insulation in finished attic | Ask Mason Knowles - SPF Consultant | Spray Foam Technical Questions and Answers | SprayFoam Magazine Q&A Forums

Q&A Forums

Author	Comments
Andrew Tarmnel Posted: Mar 04, 2014 03:03 PM	insulation in finished attic I've been in this business for less than a year and this is the first time I've come across a spraying the roof deck because they want to finish the attic and honestly have no idea on how to complete the task while letting the house breath. I planned on using a the thermoseal 1.2lb because of its low vapor transmission properties and the rafters are 10" so I can get enough r value in them. My questions are a) can moisture escape through the paper and shingles of roof B) do I seal the vents up C) is there anyway to do it without an air exchanger. info on the house its just under 3000sqft, sealed soffits, four roof vents, built in 1900s, original windows, and fiberglass in walls
mason Posted: Mar 06, 2014 09:55 PM	Are you spraying the underside of the roof deck or the top?
mason Posted: Mar 06, 2014 09:57 PM	If spraying inside, there are many documents you can use to assist in the design. Check out Sprayfoam.org in the technical document section for paper on unvented attic assemblies. If they are finishing the attic space, I would expect to do a cathedral type ceiling. The foam sprayed between the rafters and then drywall installed over it. Yes, you seal off the soffits with some board insulation, and spraye foam to it. Make sure the kneewall you create is beyond the wall assembly so that hot air from inside the house does not escape to the underside of the roof deck. (can cause ice dams). Perform a blower door test before and after the application and that will let you know if you need to add additional ventilation. 1.2 lb foams can vary significantly in their physical properties including closed cell content and perm ratings. Best to use some hygrothermal modeling to ensure that you do not require an additiional vapor retarder with the foam in cold climates. I notice you have been spraying for a year. Have you taken any industry certification courses? I strongly recommend it. Many of the questions you asked would have been answered in the course curriculum for SPF installer certification. Also, contact me if you would like to discuss the job. 571-239-5221. First call is free.
Bob Silverman Posted: Mar 17, 2014 09:15 AM	Your foam supplier should be able to provide you with the documentation that you need and also application guidance. 1.2lb foam is still OPEN cell foam and needs to be covered with a vapor retarder in Michigan's heating climate. If your sales rep is telling you otherwise, get documentation from him to support his claims. Otherwise, you will be the one on the hook if there is an issue. Bob

Author

Comments

Andrew Tarmnel

Posted: Mar 04, 2014 03:03 PM

insulation in finished attic

I've been in this business for less than a year and this is the first time I've come across a spraying the roof deck because they want to finish the attic and honestly have no idea on how to complete the task while letting the house breath. I planned on using a the thermoseal 1.2lb because of its low vapor transmission properties and the rafters are 10" so I can get enough r value in them. My questions are a) can moisture escape through the paper and shingles of roof B) do I seal the vents up C) is there anyway to do it without an air exchanger. info on the house its just under 3000sqft, sealed soffits, four roof vents, built in 1900s, original windows, and fiberglass in walls

mason

Posted: Mar 06, 2014 09:55 PM

Are you spraying the underside of the roof deck or the top?

mason

Posted: Mar 06, 2014 09:57 PM

If spraying inside, there are many documents you can use to assist in the design. Check out Sprayfoam.org in the technical document section for paper on unvented attic assemblies. If they are finishing the attic space, I would expect to do a cathedral type ceiling. The foam sprayed between the rafters and then drywall installed over it. Yes, you seal off the soffits with some board insulation, and spraye foam to it. Make sure the kneewall you create is beyond the wall assembly so that hot air from inside the house does not escape to the underside of the roof deck. (can cause ice dams). Perform a blower door test before and after the application and that will let you know if you need to add additional ventilation. 1.2 lb foams can vary significantly in their physical properties including closed cell content and perm ratings. Best to use some hygrothermal modeling to ensure that you do not require an additiional vapor retarder with the foam in cold climates.

I notice you have been spraying for a year. Have you taken any industry certification courses? I strongly recommend it. Many of the questions you asked would have been answered in the course curriculum for SPF installer certification. Also, contact me if you would like to discuss the job. 571-239-5221. First call is free.

Bob Silverman

Posted: Mar 17, 2014 09:15 AM

Your foam supplier should be able to provide you with the documentation that you need and also application guidance. 1.2lb foam is still OPEN cell foam and needs to be covered with a vapor retarder in Michigan's heating climate. If your sales rep is telling you otherwise, get documentation from him to support his claims. Otherwise, you will be the one on the hook if there is an issue.

Bob

You need to login to reply to this topic. Please click here to login.