4.1004.5 Knee Walls and Gable End Walls—Preparation for and Installation of Spray Polyurethane Foam (SPF)

Topic: 
Attics
Subtopic: 
Knee Walls
Desired Outcome: 
Airtight and insulated knee and gable end walls
For supporting material, see General Information on Spray Polyurethane Foam (SPF), Referenced Standards and Building America Solution Center.
TitleSpecification(s)Objective(s)
4.1004.5a
Installation of backing

Knee walls will have a top and bottom plate or blockers installed using a rigid material Rigid material Drywall, oriented strand board, duct board, cardboard, or any other stiff product that may support the load of insulation while serving as a durable air barrier

A suitable backstop material attached to the back of the knee wall Knee wall Any wall between the conditioned space and the attic will be used to support the application of SPF SPF Spray polyurethane foam

If foam sheathing is used as a backstop, sheathing will be listed for uncovered use in an attic or covered with an ignition barrier Ignition barrier Any layer of material that protects another from catching fire due to heat or spark , thermal barrier, or approved alternate assembly

Provide a backstop or substrate for application of SPF SPF Spray polyurethane foam

4.1004.5b
Installation

Insulation will be installed to prescribed R-value

Using SPF SPF Spray polyurethane foam application, SPF SPF Spray polyurethane foam will be applied to desired thickness onto substrate material from top to bottom plate between studs using pass thickness maximum in accordance with manufacturer specifications

In colder climates ( IECC IECC International Energy Conservation Code Zones 5-8), the SPF SPF Spray polyurethane foam will be installed to a thickness of at least Class II vapor retarder Vapor retarder A material that slows the passage of water vapor and contains a perm rating above 1 or have at least Class II vapor retarder Vapor retarder A material that slows the passage of water vapor and contains a perm rating above 1 coating or covering in direct contact with the interior of the SPF SPF Spray polyurethane foam

Eliminate cracks, gaps, and voids

Minimize framing cavity air flows

Minimize moisture migration and unwanted condensation in insulation (vapor retarders)

Ensure alignment of insulation and air barrier Air barrier The separation between the interior and exterior environments of a building that slows air flow to the point that no smoke movement is visible at 50 pascals of pressure difference across the boundary

4.1004.5c
Onsite documentation 		A dated receipt signed by the installer will be provided that includes:
  • Coverage area
  • Thickness
  • R-value

Document job completion to contract specifications

Confirm amount of insulation installed

Comply with 16 CFR 460.17