Open cell on attic floor | Ask Mason Knowles - SPF Consultant | Spray Foam Technical Questions and Answers | SprayFoam Magazine Q&A Forums

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Dllanzy Posted: Mar 21, 2016 02:47 AM	Open cell on attic floor Hello, Recently I removed all the batt insulation from my attic due to raccoon damage from the previous owner... I was thinking about putting in spray foam to the floor of the attic but having a hard to finding out if it's a good thing to do and the proper thickness. Getting quotes that say 6in. Of open cell. That would make it a lower r value than what is required for Pittsburgh. But isn't the r value for foam different since it air seals? Is foaming the floor the smart thing to do? Thank you
mason Posted: Mar 22, 2016 08:47 AM	Sprayfoam does provide a better air seal and therefore does provide greater efficiency that typical blown in insulation. But you still need sufficient R value of insulation to be effective. 6 inches of open cell only gives you around an R 22, not enough in your area. Not to mention the open cell foam would be too easy to crush when walking around in the attic. You can spray open cell foam to the underside of the roof of the attic in an unvented attic configuration. But I would want at least an R 38 which would be around 8-10 inches (range). This is a good option if you have a lot of duct work and HVAC equipment in the attic space. You can spray closed cell foam to the floor of the attic since it has structural strength and you can walk on it. For example, I installed 4 inches of closed cell foam to the floor of my attic in Reston, VA in 2003 with 3 inches of UreK cellulose over it. This provided R 38 and the UreK provided an ignition barrier over the foam as required by building codes. For more information check out my articles at masonknowles.com on learning the difference between 1/2 lb and 2 lb SPF..
Dllanzy Posted: Mar 24, 2016 01:20 AM	Thank you... But I have asked all those questions to the contractors and they all said spray foam,since it seals, is different when it comes to r value. I guess I don't understand r value very well. Also I don't plan on going up there to after the work is done... Are they just lying to get the work at a reasonable price? I would hate to spend all this money for nothing...
mark moyer Posted: Mar 24, 2016 07:10 PM	dilanzy,,,mason nailed it...r38 minimun of no matter which product...so 10 to 12 inch of open cell. want real performance,,make it 13-15...you cant put in half as much and expect twice as much in return... the 6" bids are for fellas whom cant show you the value of a proper application, fearing the "sticker shock" will loose them the work....these are exactly the fellas you dont want workin for you....these "good enough" applications are leading to some real failure out in the world....cheap gets you cheap,,,but in the end.. we never (never say never right) apply cc foam down to a lid for a seal..yep closed cell foam is the shciznit but,,,it can get under the truss and push,,,it can make waves notice in the drywall,,,and if applied to thick will be a vapor retarding media in a ventilated systems worlds...paint blisters and other assorted goodies.. 3-4" oc foam on the flat lid...maybe more in the areas that need it...we care about the building first. we then top with 15" or so of fiberglass for a nice system that is affordable...
Dllanzy Posted: Mar 25, 2016 12:20 AM	Thanks... Can you walk on open cell to blow in fiberglass? My floor rafters are only 2x4
mark moyer Posted: Mar 25, 2016 09:58 AM	most rafter trusses are 2x4...so we fill up to the top of the chord...covering them in most places... when we blow fiber we step on the truss, not on the drywall...duh! dont forget to cap your fart fans and can lites with something before you spray so you can spray over these caps ensuring a continuous seamless layer of foam....

Author

Comments

Dllanzy

Posted: Mar 21, 2016 02:47 AM

Open cell on attic floor

Hello,
Recently I removed all the batt insulation from my attic due to raccoon damage from the previous owner... I was thinking about putting in spray foam to the floor of the attic but having a hard to finding out if it's a good thing to do and the proper thickness. Getting quotes that say 6in. Of open cell. That would make it a lower r value than what is required for Pittsburgh. But isn't the r value for foam different since it air seals? Is foaming the floor the smart thing to do? Thank you

mason

Posted: Mar 22, 2016 08:47 AM

Sprayfoam does provide a better air seal and therefore does provide greater efficiency that typical blown in insulation. But you still need sufficient R value of insulation to be effective. 6 inches of open cell only gives you around an R 22, not enough in your area. Not to mention the open cell foam would be too easy to crush when walking around in the attic.

You can spray open cell foam to the underside of the roof of the attic in an unvented attic configuration. But I would want at least an R 38 which would be around 8-10 inches (range). This is a good option if you have a lot of duct work and HVAC equipment in the attic space.

You can spray closed cell foam to the floor of the attic since it has structural strength and you can walk on it. For example, I installed 4 inches of closed cell foam to the floor of my attic in Reston, VA in 2003 with 3 inches of UreK cellulose over it. This provided R 38 and the UreK provided an ignition barrier over the foam as required by building codes.

For more information check out my articles at masonknowles.com on learning the difference between 1/2 lb and 2 lb SPF..

Dllanzy

Posted: Mar 24, 2016 01:20 AM

Thank you...
But I have asked all those questions to the contractors and they all said spray foam,since it seals, is different when it comes to r value. I guess I don't understand r value very well. Also I don't plan on going up there to after the work is done... Are they just lying to get the work at a reasonable price? I would hate to spend all this money for nothing...

mark moyer

Posted: Mar 24, 2016 07:10 PM

dilanzy,,,mason nailed it...r38 minimun of no matter which product...so 10 to 12 inch of open cell.
want real performance,,make it 13-15...you cant put in half as much and expect twice as much in return...
the 6" bids are for fellas whom cant show you the value of a proper application, fearing the "sticker shock" will loose them the work....these are exactly the fellas you dont want workin for you....these "good enough" applications are leading to some real failure out in the world....cheap gets you cheap,,,but in the end..

we never (never say never right) apply cc foam down to a lid for a seal..yep closed cell foam is the shciznit but,,,it can get under the truss and push,,,it can make waves notice in the drywall,,,and if applied to thick will be a vapor retarding media in a ventilated systems worlds...paint blisters and other assorted goodies..
3-4" oc foam on the flat lid...maybe more in the areas that need it...we care about the building first.
we then top with 15" or so of fiberglass for a nice system that is affordable...

Dllanzy

Posted: Mar 25, 2016 12:20 AM

Thanks... Can you walk on open cell to blow in fiberglass? My floor rafters are only 2x4

mark moyer

Posted: Mar 25, 2016 09:58 AM

most rafter trusses are 2x4...so we fill up to the top of the chord...covering them in most places...
when we blow fiber we step on the truss, not on the drywall...duh!
dont forget to cap your fart fans and can lites with something before you spray so you can spray over these caps ensuring a continuous seamless layer of foam....

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