A continuous thermal barrier is made up of two components: an air seal that encloses the entire home and a continuous blanket of insulation that reduces the transfer of heat/cold from the outside to the inside. A continuous thermal barrier has a number of significant benefits:
- Keeps the home quieter and warmer in winter and cooler in summer
- Reduces the allergens and pollutants entering the home
- Enables a smaller, less costly HVAC unit that runs for shorter periods of time
The thermal barrier that is continuous or covers the whole house maximizes the effectiveness of the insulation and reduces the impact of “thermal bridging”. A “thermal bridge” is a material, such as a wooden wall stud, that provides a pathway for heat or cold to move more easily from the outside to the inside of the house.
Looking at the attached thermal image photo on the left you can see the wall studs in this home acting as a thermal bridge and allowing cold to enter the house via the wood stud pathway. This is an illustration of a conventionally framed and insulated home where insulation is only placed in the cavities between the studs. If wood makes up 25% of a wall the overall effectiveness of the insulation in the wall cavity is reduced as the cold bypasses the insulation by hopping on the wooden “thermal bridge”.
The thermal image on the right shows the same home with a continuous air seal provided by an additional layer of insulation on the exterior of the home. This additional layer is normally a rigid foam type product that insulates, air seals, reduces the impact of “thermal bridging” and increases the overall effectiveness of the insulation within the wall cavity.
The externally applied rigid foam also acts as a vapor retarder in much the same way as a house wrap acts as a rain shield or drainage plane between the house sheathing and siding. The rigid foam will allow some vapor to pass inside to the internal wall or outside to the rain screen. When using rigid foam as an exterior insulation it is recommended to also use a vapor retarder (not a vapor barrier) between the wall board and the cavity insulation. In other words, use a vapor retarding material on both sides of the wall to prevent condensation buildup inside the wall.