid foam panels can be used as very effective interior nighttime window insulation.

Step 4: Heating Appliances

Install high efficiency home heating and water heating equipment, and maintain it properly.

Install the best Energy Star equipment, and you may qualify for an state income tax credit.

1. Sizing. As you tighten and insulate your home, the amount of heat your house requires to stay comfortable will decrease. Make sure your heating contractor does an ACCA Manual J Heat Loss Calculation to establish a heating and cooling load for your house as it will be when weatherization is complete. Size all new equipment to the new reduced heating and cooling loads.
2. Efficiency and Safety. Most pre-1990 propane, natural gas, or oil furnaces operate at less than 80% combustion efficiency, some as low as 60%! You can install a 90%+ efficient furnace or boiler and reduce your heating bill by an amount corresponding to the difference in efficiency between new and old heating units.
   
   WARNING! Atmospheric draft combustion appliances nearly always present the risk of backdrafting, especially if they are located indoors! Avoid using atmospheric draft appliances. Fan-forced or sealed combustion heating appliances are always safer and more efficient, and are essential for indoor installations. And, despite the fact that they are may be legal in your state, “Unvented” heating appliances should never be used indoors under any circumstances!!! (Unheated garages are not usually considered “indoors”)
   
   Heat pumps. Heat pumps allow you to improve the efficiency of an electric heating system, are available as ground source or air source models. Ground source heat pumps are amazingly efficient, but expensive to install. Ground source well systems are preferred over field systems. Energy Star air source heat pumps have an HSPF of at least 7.6, and SEER of at least 12. Air source heat pumps are available for ducted or ductless systems. Split ductless heat pump systems avoid expensive duct installation and heat loss, and are easier to retrofit.

Check with your local government for Energy Tax Credits and Business Energy Loans for installing high efficiency and renewable energy building systems. Your heating energy supplier will provide an energy audit of your home, and some incentives also.

Energy Efficient Housing Construction: Ventilation and Conservation

Ventilation

Air Leakage

Older homes rarely suffered from a lack of fresh air. Air leaking in through cracks and holes in older homes and poorly built new homes can allow the entire house air volume to change more than once every hour. Air also leaks in to replacing air which is used by the chimneys and exhaust appliances or through upper storey windows (because hot air rises). Energy efficient homes do not have such air leakage problems. Homes today can be built so airtight that the entire volume of the home would take many days to be replaced. This would, however, lead to poor indoor air quality causing stuffiness, indoor pollution, odour buildup and high humidity problems.

Natural Ventilation

Although energy efficient homes stay cooler in summer because of high insulation levels, natural ventilation should be provided with opening windows or screened doors. On one and one-half or two-storey homes, windows opening on different levels will promote natural ventilation by convection on warm summer days and nights. Openings on different sides of one-level homes will permit cross-ventilation. There are times ventilation may be required in the winter as well. Sunny warm winter days (with a low sun angle) may cause short overheating problems in a well-insulated, properly oriented home - a fast and easy solution is to simply open a window or two for a short period of time.

Mechanical Ventilation Systems

A much more reliable and effective approach to use in today's world of well insulated and air
sealed homes is some type of controlled mechanical ventilation system. With a mechanical ventilation system occupants are able to control the ventilation rate, and have the ability to keep air pollutant levels as low as possible while increasing oxygen levels and avoiding the problems associated with uncontrolled air leakage. There are a variety of systems available, from exhaust only types to continuous, balanced mechanical ventilation systems.

Balanced ventilation systems are recommended because they exhaust stale indoor air and replace it with an equal amount of fresh outside air, thereby preventing any pressure differences from occurring. These systems should be designed to exhaust warm, stale air from major pollutant sources, such as bathrooms, kitchens, hallways and laundry rooms, while distributing fresh incoming air equally throughout the rest of the house.

Balanced Mechanical Ventilation Systems

Non-Heat Recovery Systems are one type of balanced mechanical ventilation system. These systems use separate fans to exhaust stale house air and supply an equal amount of fresh outside air. This maintains the pressure balance within the house. It should be a system which exhausts and supplies air all over the home with separate ductwork or through a forced air system. Ventilation rates should be maintained between one quarter to one third air changes per hour (ACH).

Heat Recovery Ventilation Systems

Heat Recovery Systems are another example of a balanced mechanical ventilation system. They exhaust stale air and supply an equal amount of fresh air. The two streams of air are passed through the core of the heat exchanger, where heat from the exhaust air is passed to the cooler incoming air. Fresh air supplied to the rooms of the house has already been pre-heated, reducing the problems with cold drafts and the extra expense of pre-heating cold incoming air.

Since the stale, humid air that has to be exhausted contains heat, reclaiming some of that heat can reduce the energy loss while pre-heating cold incoming air. An air to air heat exchanger (also called a Heat Recovery Ventilator or HRV) is commonly used in energy efficient housing to extract heat from the outgoing air.

Currently available units are capable of extracting 70% to 80% of the heat from the exhausting air. Tying a heat exchanger into the return air duct of a forced-air heating system works well. The incoming fresh air is distributed evenly to all living spaces by the heating system duct work. An alternative for housing using non-forced air heating systems is to have the air-to-air heat exchanger separately ducted into each room. Either way the fresh air will mix well and, if a ventilation rate of one quarter to one third the total house volume is maintained each hour, humidity, odours and indoor air pollution will not be problems.

