By Mark Boudreau
Let’s start with the basics, insulation. It resists the flow of heat from one location to another. A good insulator is a material that is really good at keeping heat from transferring from one location to the next.
Take a thermos bottle. You put your hot coffee in the thermos, go out for a ski and in about an hour you stop. Your thermos has been exposed to the 5º temperatures but when you pour your first cup it is still as hot as when you made it. It is a simple concept. The walls of your thermos have resisted the heat transfer that takes place because heat seeks to move from a region of high heat to a region of low heat. The insulation in your thermos keeps the heat in better than, say, a ceramic cup which transfers heat from the hot liquid to the outside surface of the cup to warm up your hands. That heat is leaving the liquid at a much faster rate than the thermos. Resistance is the key word here — the “R”-value. Different materials resist heat transfer at different rates of time. The ceramic cup’s R-value is lower than that of the thermos.
In houses we discuss R-values a lot. In fact there are certain benchmark R-values that we actually try to achieve in different parts of the house. The average house that our design-build company audits usually has wall R-values of between 10 and 30. Attics’ R-values range between10 and 70. Basement R-values range between 5 and 30.
For your house to stay warm you need to add heat to it. Your heater output is measured as BTU’s (British Thermal Units). Over time that heat leaves the house to the outdoors, and generally leaves no matter what you do. You can change how quickly it leaves though. The rate that the heat transfers through the walls, ceilings and basement is determined by the R-values of those areas and their insulation. For houses with low R-values, the heat transfer (loss) happens faster so your heater has to keep adding heat to keep you warm. This is costly to your wallet and to the environment. Having high R-values means the heat that is put into the house stays there a lot longer, requiring less heat to keep your space warm for longer time.
There is a fairly wide variety of insulations on the market. There is no best insulation. Each insulation has its pros and cons. Here are the most common ones and their R-values.
|Insulation System||R-value per inch||Pros||Cons||Best Use|
|Cellulose: Shredded newspaper||R-3.7/in. (loose blown)
R-3.2/in. (dense pack)
|Recycled paper, green product, dries well and resists mold and rot. Inexpensive. When the house’s life-cycle is over it will decompose easily.||Cannot be used in all situations. Requires a lot of area/volume to get higher R values. Requires a very good airseal.||Wall cavities, attics, roof cavities|
|Spray foam insulation. Polyurethane based foam product that is sprayed as a liquid and quickly cures as a solid foam. Also comes in preformed rigid foam boards of many varieties which can be used in insulation of walls, basements and attics.||R-5/inch
|Outstanding airsealer and insulator. Excellent ability to get into hard to reach areas and applies well to uneven surfaces||Requires specialized equipment and installers. Is expensive. Is not environ-mentally friendly. Will not decompose easily after the house’s lifecycle is complete. A product of its burning is cyanide gas.||Stone wall basements, difficult to reach places in a home where airsealing and insulation would be very difficult or costly.|
|Mineral wool insulations. Molten mineral spun into bers.||R-3/inch||Very good insulator. Greener product than berglass insulation. Inexpensive||Great care must be used in installation as any voids or compression will DRASTICALLY reduce r-values||Walls and attics|
|Fiberglass Insulation. Molten glass spun into bers.||R-3/inch||Very good insulator. Not particularly environmentally friendly. Inexpensive.||Great care must be used in installation as any voids or compression will DRASTICALLY reduce r-values||Walls and attics|
Remember that insulation is only as good as the air-sealing that is done in the house. A VERY COMMON MISTAKE is for people to add insulation in their attic but not do any air-sealing. You can have 20 inches of fiberglass insulation which you would expect to give you R-60, but if the insulation is installed poorly or if you have not air-sealed the attic well you may end up with an “effective” or actual R-value of around R-14 for that 20 inches of fiberglass. Air-sealing and Insulation should always happen together. Like the winning combination of a warm sweater and a great windbreaker your insulation will keep that heat in your house, keep you comfortable and keep your heat system from working as hard as it otherwise would.
Consult with an energy consultant or home performance professional to help you decide which insulation is the best for you, your values and what you are trying to achieve.
Mark Boudreau is co-owner of Lewis Creek Company, a full-service design-build company consisting of both trades-women and men located in North Ferrisburgh, VT. Their holistic approach to new building and renovating considers people, homes, the environment, beauty, economy, and performance.