Do I Need to Cover Foam It Green with a Vapor Barrier?
Q: Do I Need to Cover Foam It Green with a Vapor Barrier?
A: Vapor barriers, and vapor retarders are designed to reduce diffusion in your walls, and thus, prevent condensation.
You may, or may not need to cover Foam It Green with an additional vapor barrier, depending on local codes.
Water vapor, unlike condensation,is always traveling throughout your house.
When you have a window open on a humid day, when you draw a bath, or boil a pot of water, you are creating vapor.
Diffusion only accounts for 2% of water vapor movement in your home, compared with 98% due to air coming into your home from outside.
That means that insulating with a material, like spray foam, which stops air leakage will reduce the vapor in your home by nearly 100%.
Foam It Green’s closed cell foam is a Class III vapor retarder.
In many parts of the country a Class III rating qualifies as a vapor barrier, but some codes may require that you add an additional vapor barrier.
If you aren’t sure if an additional vapor barrier is required, give your local code office a call and ask them two quick questions:
- Is a vapor barrier required?
- If yes, what class of vapor retarder is required?
If a Class 1, or ‘Class II or better’ (meaning Class II or I) vapor retarder is required then you should cover the foam with kraft paper.
And remember that whether you add an additional vapor barrier or not, you have already cut down on 98% of vapor by insulating with spray foam.
Got questions about vapor barriers or other building science topics? Give us a call!
Our Project Specialists are here to help at 1-800-516-0949.