Drawing air from bathrooms through a heat exchanger instead of exhausting it outdoors also saves heating energy in winter months. As mentioned in the construction section 'Roofs and Ceilings', exhaust ducts should be vented down interior walls to the floor joist space where they could easily be attached to a heat exchanger. Excessively humid air can cause an ice buildup in a heat exchanger but most commercially made models have a defrost cycle to control ice buildup.

Because of potential grease and lint problems, range hoods or clothes dryers should not be exhausted through an air-to-air heat exchanger. Recirculating range hoods with good quality filters will eliminate having to exhaust air from that source.

Water Conservation

Water Use

The importance of conserving water relates in two ways to energy efficient housing. Energy is used to heat water so lowering hot water use saves energy. Energy is also used to gather, treat and supply water, so lowering total consumption will also save energy. Rates paid for urban water and sewage services are rapidly escalating to meet the energy costs of processing, supply and disposal. In a rural situation, lowering total water use means less wear and tear on pumping equipment, lower electrical costs, lower treatment costs and fewer sewage capacity problems.

Water Volume Conservation

Although a lot of energy is used to heat water, the bulk of the total water volume a home requires is used for flushing toilets. In the typical household the toilet accounts for 43% of water usage, showers and bathing use 29%, laundry and dishwashing 19%, drinking and cooking 5% and 4% for other (car washing, lawn watering, etc.) New 1.6 gallon (6 litre) toilets can reduce toilet water usage by 60 to 80% . Composting toilets are also available which use hardly any water at all. Water reduction devices such as tap aerators, flow restrictors and low volume showerheads also help reduce water usage when washing or showering. Common sense can be applied to find other ways of lowering water usage - habits changed, wastage reduced, etc. In areas where water shortages may occur through drought or an unpredictable (or expensive) supply, conservation is doubly important.

Domestic Water Heating

In an average home, a large percentage of the energy purchased is used for domestic hot water heating. Domestic water heaters can use electricity, natural gas, propane, wood, coal and even solar energy as a heat source/fuel. Gas burning and electric hot water tanks are available in tank (storage) types and tankless (demand) types. Standard gas-fired water heaters have seasonal efficiencies of 50% to 60%. More efficient gas units with electronic ignition, induced draft fans and improved heat exchangers offer efficiencies of 75 to 80% but cost more. Electric units are more efficient but electricity is more expensive than gas so on going operating costs are higher. Locating water heaters close to the points of use and insulating supply lines will help improve efficiency. Point-of-use electric and fuel fired units which are installed directly in the kitchen or bathrooms work well but flow rates (2 to 4 gallons per minute) are low. Some hot water heating systems (usually boilers or combined systems) can also be used to produce domestic hot water in companion hot water tanks.

Using hot water efficiently also relates to efficient appliance operation. The hot water tank temperature need only be set at 120° (50°). Most new dishwashers have electric heating elements to boost water temperatures. Only full loads of laundry or dishes should be washed. Water level controls in clothes washers should be utilized for smaller loads and cold or warm water can be used for many cycles. Hot water use can further be reduced by installing flow restricting devices such as tap aerators, flow restrictors and low volume showerheads.

Preheating the cold water supplied to the hot water heater is another way of lowering energy consumption. Preheating can be done with a dark coloured tank placed so as to be solar heated in a sunspace, greenhouse or in front of a south-facing window.

Gray water heat recovery systems which can preheat incoming cool water are also available but are not approved for usage in all areas.

Domestic solar water heating systems are a proven technology which can make a significant contribution to the hot water requirements of the average family. A wide variety of solar domestic hot water systems are available. Modern solar water heaters will now work when the outside temperature is well below freezing and are protected from overheating on hot, sunny days. Many models also have their own built-in, back-up heater which can meet all of a consumer's hot water needs - even when there is no sunshine.

Electrical

Electrical Energy Use

Electricity can account for one-third of the energy dollars a homeowner spends. The amount of energy may only be one-tenth of the total but, because electrical energy is more expensive per unit, it can be a significant part of your energy bill. Appliance operation and lighting accounts for most of the electrical consumption in the average home.

Lighting

The use of electric lighting is a necessity in cold climates because natural light is in short supply in the winter. However, lighting can be designed for efficiency. Matching light output to requirements, locating light sources properly and using efficient fixtures are all points to consider in lighting design and layout.

When planning the layout of spaces and rooms, consider the functions and place the lighting accordingly. Work areas require more intense light levels than relaxation areas. Individual lamps may work better than a single ceiling source in bedrooms. Use highly efficient fluorescent light sources in task areas (like the kitchen, laundry or workshop). Use timers, sensors and dimmer switches to add flexibility, safety and security to your system. When available, natural light should be utilized through proper window layout.

Exterior lighting should be carefully planned as well. Avoid an excess - but do maintain a safe level. The lighting intensity (and positioning) should be at an adequate level to prevent accidents. Motion detectors or timers can be used to turn lights on and off as required and can substantially reduce energy usage and operating costs.

Appliance Selection and Use

Appliances such as refrigerators, freezers, washers, dryers and stoves consume a large portion of the electricity you buy. Buyers of new major appliances should check for energy usage labels to help choose products which use less energy. Look for labels which state in kilowatt hours per month the amount of energy an appliance will consume under normal usage. Potential buyers can save money by checking energy consumption totals when comparing similar models of appliances.

