Summary

• This is a very durable wall overall in all the climate zones listed, due mainly to the rain screen properties of the vinyl siding. The vinyl siding is non-absorptive to moisture, thus avoiding solar-driven moisture issues, while maintaining excellent drying potential towards the outside due to the "air-leakiness" of the siding (should any moisture find its way into the wall). The rest of the wall assembly is also relatively vapour permeable outboard of the polyethylene vapour retarder, maintaining excellent drying characteristics towards the outside.

Energy & Thermal Performance

• This wall is subject to some thermal bridging due to exposure of framing elements to outside temperature conditions.
• The framing factor for this wall at 24" o.c. is 20% (i.e. 20% of the wall is wood only and 80% is insulated)
• Advanced framing as defined by NBC 9.36.2.4. (1) (e.g. insulated headers, 2 stud corners, ladder blocking, and in-line framing) can potentially reduce the framing factor by 10% to 20%)
• Maximum nominal R-value of cavity insulation is typically limited to R19,20,22,24 (fiberglass batt) to R30 with medium density spray-applied insulation

Exterior Moisture/Wetting

• Any liquid water leaking past the vinyl siding will be intercepted by the asphalt impregnated 30 minute paper with lapped joints, lapped over a flashing at the bottom of the wall assembly which acts as a secondary drainage plane and will be drained to the outside
• The vinyl siding is non-absorptive and rain shedding
• Any moisture which may leak into the wall through penetrations can dry to the outside due to the "air-leakiness" of the vinyl siding, and the excellent drying characteristics of the whole assembly
• Care must be taken at penetrations (windows etc.) by use of proper detailing and use of flashings/ sealants etc. so that water does not leak into the assembly

Air Leakage Transported Moisture from Inside

• Air leakage into the wall must be managed by means of a continuous interior or exterior air barrier (preferably both), combined with proper detailing at any connection or penetrations (window openings, electrical boxes, plumbing penetrations etc.), which will also help reduce heating and air conditioning costs
• This wall assembly has excellent drying potential towards the outside due to the "air-leakiness" or "breathability" of the vinyl siding

Water Vapour Diffusion from Outside

• Solar driven moisture is not an issue with vinyl siding and other similar non-absorptive and rain-shedding sidings

Water Vapour Diffusion from Inside

• Should moisture get into the assembly, it has very good drying potential towards the outside:
  o Fibreglass batt is very vapour permeable
  o Wood sheathing is relatively vapour permeable when on the cold side of a wall, where relative humidity is typically higher
  o Asphalt impregnated 30 minute paper is vapour permeable
  o vinyl siding is "air-leaky" or "breathable", allowing convective drying to the outside
  

Ease of Construction

• This wall is easily constructed through traditional stick frame methods on-site
• Exterior wood sheathing provides both structural resistance to "racking" and a nailing substrate for cladding materials
• Insulation, weather barrier and air barrier details and materials are readily available and understood within the Canadian industry
• Materials such as studs, wood sheathing panels and/or insulation sheet goods are readily available in pre-cut lengths for 8' and 9' wall heights
• Advanced framing as defined by NBC 9.36.2.4. (1) (e.g. insulated headers, 2 stud corners, ladder blocking, and in-line framing can potentially reduce the framing factor by 10% to 20%) could be further enhanced through in-line framing wherein double top plates can be limited to single plates (this is most efficiently done by referencing the roof truss layout spacing prior to laying out the first wall assembly) . See http://www.performancewalls.org/?content=app_pf_afadvantages.

Affordability: Cost Implications

• Alternative bracing methods can be substituted for the wood sheathing panel (e.g. T-slot inlet bracing) - however, details for wall bracing, tall walls, and more than 3-storey construction may require additional engineering
• Advanced framing as defined by NBC 9.36.2.4. (1) (e.g. insulated headers, 2 stud corners, ladder blocking, and in-line framing) can potentially reduce overall lumber costs by upwards of 10 to 20% (i.e. for softwood and panel products)

Esthetics: Architectural Design

• Exterior wood sheathing provides a nailing substrate for cladding materials including various siding applications (vertical or horizontal)

Additional Sources of Information

• Designing Energy Efficient Building Enclosures, FPInnovations
  
  
  High R Value Enclosure Assemblies, Building Science Corporation
  
  
  Guide to Attaching Exterior Wall Coverings through Foam Sheathing to Wood or Steel Wall Framing, FSC