Current building codes are requiring enhanced levels of thermal performance when renovation permits are applied for. This can have large cost impacts on the renovation project but this can also create great improvements in the performance of your house.
The components of a wall or roof that provide thermal performance include:
- the vapour retarder
- interior moisture (vapour) is created simply by our living: breathing/sweating, cooking, cleaning, drying wet clothes, etc.
- from simple physics moisture moves from warm to cold so during cooler times of the year interior moisture/vapour is trying to push through the exterior walls or roofs from the warm interior condition to the cold exterior
- if too much moisture can get through the exterior walls or roofs there is a danger that it will condensate when it arrives at a cold enough surface such as the framing components on the exterior of the wall thus creating bulk moisture in the wood framing and insulation of the exterior wall e
- this may lead to mould, structural damage, and deterioration of the performance of the insulation
- the vapour retarder slows the passage of the water vapour, which diffuses through the wall surface, into to exterior wall assembly
- the vapour retarder should keep the level of vapour low enough that it can naturally dry out of the wall cavity without building up to damaging bulk water
- the vapour retarder MUST be on the “warm” side of the insulation to be effective
- the vapour retarder could be traditional polyethylene film or it could be a primer/paint or wall finish that retards vapour passage
- the air barrier
- if interior air can escape to the exterior warmth that has cost to heat is lost to heating the exterior environment
- also, air that can freely travel through a wall either in or out can carry moisture with it causing damage within the wall assembly
- to have a wall that performs well thermally an air barrier must be effective
- mechanical heating and cooling systems rely on a properly functioning air barrier
- the air barrier must be strong and durable and remain intact sealing all areas of the wall and penetrations through the wall
- the air barrier can be anywhere within the exterior wall assembly provided it is continuous and supported
- the air barrier and the vapour barrier can be the same material (i.e. polyethylene film) if installed on the warm side of the insulation or the air barrier can be elsewhere in the wall (i.e. airtight foam insulation) or on the exterior of the wall sheathing (i.e. housewrap) placed behind the rainscreen and cladding
- the thermal insulation
- the thermal insulation has traditionally been placed within the stud framing of the exterior wall or the rafters or roof joists in a roof assembly
- with 2×4 framing this generally meant R12 (traditional fiberglass) or R14 (rockwool) insulation and with 2×6 framing this meant R20 or R22
- Saying a wall had R12 or R20 insulation with insulation between the framing materials was not correct though as every framing member (stud, joist, rim joist, rafter) reduced the overall effectiveness of the insulation inbetween
- If you have an older house with 2×4 stud wall framing you would, under a renovation, have to upgrade this insulation to achieve R15.6 average overall (accounting for studs) in BC Building Code covered municipalities and R22 in Vancouver Building Bylaw for Vancouver.
- To achieve this you have two choices which include making your existing framing thicker by adding strapping to your existing walls or installing insulation on the exterior of your building.
- To add strapping to your existing walls you will lose some interior floorspace and have to redo all your interior drywall and trims or to add insulation to the exterior of your walls you will have to remove all your exterior cladding and restore it over a continuous layer of rigid exterior insulation
Thermal upgrading will provide a much more comfortable house and, done correctly, should eliminate drafts and greatly reduce energy use for both heating and cooling. The house will also likely be quieter. Concurrent with the exterior wall upgrading would be new windows and doors that would also thermally perform at a much higher level.