Maintenance

Regular maintenance of the systems in an energy efficient home is the most important point in keeping that home energy efficient. All appliances and heating equipment will operate longer, have less problems, and use less energy if properly cared for. On a notepad, or in a small scribbler-type book, routine maintenance or service (as pointed out in appliance manuals) can be recorded. The date, type of service, costs involved, time taken, or any number of points can be noted. It then becomes a good reference and convenient reminder for routine maintenance. Some major maintenance points include:

• Heat distribution systems rely on an unimpeded movement of air. Keep duct work, fans and filters clean and make sure grilles, registers or convectors are not blocked by furniture or drapes.
  
  
  
  
• The heat source should be serviced frequently during the heating season. Furnace units require filter cleaning monthly, motor lubrication twice yearly and regular visual checks on the blower drive belt condition, tightness and alignment. Hot water systems, using a boiler, rely on a circulating pump which should be lubricated twice yearly. The venting pipes and chimney connections should also be checked periodically for tightness or any signs of leakage or rust spots.
  
  
  
  
• Wood space heaters or stoves should be checked periodically for tightness of connections and joints. As well, a thorough chimney cleaning is required periodically to reduce creosote deposit buildup. The frequency will depend on the type of wood burned and amount of use. You can monitor creosote deposits by occasionally looking in the chimney.
  
  
  
  
• If your home utilizes solar energy, keep south-facing glass clean, absorbing surfaces dusted and mass floors uncluttered. If any ducts, fans, vents or thermostats are incorporated to move passively heated air then keeping those parts clean and air flow unimpeded is important.
  
  
  
  
• Some energy efficient homes rely on window insulation to lower heat loss at night. Keep the edge seals clean on interior window insulation units. Regular lubrication of hinges, latches and operators may be required for exterior movable panels.
  
  
  
  
• The domestic hot water heater should be drained every two or three months to remove sediment from the tank. Proper water treatment and filtering, if the water supply is questionable, will help prevent scale or sediment formation in the hot water tank.
  
  
  
  
• Duct work used in ventilating the home should be kept clean. Dampers on exterior outlets should be adjusted so that closure is positive. Air-to-air heat exchangers should be cleaned regularly as should any auxiliary air filters installed in the system.
  
  
  
  
• Major cooking, storage and cleaning appliances will operate more efficiently and last much longer if regularly maintained and operated as specified in service manuals. Clean reflective surfaces on stoves, heat exchanger coils on fridges and freezers, and replace filters on a regular basis.
  
  
  
  
• Before purchasing major appliances or heating and ventilating equipment, consider some basic questions and facts that may affect your decisions. Buy from a reputable manufacturer or dealer, understand any warranties supplied, and find out about service, installation, and part availability. If possible compare each units efficiency and energy usage to insure the best overall performance. Be sure electrical, gas, and other hook-ups in your home will be adequate to handle the appliance load.
  
  
  
  
• Read and make sure you understand installation, operating, and maintenance instructions. Establish whether the dealer will be installing and testing the device. Confirm a delivery date with the supplier and be on hand to supervise installation and testing. Remember to fill out any warranty forms, and to read, understand, and safely store all operating manuals.
  
  

Energy Efficient Housing Construction: Heating

Heating Systems

An energy efficient home by definition has very little heat loss because of high insulation levels and airtight construction. This leads to two problems: finding a properly-sized heat source and providing adequate ventilation to maintain indoor air quality.

Except for extremely cold periods, a properly designed and constructed energy efficient home can sometimes gain almost enough daily heat from 'waste' sources such as the heat given off by lights, people and appliances. During sunny, cold days solar energy gains also contribute to reducing the heating load. These heat sources are often called 'internal gains'.

Modern control systems such as programmable thermostats can further help to reduce heating energy consumption.

Sizing the Heating System

Heating equipment in a home must be capable of maintaining an interior temperature of 68 to 72° F (20 to 22°) during the heating season. Heating equipment is generally oversized for most homes, but is even worse if the home is an energy efficient home. This leads to frequent on/off operation reducing both efficiency of fuel use and service life of heating equipment.

A heat loss calculation is required to determine the heating system required. It should have a capacity of no more than 10% in excess of the calculated requirement. Installing the smallest capacity heating equipment to meet the loads will save both energy and money. Calculation of total home heat loss is generally done by heating contractors. Contractors inexperienced in understanding low energy house design and heat loss, however, may still result in drastic over sizing. A simple heat loss calculation method is provided in this section.

Isolating The Heating System

If a fuel burning furnace, boiler and/or hot water heater is required, building an airtight enclosure (mechanical room) around the appliances can help control chimney heat loss. Separate combustion and fresh air supplies feed into this room. No previously heated air is used by the fuel burning appliances and cold outside air is prevented from entering other areas of the home. This isolated room must be insulated and sealed from the rest of the home. Water pipes and heat supply ducts should also be insulated.

Calculating Heat Loss

Calculating the heat loss from a home is quite simple. The heating requirement will be highest when the outside temperature is lowest and there is no solar gain. A cold winter night is when the heating load will be greatest. Heat flows out through all the building surfaces including walls, ceilings, floors, windows and doors.

Heat loss through each surface can be calculated using the following equation:

Heat is also lost through infiltration and exfiltration - air leakage. This heat loss can be calculated using:

Note: change the constant 0.36 to 0.018 Imperial units.

There are also a number of sources of heat gain in a typical house. Not only do the occupants give off heat, appliances and lights contribute significantly to home heating. Each person can provide about 75 watts of heating energy while 200 or 300 watts are available from appliances (like freezers, ranges, refrigerators, etc). The average home therefore provides 500 or more watts daily of the total energy required for space heating.

