Tempo:
The strips can be installed between the two top plates to avoid damage during construction (Figure 13). The air barrier can be lapped under and taped to the strip of polyethylene at the top of the wall. This is sealed to the polyethylene attached to the underside of the roof framing to ensure that the air barrier system is continuous at the junction between the walls and roof. To reduce air leakage through the attic hatch, install a compressible gasket between the opening portion and the frame and latches to keep the hatch closed.
VAPOUR DIFFUSION CONTROL Water vapour can migrate through building envelope assemblies by penetrating through materials by ‘diffusion’. Many activities such as cooking, dishwashing, laundering and bathing release considerable amounts of water vapour into the air and increase its humidity. As water vapour diffuses through assemblies, it can condense on cold surfaces such as the inside face of the exterior sheathing and cause deterioration.
Vapour Barrier In the winter, the air inside the house may contain more water vapour than the outside air. This causes a difference in vapour pressure and creates a driving force that can lead to water vapour diffusing through materials into the building envelope. Many building materials are permeable to the passage of water vapour, but those classified as vapour barriers, such as polyethylene sheet, have very low permeability and are very resistant to diffusion.
Location of the Vapour Barrier To prevent condensation from forming within building envelope assemblies, materials that act as vapour barriers (vapour retarders), including certain types of insulation, must be located within the assembly so that moisture moving from the inside to the outside does not condense and accumulate within the assembly. This means that vapour barriers should be located on the warm side of insulating materials (Figure 14). An exception to this rule is permitted for walls where no more than one third of the total thermal resistance or RSI-value (R-value) is located on the interior side of the vapour barrier.
13 Installation of polyethylene sheet strips in interior wall framing
double top plate polyethylene or polyolefin air barrier tab stud
VAPOUR DIFFUSION CONTROL Water vapour can migrate through building envelope assemblies by penetrating through materials by ‘diffusion’. Many activities such as cooking, dishwashing, laundering and bathing release considerable amounts of water vapour into the air and increase its humidity. As water vapour diffuses through assemblies, it can condense on cold surfaces such as the inside face of the exterior sheathing and cause deterioration.
Vapour Barrier In the winter, the air inside the house may contain more water vapour than the outside air. This causes a difference in vapour pressure and creates a driving force that can lead to water vapour diffusing through materials into the building envelope. Many building materials are permeable to the passage of water vapour, but those classified as vapour barriers, such as polyethylene sheet, have very low permeability and are very resistant to diffusion.
Location of the Vapour Barrier To prevent condensation from forming within building envelope assemblies, materials that act as vapour barriers (vapour retarders), including certain types of insulation, must be located within the assembly so that moisture moving from the inside to the outside does not condense and accumulate within the assembly. This means that vapour barriers should be located on the warm side of insulating materials (Figure 14). An exception to this rule is permitted for walls where no more than one third of the total thermal resistance or RSI-value (R-value) is located on the interior side of the vapour barrier.
13 Installation of polyethylene sheet strips in interior wall framing
double top plate polyethylene or polyolefin air barrier tab stud
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