Improving Performance of a SIPs Roof - Fine Homebuilding

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Editor's Notepad

Editor's Notepad


Improving Performance of a SIPs Roof

comments (0) November 14th, 2011 in Blogs
ScottG Scott Gibson, contributing writer

Rot in a SIP roof: Unchecked air leaks in a structural insulated panel roof can lead to decay. That was the conclusion reached by Joseph Lstiburek, a principal at the Building Science Corporation, after investigating roof failures in Alaska. The question is whether a layer of rigid foam on top of the panel has the potential to trap moisture and create a similar problem.
Seal and ventilate: Lstibureks recommendation for avoiding problems is to seal seams between panels carefully and add a means of removing moisture.
Rot in a SIP roof: Unchecked air leaks in a structural insulated panel roof can lead to decay. That was the conclusion reached by Joseph Lstiburek, a principal at the Building Science Corporation, after investigating roof failures in Alaska. The question is whether a layer of rigid foam on top of the panel has the potential to trap moisture and create a similar problem.Click To Enlarge

Rot in a SIP roof: Unchecked air leaks in a structural insulated panel roof can lead to decay. That was the conclusion reached by Joseph Lstiburek, a principal at the Building Science Corporation, after investigating roof failures in Alaska. The question is whether a layer of rigid foam on top of the panel has the potential to trap moisture and create a similar problem.


In Washington, D.C., Roger Lin is building a high-performance house that will incorporate structural insulated panels in the roof. In order to reduce heat losses due to thermal bridging, Lin is planning to add a 2-in. layer of expanded polystyrene foam insulation over the panels.

In a post at GreenBuildingAdvisor's Q&A forum, Lin looks for help in detailing the assembly.


More from greenbuildingadvisor.com
Green Basics: Structural Insulated Panels

Forget About Vapor Diffusion, Stop Air Leaks!

Rigid Foam Insulation

Podcast: Air Barrier vs. Vapor Barriers


But the conversation quickly turns to whether the addition of foam increases the risk of moisture accumulation and decay on the water-sensitive outer layer of oriented strand board.

On one side is GreenBuildingAdvisor senior editor Martin Holladay, who thinks the layer of foam will help reduce air leaks while keeping the the outer layer of oriented strand board on the SIPs warm. That should help keep the roof panels free or problems.

Others are convinced that trapping a layer of OSB between two materials with low permeability is a recipe for problems.

The discussion on whether Lin's approach is a good or bad idea is the topic of this week's Q&A Spotlight.

Read the whole article at Green Building Advisor

 



posted in: Blogs, roofs, SIPS

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