An example heat loss calculation is shown using Plan 13 from Energy Efficient House Plans post. Plan 13 is a 1,920 square foot (178 sq. metres) two level, rectangular bungalow. If this house was to be built in the Red Deer (Alberta, Canada) area, the outside heating design day temperature is - 26° F (-33° C). A common inside temperature is 68° F (20° C) - the difference between them is 94° F (53° C). Design day temperatures and heating degree days information for your locale is usually available from your local weather office. A short list is provided as an example of January design temperatures and degree days for various Canadian cities.

The first set of equations is used to calculate the heat loss from each of the seven surfaces (substitute the areas, R-values and the temperature difference for each surface from your plan). The air leakage heat loss is next calculated using the second equation. The building air volume is 16,775 cubic feet (475 cubic metres) and an air change rate of one-third (1/3 of the house air is replaced every hour with fresh air) can be used in the equation (a typical rate for a well-built, energy efficient home). Substitute the house volume from your plan into the equation. Using the same temperature difference, the total air leakage heat loss is calculated and added to the surface heat loss figures. Subtracting the heat gain average of 500 W results in a total space heat requirement of 8200 W for this example (8.2 kW or about 28,000 btu/hr).

There are a wide variety of computer software programs available which can be used to more accurately calculate building heat loss. These programs require a detailed breakdown of each building component and complete area weather data. Most of the programs available require a considerable learning curve and are often not practical unless you do a lot of heat loss calculations, are a house designer or are designing a complex solar building.

The efficiency of the heat source must be taken into account when selecting it. In the example, an 8.2 kW heat source would be needed (28,000 btu/hr). If one chooses a 100% efficient electric heating source, the exact figure calculated above can be used to size equipment. Gas furnaces range from 70% to 80% efficient (measured seasonally - over an entire year of operation). Divide the heat load (8.2kW) by the system efficiency (0.70) to obtain the 'bonnet' size of 11.7kW (40,000 btu/hr) necessary to provide 8.2kW. Gas-fired furnace and boiler units with efficiencies of 90% to 95% are also available but are usually produced in large output sizes and are more expensive.

Heating Systems - Forced Air

Forced Air Distribution Systems

Homes incorporating forced-air heating systems are very efficient at distributing heat around a home, preventing stagnation of air and moving heat from different sources to the overall space. They also work well with mechanical ventilation systems. The central heat source could be a fuel-fired furnace. Unfortunately the smallest sizes usually available are in the 50 to 60,000 Btu/hr range (18 kW ) and this heating capacity is often much too large for an energy-efficient home. Using such a large heat source is inefficient in terms of fuel consumption. For example, a 50% oversized furnace will use 20% more fuel in heating the same space than a correctly sized unit.

Good heat distribution, air movement, filtering capability, humidity control and low maintenance are some of the advantages with a properly designed and installed forced-air heating system.

A forced-air distribution system works well if a home receives abundant solar energy. Since passively heated spaces can easily overheat when the window area is too large or if there is not enough mass to absorb and store the solar energy, having continuously circulating air with the forced-air distribution fan running at a slow speed helps prevent overheating. Passively heated air is distributed to all the spaces in the home, not just those on the south side.

High Efficiency Gas Furnace

High efficiency (condensing) forced-air gas furnaces offer efficiencies of 90% or better. These units use electronic ignition, induced draft fans and condensing heat exchangers. Ductwork and installation is similar to a standard furnace with the exception of the chimney and condensate drain. Condensing furnaces require a drain pipe connected to a floor drain to allow condensation (water) from the heat exchanger to drain. A standard chimney is not required because the exhaust air temperature is reduced to the point that high temp plastic pipe can be used as an exhaust vent out of a side wall.

The diagram shows a fresh air duct from outside, ducted directly into the cold air return. Combustion air is separately ducted from the exterior to the front of the furnace. Note that both air ducts are insulated. Although not shown, an air to air heat exchanger should be installed to maintain indoor air quality.

Radiator (Fan Coil Unit)

A good heating solution for an energy-efficient house is to use the advantages of a forced air system (such as good air and heat distribution, filtering capability, low maintenance) and add a small auxiliary heat source to it. This could be an electric heating element, a hot water heated coil unit, a heat pump or simply a separate wood or electric unit providing heat that the system picks up and distributes via the forced air system.

This example shows how hot water heating can be combined with a forced air system. Hot water from a boiler is circulated through a radiator placed in the ducting of a forced air system. A fan forces the air through the radiator where the heat is picked up and distributed to the entire house. The duct work design is the same as any forced air system.

An air to air heat exchanger helps to maintain indoor air quality by suppling pre-heated fresh air to the cold air return, which is then distributed to the rest of the house by the forced air system.

Heating Systems - Hydonic Systems

Hydronic Heating Systems

Hot water (hydronic) heating systems usually consists of a boiler and a heat distribution system. This distribution system shows baseboard radiators. A wide variety of radiator types are available. Hot water is supplied directly to the radiators and returns to the boiler by way of a separate line. An expansion tank provides a cushion of air for heated water to expand into if pressure builds up in the system. An insulated fresh air duct provides combustion air directly to the boiler.

