Vapor Barrier Latex Paint | Ask Mason Knowles - SPF Consultant | Spray Foam Technical Questions and Answers | SprayFoam Magazine Q&A Forums

Q&A Forums

Author	Comments
JohnPeters Posted: Aug 13, 2009 08:30 AM	Vapor Barrier Latex Paint Mason, I am looking over architectural prints for a local project (Southern New England) that is calling out for a coating of vapor barrier latex paint over R-38 of open cell foam insulation that will be installed on the underside of the roof deck Have you ever heard of paint like this? Manufacturers? The roof deck consists of advantech OSB. I would think that this building material could qualify as a quasi vapor retarder. Does a double vapor retarder surrounding the foam make sense? thanks jp
Dan Beecher Posted: Aug 13, 2009 08:48 AM	I know Sherwin Williams make one. Around here the open cell guy tell their customers to spray it to the sheetrock for a vapor retarder. Saw a job they sprayed it directly to the open cell too.
SprayFoamSupply.com Posted: Aug 13, 2009 09:17 AM	TPR2 makes an intumescent that they have done the perm test on and passed. You get your ignition barrier and vapor retarder all in one step. I am not sure what brands of foam they have done the tests on though. George
mason Posted: Aug 13, 2009 11:06 AM	I wouldn't get too bogged down in the relative moisture vapor permeance of the roof sheathing material. If the material is a relative vapor retarder then you just want to reduce the amount of water vapor that can enter the open cell foam from inside the house. The acrylic coating may provide this protection, you just have to obtain the perm rating of the material at the thickness that it will be installed. You can check out the perm ratings of the coating on the material data sheet. Companies typically test their material at 20 dry mils unless otherwise noted. The thicker the applcation the lower the perm rating of the coating. So depending on the thickness and the perm rating, this coating it is possible that it may be used as a vapor retarder over the foam. As for the OSB again the material supplier should be able to provide the perm rating of the material. In sheathing this would be typically reported in the total thickness of the sheathing. So if it is 0.5 or 0.75 inches the perm rating would typically be reported in that total thickness. This is a lot different than a coating whose perm rating is based on 20 dry mils. (The thickness of a typical business card.) Depending on the overall perm rating, the OSB should allow some moisture vapor transfer through the sheathing that could into and out of the sheathing depending on the vapor drive that day or time of year. You haven't asked but you may require an ignition barrier over the foam depending on whether the foam is being covered with drywall or is in an attic space. If it is in an attic space you may be required to install an ignition barrier over the foam. I wonder if the acrylic coating was specified for that purpose as well. Check to make sure it has the proper approvals to be used as an ignition barrier. If not, then you might be advised to suggest an intumescent coating that could also provide a vapor retarder quality as suggested by NH
JohnPeters Posted: Aug 13, 2009 11:40 AM	There is an explicit request for "Latex Vapor Barrior paint" (yes, he spelled it "barrior")...however, the architect may have had his terminology mixed up when CADing these prints. The architect also has company A foam requested in the division 7 specs and he calls it company B foam on the prints. Apparently he wasn't paying attention during his AIA foam training. You bring up an excellent point regarding ignition barriers. The product that I will be spec'ing for the project is approved to be left exposed in attics per ES documentation. However, as we all know on this forum, as of June, 2010 all foam will have to be covered with an ignition or thermal barrier(unless a miracle happens). Where does this leave me as a business owner and ethical operator? Technically I can still propose this application without an ignition barrier; its not June, 2010 yet. Chances are, so will all of the people that I am bidding against. If I include an ignition barrier then I will be priced out. Again the foam is being applied to the underside of the roof deck in an unfinished attic. The architect wants a "latex" based vapor barrier paint over the foam. I do not believe that a latex based ignition barrier / vapor barrier exists. Most intumescent coatings are "water" based. Should I price this out with 2 coatings over the foam?...vapor barrier than ignition barrier? That would make me very price competitive (sarcasm)! Would that be code approved? Probably not. I think I need to talk to the architect. Thoughts? jp
mason Posted: Aug 13, 2009 03:04 PM	The latex coating that is being specified would also need to be tested with the foam to comply with building code acceptance. Some coatings are much more fire resistant than others. some help, some hurt. Check out the difference in costs between the spec as written and using another vapor retarder intumescent type coating that has approvals. You may find it is not that much difference.
Michael Fusco Posted: Aug 23, 2009 12:56 PM	Uh....guys.....I hope someone is paying very close attention to the specs....806.4 calls for a vapor barrier on the outside, top side of the roof (yep the cold side). Another vapor barrier on the bottom of the roof line would be a double vapor barrier.

