Foam – Unlike the roof, there is no real construction efficiency advantage of using rigid foam between the studs and there are good alternatives. Rigid foam (EPS, XPS, polyiso) might not be the best choice, particularly if you are concerned about petroleum-based products. There are some exciting and unique insulation options – some that are minimally processed and somewhat more natural.
Cotton batt insulation would be a good choice if it was readily available in Canada. It is not toxic and environmental impacts are low. It consists mostly of recycled material http://www.bondedlogic.com
Sheep’s wool would be a very interesting choice for both roof and walls. It is essentially a by product of sheep raising. It is a very good insulator and is minimally processed. It also insulates when wet, unlike other products. The fibre is extremely durable, maintaining its elasticity for a long time. Its main drawback is cost. Check out www.goodshepherdwool.com
Wood wool is a unique insulation product that would be a first choice for our homes when it becomes more readily available. As we explain in the section about roof insulation, wood wool will hopefully become a viable option.
Mineral wool (Roxul) is a good alternative to fibreglass batt insulation and can be used in both wall and roof systems and for soundproofing internal walls.
Solid wood walls – are one of the most natural (least processed) and renewable (through sustainable forest management) wall construction/insulation options. Solid wood homes can also be very energy efficient and healthy to live in.
Stay tuned for a discussion on straw bale and rammed earth walls….
Most insulation types can be used in our roof systems. Our timber rafters (purposefully exposed to the inside of the ceiling) are decked with locally-produced tongue-and-groove wood paneling. This is covered by a vapour barrier.
Although we are biased toward more natural insulation types, we often use rigid foam. Its rigidity, high r-value and large piece size make the overall roof construction quite simple. Less lumber and other materials are needed. It is possible to achieve a very efficient roof that is not overly thick. Its performance does not change much if it becomes damp. Its rigid nature allows it to work very well with metal roofing as it can actually support the roofing, thereby minimizing other materials and labour otherwise needed to support and connect to the roofing.
We would recommend polyisocyanurate as the foam type. Although recycled content is lower than Expanded polystyrene (EPS), its manufacturing process is more benign. EPS now has no HCFCs but uses Benzene, a carcinogen, in its manufacture. Extruded polystyrene (XPS) is not being considered at all, since it still produces HCFCs and, like EPS, uses Benzene.
The overall cost of using rigid foam on this roof type is competitive; insulation value relative to cost is high.
Properly installed, foam products are durable. Manufacturers like to refer to the long term r-value to make their point.
From a toxicity and environmental standpoint, mineral wool might be even better than foam. However, construction costs would likely be higher (to achieve the same R-value).
Cellulose could be used, but would recommend a tight packed system. Loose filled methods have been known to lead to settling, thereby decreasing in durability and performance over time. It is one of the most environmentally friendly insulations and when tight packed, might not require an additional vapour barrier.
Wood wool is a unique insulation product that would likely be a first choice in both wall and roof applications. Unfortunately it is not yet available in North America. Shipping costs and acceptance by Canadian building authorities need to be examined. The most prominent company is Pavatex, (www.pavatex.com) located in Switzerland. Waste wood is broken down into a fibrous form and then compressed and bonded together by its own resins. It comes in panel form, like rigid foam.
Insulated Concrete Forms
Some strong arguments can be made for choosing to build foundations out of Insulated concrete Forms (ICFs.) In many cases, ICFs consist of foam blocks, which stack and lock together.
ICFs offer the best insulation value of all the foundation insulation types and can lend themselves to easier interior and exterior than Cast In Place systems. ICF’s require less concrete than other methods, which is a direct environmental benefit considering the embodied energy of concrete and environmental impacts of the concrete industry.
ICFs are less physically demanding on the installers than the traditional Cast in Place (CIP) method and installation can be taught in a relatively short time.
Recent literature suggests that the toxicity of expanded polystyrene (EPS) ICFs is low. EPS is the same material used to make foam coffee cups.
Other foundation systems
We will be adding a discussion of rammed earth, beetle-crete and hempcrete for use in foundation and wall construction.
Economic Assessment of Residential Basement System Insulation Options.
Research Highlight. Canada Mortgage and Housing Corporation. January 2007 Technical Series. (search CMHCs website.)
Research project discussing the significance of thermal mass and energy efficiency of log or solid wood homes. This is particularly applicable to our homes built with solid square timber infill, square log dovetail, and solid laminate wood walls.