Because hydronic systems have no air movement an air to air heat exchanger is used to maintain indoor air quality and transfer heat from the exhaust air to the incoming fresh air supply. Fresh air is supplied (individual ducts) to each room while exhaust air is removed from the kitchen, bathrooms, hallways and laundry rooms. Two separate ducts (intake and exhaust) are installed through the floor header area and must be at least 12 feet (4 m) apart to prevent cross-contamination.

Radiant Floor Heating Systems

Radiant floor hot water heating systems work well in an energy efficient home. Hot water is distributed through water pipes installed in the floor. The layout and distribution of pipes is determined by the building heating requirements. Insulation is necessary under basement floors to help reduce heat loss to the surrounding earth. A reflective material and Insulation are recommended for all floors to maintain heat transfer in the desired direction (usually upward).

With this type of heating system, a balanced mechanical ventilation system which exhausts stale air and supplies fresh air separately (preferably to every room) is essential to maintain indoor air quality. Air to air heat exchangers (also called 'Heat Recovery Ventilators') are recommended for energy efficient homes.

Heating Systems - Other Systems

Electric Systems

Since chimneys are a source of air leakage, electrical heating systems have merit in that no chimney is required. Although electricity is a higher priced fuel, its increased efficiency and minimal capital cost combined with the small required output in an energy efficient home make it a potential alternative.

This system uses an electric heating element placed in a forced air system This combines the benefits of forced air and a small heating system to match the heating load of an energy efficient house. There are also a number of radiant electric (ceiling or floor) panel systems available for home heating.

Fresh air from the heat exchanger is distributed throughout the house by the forced air system.

Heat Pumps

Heat pumps transfer heat by circulating a refrigerant (gas) through an evaporation- condensation cycle, similar to a refrigerator. Winter heating and summer cooling are both handled by a single system. Heat pumps can operate using water, ground or air as the heat source. These systems use electricity to extract heat and under normal operating conditions will produce at least three times more heat energy (or cooling) than they use in electrical energy.

This diagram shows an air to air heat pump system with forced air delivery. During the winter cycle, heat is extracted from the outside air and released into the house. In summer, heat is extracted from air inside the house and dumped outside, thereby cooling the house. One potential problem with air base heat pump systems is that they use more energy than they produce if outside air temperatures drop below 50° (10°).

Combined Systems

Combined systems are now being offered which provide both space heating and domestic hot water. Systems are available which use fossil fuels, heat pumps or electric resistance heating sources to provide domestic hot water and space heating from one unit. Available with smaller output ranges these units should work well with an energy efficient home.

Energy Efficient Housing Construction: Roof and and Ceilings

Roof Construction

Most homes built in cold climates have a sloped roof surface while the interior ceiling can reflect the roof slope, follow a different slope, or can be flat. Because heated air does tend to rise, the recommended insulation levels for ceilings is usually higher than for walls. A complete, well-sealed air/vapour barrier is essential at the ceiling level, but because of light fixtures, plumbing vents and chimneys, can be difficult to install. The air/vapour barrier must be sealed around the potential 'holes' in a ceiling, regardless of the type of roof or ceiling construction. The obvious first step in design is to eliminate as many of these potential problems as possible before they occur in construction.

Air Sealing

The electrical wiring, the various junction boxes, and ceiling outlets create numerous opportunities for breaks in an otherwise continuous ceiling air/vapour barrier. Much can be done to eliminate some of these potential breaks. Using interior wall-mounted fixtures are examples of alternatives. If wiring and outlets are required in the ceiling, using special polyethylene air/vapour boxes or isolating the air/vapour barrier are methods which can be used to maintain the continuity of the air/vapour barrier.

Ceiling mounted exhaust fan installations also cause problems. Firstly, because of the difficulty in sealing around them and secondly because the built-in dampers do not seal well and let warm air leak out. They usually vent through the attic so leaking warm air can cause condensation problems.

If possible, exhaust fans should only be installed on interior walls with ducts routed down the wall and out the floor joist space. This prevents cold air from infiltrating in through the duct pipes.

Plumbing stacks and chimneys are necessary 'punctures' in the ceiling of a home. The ceiling air/vapour barrier can be well sealed to plumbing stacks and vents but the pipes must be securely fastened so that expansion and contraction does not break the seal. An expansion joint, placed in the warm interior, can accommodate pipe movement so that it does not affect the ceiling joint.

Sealing Plumbing Stacks and Chimneys

Metal firestops, properly insulated and sealed are needed to control air leakage around chimneys. Again, by making the proper design decisions, the number of stacks, vents and chimneys may be reduced.

Many homes have an exterior door in their ceiling - an attic access hatch. It is best if the hatch is eliminated from the interior and placed on an outside gable end or through an unheated garage if possible. If not, make sure that the attic hatch door is well insulated, weatherstripped and secured to eliminate air leakage and heat loss.

Roofs and Ceilings

Flat Ceilings

The use of flat ceilings and truss rafters is a common North American building practice. This type of construction leaves an adequate depth in the attic space for loose fill or batt insulation except at the edge over the exterior walls. Modified types of truss rafters can be used to increase the depth at this point.

Maintaining adequate attic ventilation is important. For every 300 ft² of ceiling area, there must be 1 ft² of free ventilation area provided by soffit and roof or gable end vents (a 300:1 ratio - 300 m² of ceiling area vented by 1 m² of vent). This ventilation ensures any water vapour that does find its way above the insulation will be carried out of the space.

