|Conceptual Reference Database for Building Envelope Research||
wood frame wall requirementSource: (www.wkpower.com/powersense/articles/framing.html)
Framing: Requirements of exterior walls: a) must have strength and rigidity b) must control heat flow c) must control air flow d) must control water vapour flow e) must control liquid water movement f) must have stability and durability of materials g) must be able to contain fire within the space and protect the space from fire outside the building h) should have aesthetic considerations with regards to the appearance of the all i) should take into acco unt the total cost of the wall system
Some problems associated with exterior walls: a) cracking of the exterior cladding (particularly masonry) b) spalling (large sections coming loose) of exterior cladding (particularly stucco) c) efflorescence (staining or discoloration) of the exterior cladding. (brick or block) d) rain penetration to the interior of the building e) problems associated with concealed condensation f) surface condensation on the w arm side of the wall
Air tightness is critical to the longevity of an exterior wall system, so concentrate on installing a completely sealed air-vapour barrier. The common method used to install an air-vapour barrier is the placement of polyethylene film (6 mil) on the warm side of the insulation. This should be completely sealed to prevent any leakage into the wall cavity of moist air. Another method is to use the interior finish (i.e drywall board, plywood, etc.) as an air barrier, then utilize interior paint as the vapour barrier. Gaskets are used to join all building materials.
Some various wall construction methods include:
a) 2 x 4 @ 16" O.C. c/w R12 batt insulation and sheathing b) 2 x 6 @ 24" O.C. c/w R20 batt insulation and board insulation or sheathing c) 2 x 8 plates with 2 x 4 @ 16" O.C. inside and 2 x 4 @ 24" O.C. outside c/w 5/16" sheathing or board insulation d) 2 x 4 @ 16" O.C. with 2 x 2 horizontal strapping @ 24" O.C. c/w R12 batt insulation and 5/16" sheathing c/w R10 foam insulation inside or R8 batt insulation inside (e) double wall - 13" thick 2 x 4 @ 16" O.C. inside 2 x 4 @ 24" O.C. outside with 2 layers of R 12 batt insulation 1 layer of R20 between - 5/16" sheathing outside.
The last option would be the most cost effective per "R" value.
Another method used primarily to ensure a complete seal and continuous vapour barrier is to construct the outside wall with either 2 x 4 or 2 x 6 @ 24" O.C. with R12 or R20 batt insulation. A 6 mil poly vapour barrier is positioned on the warm side of the wall and sealed completely. 2 x 2 @ 24" O.C. strapping is then applied horizontally to the inside of the wall. This cavity is utilized to run the electrical wiring and outlets. Drywall board is then applied as the final step to the inside. Another option to this method for additional insulation is to apply rigid insulation to the exterior of the wall in lieu of sheathing and then finally the exterior finish.
One must ensure insulation is installed tight to the exterior sheathing in the wall cavity so as not to allow an air space between the insulation and exterior sheathing. An air space can encourage convective currents further complicated by electrical boxes and wiring protruding into the wall cavity creating further voids.