DIY Chatroom Home Improvement Forum

DIY Chatroom Home Improvement Forum (
-   Building & Construction (
-   -   Gaps In XPS (

drx006 06-09-2012 11:51 PM

Gaps In XPS
2 Attachment(s)
Hi I have these panels of XPS covered with OSB. The OSB is shiplaped and is a very tight fit. However the 2 inch thick XPS behind it has 1/8th gaps at the seams. Is it necessary to fill these seams if the OSB is tightly sealed over the seams. It is below grade on an interior walkout blockwall foundation that is eight feet tall. Foundation is concrete block (8 inch) with full bricks mortared on the exterior. The panels are 2 inch of XPS and about 1/2 inch of osb with shiplaped edge on the osb. It is actually all already on the walls and I was posting to see if it would be beneficial to take down the panels and seal the seams with the spray foam or just make the osb airtight. I'm worried about the 1/8 " gap letting moisture vapor through to the OSB and creating a mold issue. I don't know enough about this stuff and convection currents to know if that is a realistic concern or not. Here are some pictures.

Bob Mariani 06-10-2012 06:00 AM

Seal the gaps with spray foam. But OSB and the XPS will allow moisture to pass.

drx006 06-12-2012 11:12 PM

But OSB and the XPS will allow moisture to pass.[/QUOTE]

Thanks Bob. Does this mean that it would be ok to leave the panels alone without taking them down to seal the gaps? I was planning on putting up sheets of 1/4" wood paneling and staggering the seams over the OSB seams. If the osb seams are made airtight would that be enough to prevent any condensation mold issues in the xps gaps? How much benefit would I get from taking the panels down and sealing the gaps?

Bob Mariani 06-13-2012 04:44 AM

none.... But stopping moisture is only one part of the puzzle. Moisture will still need to move through the structure in one direction (usually towards the outside.) The joints are sealed to stop air flow. Moisture will still be transferred by diffusion. You need to have enough insulation to keep the inside plane of the outside sheathing warm enough in winter to not reach the dew point. In cold climates this is R-11 for walls In basements you need R-13 tightly against the foundation wall.

drx006 06-14-2012 12:10 AM

One more question. If I decided to take down some of the panels to fill the gaps could something like this work? Or maybe cutting strips of 2 inch thick XPS to stuff in the gaps and then covering it with the fiber mastic before putting the OSB back up.. I'm trying to avoid using alot of sprayfoam as I read it has some toxic things in it like isocyanates.

Bob Mariani 06-14-2012 07:09 PM

it will work.

drx006 06-14-2012 11:24 PM

Thanks for your help!

All times are GMT -5. The time now is 11:04 AM.

vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

Search Engine Friendly URLs by vBSEO 3.6.1