Using truss rafters allows the ceiling air/vapour barrier to be installed in one piece. Because the trusses span from exterior wall to exterior wall, the interior partitions can be installed after the ceiling is sealed and covered. However, if partitions must be installed before the ceiling polyethylene is applied, an extra air/vapour barrier strip has to be added to maintain continuity. Any joints must be sealed and must occur over solid backing such as ceiling joists or partition wall top plates. Isolating the air/vapour barrier with strapping is an option which provides protection against tears and provides a space for electrical wiring installation.

Sloped Ceilings

There are three methods of building well-insulated and sealed sloped ceilings. One method is to incorporate a wide joist or flat truss which will leave sufficient space for the insulation and ventilation.

Sloped Truss Ceilings

Another method used for sloped ceilings is to use a scissor truss, which has a flatter bottom slope than top. This type of ceiling is then insulated and sealed in the same method as was discussed for 'Flat Ceilings'. To attain an R-40 value ( RSI-7) a minimum depth of at least 16 inches (400 mm) is required.

Strapped Sloped Joist Ceiling

Strapping the ceiling is the third way of providing a good ceiling insulation level. An isolated air/vapour barrier results. This construction method utilizes 2 x 12 inch (38 x 286 mm) roof joists. At least two thirds of the insulation value must be outside the polyethylene air/vapour barrier.

Energy Efficient Housing Construction: Windows

Window Design

Windows serve a variety of purposes, they are one of the most prominent architectural aspects, can provide ventilation and have a great impact on the energy efficiency and comfort levels of a home. Windows can account for 30 to 40% of the heat loss or heat gain in an energy efficient home.

The overall energy performance of a window unit in a cold climate depends on the glazing (glass or sealed unit), window style or type, frame and sash materials, air leakage, installation and the use of interior coverings or exterior shading devices. Window orientation also plays a large roll in overall window performance due to the combined effects of solar gains, seasonal winds and shading factors. Views, ventilating, natural lighting and passive solar aspects as well as architectural and aesthetic values must be considered. Window types and placement depends on which combination of functions the window must satisfy.

Window selection and placement are key design considerations which effect home energy usage and lighting, as well as comfort and humidity levels. Successful designs usually exhibit a minimal total window area with the majority oriented south for passive solar gain. If possible plan spaces so that most windows face south, while few windows face east or west, and very few, if any at all, face north.

South-facing glass area should not exceed 8 to 12% of the total living area on an energy-efficient home unless new high performance units are used and precautions are taken to avoid potential overheating problems. Opening windows can help control overheating on sunny spring or fall days. If high performance window units are used the total glass area could be increased to 10% or 15% without increasing the overheating potential. Different window sizing rules need to be applied when dealing with increased internal mass, attached sunspaces or mass walls.

Fading, sun rot and damage to finishing materials are problems which can be caused by large areas of south or west facing windows. Low-E window units can reduce the UV portion of sunlight that causes the damage by 60 to 90% while still admitting visible light. One should also select materials such as wood, masonry or special fabrics which will not deteriorate from exposure to direct sunlight. Using a masonry material for floors or walls is an especially good choice since it provides some heat retaining thermal mass as well as being a durable interior finishing material. Framing members may have to be increased in size or number to carry the weight of a masonry floor or wall.

Although living spaces on the south with large windows capture valuable solar energy, there may be times when that heat and glare is undesirable. High performance Low-E units can be used to reduce solar gains and glare from large south or west facing windows.

Vertically designed windows can create a pleasing indoor feeling in terms of natural lighting, viewing and providing ventilation. In bedrooms, furniture placement is often improved with vertical windows. Vertical windows can simply be described as units which are taller than they are wide. On the other hand, it is often difficult to place furniture (like beds or seating units) under vertically designed windows. Because the sills are 32 inches (800 mm) or more above the floor, horizontal windows can be hard for children to open, view out of, or use as an emergency escape.

Adding windows to a side wall or using clerestory windows are two ways illustrated for balancing the natural light. In addition, clerestory windows can bring natural light deep into a building - north side rooms with no other windows, for example. Skylights work well for natural lighting but can cause problems in cold climates. Light pipes or tubes offer a new option for providing day lighting in cold climate homes.

Window Coverings

Interior and exterior window coverings can be used to provide control against overheating and night time heat loss. Louvred horizontal or vertical blinds, shutters or awnings are devices which can be utilized - either on the outside or inside to block the sun. Screening devices used on the outside are more efficient at blocking incoming energy but can be difficult to operate in the winter. Movable window insulation can also be used to help control heat losses. In addition to lowering heat losses, window insulation can function as the window covering (eliminating the need for drapes), control heat gain in the summer, provide privacy and protection and reduce convective drafts near windows. Swinging or rolling shutters, thermal curtains or shades and between-the-glazing insulations are some of the types commercially available.

Window Units

When shopping for window units look for high performance windows which have high tested unit R (RSI) values. Units must offer good durability and materials, while meeting your design and budget requirements. Current window units offer a variety of new technologies and thermal improvements to reduce heat loss and condensation problems.

• Low-emissivity - Low-E coatings applied to interior (or exterior) glazing surfaces which reduce the radiant heat losses and can be used to control solar gains.
  
• Insulating, inert gases (like Argon or Krypton) between the window panes reduce convection heat losses.
  
• New insulating spacers and low-profile insulating frames combined with better air sealing on opening units, have improved solar gain while reducing air leakage and conduction heat losses.
  
• Low-E coated films made of thin polyester or plastic between two panes of glass provide lighter weight, high performance, multiple-glazing units.
  