Author

Comments

JohnPeters

Posted: Aug 13, 2009 08:30 AM

Vapor Barrier Latex Paint

Mason,

I am looking over architectural prints for a local project (Southern New England) that is calling out for a coating of vapor barrier latex paint over R-38 of open cell foam insulation that will be installed on the underside of the roof deck

Have you ever heard of paint like this? Manufacturers?

The roof deck consists of advantech OSB. I would think that this building material could qualify as a quasi vapor retarder. Does a double vapor retarder surrounding the foam make sense?

thanks
jp

Dan Beecher

Posted: Aug 13, 2009 08:48 AM

I know Sherwin Williams make one. Around here the open cell guy tell their customers to spray it to the sheetrock for a vapor retarder. Saw a job they sprayed it directly to the open cell too.

SprayFoamSupply.com

Posted: Aug 13, 2009 09:17 AM

TPR2 makes an intumescent that they have done the perm test on and passed. You get your ignition barrier and vapor retarder all in one step. I am not sure what brands of foam they have done the tests on though.

George

mason

Posted: Aug 13, 2009 11:06 AM

I wouldn't get too bogged down in the relative moisture vapor permeance of the roof sheathing material. If the material is a relative vapor retarder then you just want to reduce the amount of water vapor that can enter the open cell foam from inside the house. The acrylic coating may provide this protection, you just have to obtain the perm rating of the material at the thickness that it will be installed.

You can check out the perm ratings of the coating on the material data sheet. Companies typically test their material at 20 dry mils unless otherwise noted. The thicker the applcation the lower the perm rating of the coating. So depending on the thickness and the perm rating, this coating it is possible that it may be used as a vapor retarder over the foam.

As for the OSB again the material supplier should be able to provide the perm rating of the material. In sheathing this would be typically reported in the total thickness of the sheathing. So if it is 0.5 or 0.75 inches the perm rating would typically be reported in that total thickness. This is a lot different than a coating whose perm rating is based on 20 dry mils. (The thickness of a typical business card.)
Depending on the overall perm rating, the OSB should allow some moisture vapor transfer through the sheathing that could into and out of the sheathing depending on the vapor drive that day or time of year.

You haven't asked but you may require an ignition barrier over the foam depending on whether the foam is being covered with drywall or is in an attic space. If it is in an attic space you may be required to install an ignition barrier over the foam. I wonder if the acrylic coating was specified for that purpose as well. Check to make sure it has the proper approvals to be used as an ignition barrier. If not, then you might be advised to suggest an intumescent coating that could also provide a vapor retarder quality as suggested by NH

JohnPeters

Posted: Aug 13, 2009 11:40 AM

There is an explicit request for "Latex Vapor Barrior paint" (yes, he spelled it "barrior")...however, the architect may have had his terminology mixed up when CADing these prints. The architect also has company A foam requested in the division 7 specs and he calls it company B foam on the prints. Apparently he wasn't paying attention during his AIA foam training.

You bring up an excellent point regarding ignition barriers. The product that I will be spec'ing for the project is approved to be left exposed in attics per ES documentation. However, as we all know on this forum, as of June, 2010 all foam will have to be covered with an ignition or thermal barrier(unless a miracle happens). Where does this leave me as a business owner and ethical operator?

Technically I can still propose this application without an ignition barrier; its not June, 2010 yet. Chances are, so will all of the people that I am bidding against. If I include an ignition barrier then I will be priced out.

Again the foam is being applied to the underside of the roof deck in an unfinished attic.

The architect wants a "latex" based vapor barrier paint over the foam. I do not believe that a latex based ignition barrier / vapor barrier exists. Most intumescent coatings are "water" based. Should I price this out with 2 coatings over the foam?...vapor barrier than ignition barrier? That would make me very price competitive (sarcasm)! Would that be code approved? Probably not.

I think I need to talk to the architect.

Thoughts?

jp

mason

Posted: Aug 13, 2009 03:04 PM

The latex coating that is being specified would also need to be tested with the foam to comply with building code acceptance. Some coatings are much more fire resistant than others. some help, some hurt.

Check out the difference in costs between the spec as written and using another vapor retarder intumescent type coating that has approvals. You may find it is not that much difference.

Michael Fusco

Posted: Aug 23, 2009 12:56 PM

Uh....guys.....I hope someone is paying very close attention to the specs....806.4 calls for a vapor barrier on the outside, top side of the roof (yep the cold side). Another vapor barrier on the bottom of the roof line would be a double vapor barrier.

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