Industry Suggested “Best Practices” for Energy-Efficient Exterior Wall Coverings
Foam Plastic Insulating Sheathing (FPIS) can improve the energy efficiency of buildings with its remarkable thermal performance on the outside of a building. This insulation, which comes in a variety of thicknesses to accommodate different thermal resistance needs, helps us meet energy code requirements, which can make it easier to achieve LEED or other green building standards.
FPIS is generally used as continuous external insulation attached as sheathing to wood or steel framing. It comes in board or panel form consisting of foam plastic material complying with ASTM C578 or ASTM C1289, including facers as applicable. The Applied Building Technology Group (ABTG) has developed commercial and residential “best practice” guidelines to assist with a variety of application issues when using continuous insulation. The goal is to help architects, manufacturers and building owners understand “sound approaches” for reliable installation. We recommend you take a look.
This helpful group’s guide on “Attachment of Exterior Wall Coverings Through FPIS” breaks the installation process down into a handful of steps – each to optimize the install.
The first step cautions builders about the minimum compressive strength and wind pressure resistance that FPIS must achieve for this sheathing to properly support the exterior cladding. The exterior continuous insulation must have a minimum compressive strength of 15 PSI and must comply with ANSI/SBCA FS100 regarding wind pressure (somewhat obvious, since this is an exterior insulation). The FPIS can be attached to any softwood lumber with a specific gravity of .42 or higher whereas metal frames must have a thickness of 33 mil, 43 mil, or 54 mil to secure the insulation.
Above: Compression testing; Below: Building wind pressures illustrated.
Next, verify fastener location, length of fasteners and suggested methods to attach insulation boards. Exterior wall coverings can be attached using fasteners of proper length, in combination with overlaid cladding or under laid furring. The guide provides excellent installation detail on how to configure fasteners.
Ingredients for sheathing showing here (a) Cladding, (b) Fasteners, (c) Furring, (d) FPIS, (e) Framing, (f) Cavity Insulation, (g) Interior wall finish.
Of course, a builder will square the framing prior to installing the insulation boards. Some of the best practices for stud arrangement framing, blocking, and bracing are shown in the graphics to the right.
Don’t over- or under-drive the foam sheathing attachment fasteners. Always leave a 1/32” gap to allow for thermal expansion of vinyl or aluminum siding when it is used as the cladding.
To ensure that the wall meets manufacturer’s requirements, nails and fasteners must be spaced along the edges of the panels and into interior framing members, per manufacturer’s instructions.
After attachment, trim sheathing boards around window and door openings and ensure joints fit tightly. Apply an appropriate water resistant barrier (WRB) and flashing to ensure code compliance. At pipe and other small penetrations, seal gaps with plastic silicone or expanding spray plastic foam sealant. Seal joints and openings with joint tape per manufacturer’s instructions.