  

Window Types

Fixed window units are large expanses of glazing primarily for viewing through. The frame and the sash are both fixed in place, do not open and may have multiple glazings. Fixed units are the most energy efficient.

Horizontal Sliders come in several combinations. Choose ones with a fixed window on one side and a sliding window on the other, much like a patio door. The window segments may have double, triple or high performance glazing units incorporated into the design. Units are difficult to weatherstrip effectively, subject to air leakage and are not recommended for energy efficient homes.

Casement windows operate much like a door. They have side mounted hinges, a hand crank which opens the window and pivot on a vertical axis. Some units have a hand crank that swings the window open and then slides the window to the centre of the opening. Two hatch-levers on the sash lock the window to the frame, pulling it tight against the weatherstripping and provide good security. These windows are the easiest to weatherstrip effectively and are consequently the most draft free of opening windows.

Awning windows are very similar to casement windows except they open to the outside from a hinge along the top. They are very weather tight, provide good security and can be compared to a casement in overall energy efficiency.

Tilt and turn windows have special hardware that allows the window to tilt in at the top or to open like a door, toward the inside. These windows are also very weather tight, comparable to awning or casement in energy efficiency with a locking type handle and good security.

Pivoting windows are common in Europe. They pivot in the centre of the frame in a vertical or horizontal axis depending on the model. Moderately airtight, this window type is not a good choice in 'buggy' climates as it is difficult to screen effectively.

Bay or Bow windows are extremely popular. They are windows that jut out on a cantilever floor section, with a series of fixed or opening units joined together in a 3 window or 5 window configuration. Care must be taken to ensure that proper insulation and vapour barrier techniques are applied to the floor area or condensation, drafts and cold floors may occur.

Combination windows are simply an amalgamation of several different units such as fixed units and casement windows. These usually come pre-assembled from the factory ready for installation.

Skylights

Good quality skylights can be an asset to any home during a long indoor winter. In cold climates, choice and placement of skylights has to be done carefully in order to avoid overheating and sun damage during the summer and excessive heat loss with dripping condensation in the winter. Skylights can on the other hand provide a view of cloud scapes and sky, while allowing light deeper into the home than wall mounted windows can, especially on cloudy days.

Glazings for skylights are available in acrylic, polycarbonate, polystyrene and glass. The requirements for a skylight unit should be at least the same as those for a high performance window unit or better.

The deeper the well of the skylight, the less air circulation and the greater the potential for condensation. Flaring the well at the bottom of the shaft will increase air circulation and the amount of light being delivered by the skylight. Sealing a piece of glazing at the ceiling opening of the skylight well can also help. The light well that frames the skylight should be finished in a light colored paint or mirror to allow the well to reflect the maximum amount of light.

When choosing a skylight consider the slope of the roof in relation to the shape of the skylight. Flat skylights on a low slope roof tend to collect snow and dust more readily than dome or pyramidal shaped skylights. Opening skylights can vent hot air out of a house rapidly but may need regular maintenance in order to seal effectively when they are closed. Also, opening skylights should be equipped with a screen.

When placing a skylight on your home, southern or western exposures should use glazing which is tinted, or has a Low-E coating that blocks at least 50% of the solar gain and 90% of the ultra violet light. Consider the percentage of roof area that skylights will cover in any one room. Skylights are usually poor insulators and large areas of roof glazing can be a source of cold drafts and condensation problems on long January days and nights.

Exterior Doors

Energy efficient exterior doors should have an insulated core bonded to the inside and outside skins of steel alloy, aluminum, fibreglass or wood composite. For cold climates insulated doors are a good choice. With much higher insulating values (R-10, RSI 1.8) insulated doors are less prone to warping and are easier to weatherstrip effectively. A door may also have one or two 'side lites' of glass which should be high performance glazing units. Metal doors should have good quality compressible, magnetic or adjustable weatherstripping to reduce air leakage.

Patio Doors

Patio doors can be the largest window in your house. All the components that make a good high performance window also make a good patio door. Triple glazing is very seldom found in a patio door as it is heavy and requires a very thick unit. Some patio doors have two sliding panels while others have one panel fixed and one panel that slides. Sliding doors are very difficult to weatherstrip. Friction and foot traffic wear the weatherstripping out in short order. Rollers can also wear out, requiring replacement. A better type of sliding patio door is available that operates like an airplane door - popping in and sliding away from the weatherstrip with a latching type handle.

Garden, Terrace or French doors are a better choice for energy efficient homes than traditional sliding patio doors. These are similar to double entry doors, with a large glazing area, and one or both opening inwards. Units are available with insulated cores, high performance glazings and can be weatherstripped very effectively. Screens attach to the inside or are mounted on a track on the outside.

When designing a new home take into consideration the location of patio doors. Avoid northern exposures and prevailing winds. Good installation is also critical. Poor installation can cause poorly operating doors, drafts and increased condensation problems.

Energy Efficient Housing Construction: Exterior Walls

Exterior Walls

This section describes types of wall construction and how walls are connected to the floor, ceiling and foundation construction to maintain airtightness and high levels of insulation. The major obstacles to well-insulated and sealed walls are the necessary penetrations in the wall such as doors, windows and electrical outlets. Again eliminating as many potential problems as possible in the design stages is the first step - place wall switches on interior partitions, locate exhaust fans on interior walls, use the most energy efficient windows and doors possible.

