Once you have considered your budget and your house’s original construction, you can now decide how much insulation to add, depending on your energy-saving objectives. Table 1 provides general guidance for the amount of insulation to add to the roof/attic, walls, foundation and basement floor, as well as for window and door upgrades, to achieve up to 10-per-cent, 25-per-cent and 75-per-cent space heating energy savings. The number of areas that must be included in the retrofit project, and the amount of insulation to be added, increase with each improvement in targeted space heating energy savings.
|Targeted Space Heating Energy Savings||Retrofit Measures to Achieve Targeted Space Heating Savings|
|Improve Airtightness by at Least 30%||Add Insulation to Roof and Attic||Add Insulation to Below-Grade Walls||Add Insulation to Above-Grade Walls||Replace Windows and Doors||Add Insulation to Basement Floor|
|25%||✔||RSI-3.52 (R-20)||RSI-2.64 (R-15)||RSI-2.64 (R-15)|
|>75%||✔*||On top of roof: RSI-7 (R-40)**|
Over existing attic insulation:
|RSI-2.64 (R-15)||RSI-5.28 (R-30)||RSI-1.04 (R-6) or more||R-1.76 (R-10)|
|* Note: Air leakage should be no higher than 1 ACH50 for space heating energy savings greater than 75 per cent.|
** This is considered to be the highest insulation value that can reasonably be added on top of the roof sheathing.
Note that, no matter what level of energy savings you wish to achieve, all retrofit options require reducing air leakage by 30 per cent or more. Houses built between the 1950s and the 1980s have measured airtightness values generally averaging above 6.0 air changes per hour (ACH50). The air change rate is a measure of how many times per hour a volume of air, equal to the volume of air in the house, leaks through the building envelope at an applied air pressure difference of 50 pascals. If, for example, your house has a measured airtightness level of 6 ACH50 (as determined by the blower door test) before you start the renovation, the measured airtightness of the house post-retrofit should be 4.2 ACH50 or lower.
To achieve a 10-per-cent space heating energy savings, you can choose any one of three options:
- Air seal the house and add an additional RSI-3.52 (R-20) insulation to the existing insulation in the attic.
- Air seal the house and add an additional RSI-1.76 (R-10) insulation to the existing insulation in the basement walls.
- Air seal the house and add an additional RSI-1.76 (R-10) insulation to the existing insulation in the above-grade walls.
To achieve space heating energy savings of 25 per cent or better, you could choose to replace all the windows and doors with ENERGY STAR® units and improve the airtightness of your house at the same time. Alternatively, you could reduce air leakage by 30 per cent and add RSI-3.52 (R-20) insulation to roof/attic and RSI-2.64 (R-15) insulation to above- and below-grade walls.
Finally, space heating energy savings of 75 per cent or better require a more comprehensive approach involving all locations in the building envelope and using insulation with significantly higher RSI-values (R-values) at each of these locations. In addition to air sealing the house, you should add insulation to the roof/attic, above- and below-grade walls, and basement floor.
Note that the insulation retrofits and targeted energy savings are illustrative examples only, intended to show the scope of improvements that may be necessary to attain energy savings in the ranges indicated for a typical house built between the 1950s and the 1980s. The choice of insulation needed to achieve any given level of energy savings will depend on your location and the characteristics of your house. Other combinations of insulation levels and locations may also be possible. Explore the options with your Eco Insulation advisor.
This information is part of the CMHC About Your House — General Series