Oct 26 2012
For many Canadians, there are many attractions to buying a newly constructed home. These include new, up-to-date finishes, modern floor plans and amenities, comfort and energy efficiency. When considering your options, energy-efficient heating, appliances and lighting are common choices.
But what about the amount of insulation for the walls? The construction of a new home offers the best opportunity to build in as much insulation as you can afford in order to protect yourself from heating cost increases in the future.
You may have heard of different types of walls being built in energy-efficient houses: walls that retain more heat in winter due to the high levels of insulation that they contain. Some of these walls have over twice the thickness compared to more typical walls and this provides greater protection from extreme cold and heat, traffic noise, and everything else that is happening outside. Other benefits are significant savings on your heating and cooling bills and a very comfortable, draft-free home. Why wouldn't you build like this for your next new house or major retrofit?
Energy-efficient houses
You can achieve a highly insulated, RSI 7 wall (or R-40 in imperial units), if you design and build carefully. This compares very favourably to the standard RSI 3 - 5 walls found in most new houses. Over the past few years, Canada Mortgage and Housing Corporation has been working with leading builders to design, build and demonstrate highly energy-efficient houses that produce as much energy as they consume. All of the houses constructed use highly insulated walls as part of the overall strategy to reduce energy use. For instance, the Riverdale NetZero house in Edmonton has a deep-wall construction with 406mm (16 inches) between the inside surface and the siding on the exterior. That space was filled with cellulose insulation made from recycled newspapers. During construction of that house, before the heating system had been installed, the interior of the house would warm with the sun and be comfortable, even in sub-zero outdoor temperatures. The calculated insulation level of these walls is RSI 9.9 (or R-56). A deep wall also provides an opportunity to include window seating and plant shelves in the window nooks.
The Green Dream Home in Kamloops, BC used another approach. The walls are made from insulated concrete forms (ICF). ICFs are made up of two layers of expanded polystyrene (EPS) held apart by plastic bracing and are assembled much like building blocks to form the foundation and above grade walls of houses. Once up, the ICFs are filled with concrete to provide structural strength. For the Green Dream Home, the foam insulation used was thicker than normal with 66 mm (2 5/8 inches) of EPS on the inside surface and 134mm (5 3/8 inches) on the outside and 200mm (8 inches) of concrete in the core. The total R-value of this wall is RSI 7.7 (R-44). The continuous layer of concrete within the forms also helps to make the house airtight and draft-free.
If you are retrofitting an existing house with high R-value walls
The strategies will be somewhat different, and a little more difficult to do. Your existing walls will remain as the house frame but you will have to decide whether to insulate on the inside of the house or on the outside. As inside work is more disruptive, insulation is often added on the outside. It is most cost effective to consider adding insulation when it is time to replace or update the siding since you would already be doing much of the work. High amounts of insulation can be added to the outside of the frame, usually as overlapping layers of foam board or as spray-applied foam insulation. Semi-rigid mineral wool insulation can also be used. It is rare for a retrofit to attain R-values as high as those of the new houses described above, but you can still double or triple the original insulation value with the installation of 50 to 100mm (2 to 4 inches) of insulation on the outside of your home.
Consult an expert
Whether you are dealing with a new wall or an existing wall, it is best to consult a qualified designer, builder or renovator who is knowledgeable about the type of work you want done. A well planned project can help ensure that you use resources properly and in an environmentally conscious way. For instance, you may be able to use recycled building products. Well-designed walls will avoid moisture problems and provide many years of trouble-free service. They will also be affordable to build.
Why do it?
The beauty of building or retrofitting very efficient walls in your house is peace of mind. They make your house quiet, comfortable, and relatively immune to the increasing cost of energy. You will also have the comfort of knowing that you may be able to stay in your house longer in the event of a mid-winter power failure. Consider also that the choices you make today will have an impact on the energy performance and comfort of the house for as long as the house exists, and this could be well over 100 years. Once built, energy-efficient walls will continue to save energy for many, many years to come. Great walls help make a great house.