Insulation and Heat Loss
Insulation slows the rate at which heat is lost to the outdoors. Heat flows in three ways: by conduction, convection and radiation. The main function of insulation is to keep the heat in. To be effective, insulation must be:- resistant to heat flow
- able to fill a space completely and evenly without compacting
- durable
Several different insulation materials may be used at various locations as part of the house envelope, depending on available space, ease of access and other installation requirements. In short, the choice of insulation will largely depend on where and how it will be used.
Still air is not a good conductor of heat and can be a relatively good insulator. However, in large spaces such as wall cavities, heat can still be lost across the air space by convection and radiation. Insulation divides the air space into many small pockets of still air; inhibiting heat transfer by convection. At the same time, the insulation material reduces radiation across the space.
Insulation is manufactured and sold in units defined by its thermal resistance value, called the R value – a precise measurement of resistance to heat flow. The higher the R, the slower the rates of heat transfer through the insulating material. One brand of insulation may be thicker than another, but if they both have the same R value, they will resist heat flow equally well.
Proper installation is a must for insulation to work effectively. There are specific instructions for installing insulation in attics, basements and walls. Some common guidelines; however, apply wherever insulation is installed.
Your choice of how much insulation to add will depend on many factors such as local housing codes, amount of insulation already in the house or house construction. Table 1 indicates suggested thermal resistance R values for Alberta’s climate. The metric equivalent of the R value is RSI value, some insulation products may have RSI indicated on the packaging as well.
Table 1
|
Area |
Thermal Resistance Value | |
|
Roof (attic) |
R |
38 |
|
RSI |
6.7 | |
|
Walls |
R |
23 |
|
RSI |
4.1 | |
|
Basement Walls |
R |
17 |
|
RSI |
3.0 | |
|
Floors (over unheated areas) |
R |
38 |
|
RSI |
6.7 | |
Naturally, cost is a factor in the choice of material. Generally, the cost-per-R value is lower for loose-fill or batt materials than it is for rigid board or foam insulations. However, the price of the basic material is just one aspect. In some cases, high material costs may be offset by lower installation costs.
The vapour barrier is an important component of a re-insulating job as it provides some protection from moisture damage to the structure and the insulation materials. It must be installed on the warm side of insulation. To be effective, the vapour barrier must be impervious to the flow of water vapour and durable.
Alberta Government Insulation Rebate
All Albertans who participate in the federal government's ecoENERGY Retrofit Program and perform qualifying insulation upgrades on or after January 1, 2009 are eligible for a provincial rebate. Visit Climate Change Central for more rebate information.
For additional energy saving tips, read Climate Change Central's article Fall into Efficient Home Heating.
