Thermo Ply

Topic: 
Structural Issues
Question: 

My husband and I are hoping to build a house. The first builder we met with we noticed used Thermo ply 1/8" for the structure of the house. I questioned why plywood wasn't used, and was told that thermo ply had a better R value and was actually better then OSB or plywood. Would you build with thermo ply. I don't know why the BIA even approves this method for building it seems very cheap. Is thermo ply the new technique for building? The builder said that it doesn't cost less, but it's better and that's why they use it. I haven't signed a contract with them I am doing my research first. Thank you for your help. Your great

Answer: 

Here is my original (wrong) answer and a correction. Thank you Paul!

Thermo Ply is an insulation board with very little "shear value". It is superior to plywood or OSB as far as insulation but not as a structural component. When used in place of OSB or plywood as a side wall sheathing, some other structural component must be used to make up for the loss of shear value. One common method is the use of metal diagonal bracing.

While I have not calculated the relative cost of one system over another, I do find that plywood or OSB is used in higher priced and better built homes. I am also finding that plywood and OSB side wall and shear wall sheathing is the most common way to deal with our (Seattle) area's earthquake prone building requirements.

George.

I was wrong!, read on:

This letter is in response to comments from George Guttman with regard to Thermo Ply sheathing. The statement that Thermo Ply is not a Structural product is a gross misrepresentation of our product. While we do produce a non-structural grade (our green print), we also produce two grades that are structural (our red and blue print). Both of these grades can be used as an alternative to OSB structurally. Both have a prescriptive Evaluation report from the ICC-ES showing that they can be used as an alternative to OSB for continuous sheathing. For Engineered design, independant certifed laboratoryies have shown Red and Blue to have Allowable shear design values of 408 and 428 plf, respectively (3" O