Since there does need to be some electrical outlets on exterior walls, they can be installed using polyethylene air/vapour boxes for wall outlets. Some of the wall details show an isolated air/vapour barrier so that electrical wiring can be installed inside the polyethylene layer. Floor or baseboard outlet systems can also be used to eliminate the problem of outlets on exterior walls.

Wall Penetrations

The rough opening space left around installed doors and windows creates a special sealing and insulating problem on exterior walls. Always use good quality window and door units to minimize air leakage heat losses through the unit. They must however also be installed properly to eliminate air leakage around the units. An air/vapour barrier strip can first be sealed (caulked) and attached (stapled) around the outside of the door or window frame. Once the unit is installed the cavity between the rough opening and the window frame is then insulated. This strip is then attached and sealed to the wall air/vapour barrier to create an airtight seal around the opening.

Single Stud Walls

The use of a single stud width for exterior walls is the most common form of North American residential construction. To obtain an R 20 rating (RSI 3.5) in a single stud cavity, 2 x 6 inch (38 x 140 mm) construction must be used. This is an absolute minimum wall R-value level for energy efficient housing. To maintain air/vapour barrier continuity from lower to upper floors, the polyethylene air/vapour barrier can be carried around the floor joists during the early stages of construction. If extra exterior or interior insulation is not being added the walls should be offset 2 inches (38 mm) over the edge of the subfloor so that a piece of rigid insulation can be added to the outside of the joist space (required to keep the air/vapour barrier on the inside of the insulation). Box beam lintels can be made of plywood and are one way to increase the insulation through lintels over windows and doors. Installing rigid insulation between header plates is another method.

Exterior Insulation

In an effort to provide more insulation (as well as blocking the thermal bridges through the wall studs, plates and lintels), an insulated sheathing of rigid fibreglass or rigid foam can be applied to the outside of the wall. This provides a 'blanket' over the wall with more insulation applied over lintels, double studs, corners and the joist space. As well, the sheathing layer can extend down to join the foundation covering. Window and door jamb extensions must be used when wall thicknesses are increased.

Interior Insulation

Interior strapping is another method of increasing wall insulation in single stud construction and reducing the thermal conduction through the wall studs. This method isolates the air/vapour barrier in the wall and provides a convenient cavity so that the polyethylene is not punctured for wiring or plumbing. Strapping is placed horizontally across the wall studs which works well with horizontal wallboard application. The wall air/vapour barrier must be sealed to the ceiling (or second floor), floor and foundation polyethylene layers as shown. At least two-thirds of the insulation must be outside the polyethylene air/vapour barrier.

Staggered Stud Walls

A method of increasing wall insulation levels in a single cavity is to use wider plates. Since wide studs would create more of a thermal bridge, a staggered stud wall can be used instead. A good example would be using 2 x 4 inch studs (38 x 89 mm) on 2 x 8 inch plates ( 38 x 184 mm) to create an R 28 (RSI-5) wall. Even wider plates can be used to obtain higher RSI-values. A staggered stud wall does offer benefits in terms of joist space for insulation, but the air/vapour barrier is on the inside where it can be easily damaged.

Double Wall Technique

This wall construction method was developed both to provide a wide wall cavity for high levels of insulation and so the air/vapour barrier could be isolated inside the assembly in a protected position. Two individual stud walls are constructed. The inside one, usually 2 x 4 inch (38 x 89 mm), is the structural wall and is complete with double plates, window lintels and outside sheathing. The air/vapour barrier is placed under the outside sheathing on the outside of this structural wall.

A second stud wall is placed some distance out from the structural wall - its function to provide support for the exterior finishing material. Insulation is placed in the resultant three cavities. The amount of insulation depends on the width of each cavity but there must be at least two-thirds of the total wall insulation value outside the sheathing (so that the air/vapour barrier is in the correct position).

Plywood spacers at the plates can be used to position the outer wall. If a 4 inch (100mm) cavity is left between two 2 x 4 inch (38 x 89mm) stud walls, then three layers of R-12 (RSI 2.1) insulation can be used to give a total value of R-36 (RSI 6.3). Leaving 6 inches (150mm) between the walls would result in R-44 value (RSI-7.7) being the wall total - with R-32 (RSI 5.6) on the outside of the polyethylene layer.

The double wall construction method will result in a home that is super insulated and sealed The single biggest disadvantage for double wall construction is the associated cost increase in materials and labour.

Wall Systems

A variety of wall systems are now widely available which utilize expanded-polystyrene panels combined with wood, steel or concrete structural members. Most of these wall systems derive their structural strength from integral wood or steel framing members embedded inside the insulation panels. These systems use factory built wall sections ready to be erected on site, and are available in R-20 to R-40 (RSI 3.5 to 7.0) values. Comparable roof panels are available up to R-40 (RSI 7.0). Foundation wall panels are also available which use preserved wood and sheathing or steel instead of regular wood as the structural members. A number of manufacturers offer concrete (block type) wall systems for both foundation and above grade walls with rigid insulation inserts.

Engineered structural sandwich panels (often called stressed-skin panels) are also available from a number of manufacturers. Panels generally have a pre-finished interior and exterior membrane enclosing a urethane, polystyrene or other foam core. The skins are typically made of oriented strand board (OSB), wafer board or plywood and some are available with interior surfaces pre-drywalled. Standard wall panels are available in R-20 to R-40 ( RSI 3.5 to 7.0) with roof panels up to R-60 (RSI 10.5).