Thermal/Ignition barrier options?
I am looking for the best option for an ignition or thermal barrier to apply over open cell spray foam insulation in roof rafters.
My understanding is ICC code requires a minimum ignition barrier on open cell spray foam in roof rafters when the attic space functions as a usable space. I.e. – storage, air handling systems, etc.
This became a concern to me since we’ve been having to apply an intumescent (paint) coating to the open cell spray foam at the same price it would cost us to hang ½” drywall. Which didn’t make a lot of sense since the drywall is a thermal barrier not just an ignition barrier. My question is: is there a better form of achieving a barrier over open cell spray foam? By better, I mean factors builders and homeowners care about; such stronger performance, less cost, quicker ROI, etc.
One option I’m considering is a radiant foil barrier, thoughts?
*Question corresponds to climate zones 4 & 5
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Replies
Mark,
Gypsum wallboard is the way to go.
In sections R314.5.3 and R314.5.4, the IRC defines an ignition barrier as one of six permissible materials: 1 ½-inch-thick mineral fiber insulation; ¼-inch-thick wood structural panels (e.g., plywood); 3/8-inch particleboard; ¼-inch-thick hardboard; 3/8-inch-thick gypsum board; or corrosion-resistant steel having a base metal thickness of 0.016 inch.
I have never heard anyone claim that radiant barrier foil could meet the code requirement for an ignition barrier. Who suggested that it could?
check with your local inspector on code intepretation. Ignition barrier and thermal barrier are 2 different things, both can be had in a coating. But 1 costs way more then the other. If you are using it just for hvac, you will most likley be able to get away with an ingition barrier (much cheaper). we typically spec CAMAX2/ShelterShield Intumescent coating over open cell. (note, most closed cell pass as an ingition barrier without further coating). If attic is used for storage and other things, typically they will require a thermal barrier.
These guys have a video of open cell spray foams being torched. Their foam may be your answer.
http://www.envirogreeninsulation.com/what_makes_envirogreen_different.html
https://www.youtube.com/watch?v=6WUh3HDNAg0
https://www.youtube.com/watch?v=tcn-bEcZmro
https://www.youtube.com/watch?v=1Hvtz8YolC0&feature=relmfu
I generally frame in a storage area significantly smaller than the entire attic before the spray foam arrives that includes the access and a storage floor on the order of 8x16 and we sheetrock and tape the interior of that only. We don't have any mechanical systems other than some minimal duct work and wiring in the rest of the attic space and provide no access to that area or flooring.
This sets a clear delineation between the usable attic space which is floored and sheetrocked and has access, and the other space which doesn't and gets to count the ceiling drywall as the ignition barrier.
Thanks everyone for the feedback. Very helpful information.
Martin: Does IRC recognize the itumescent coating as an ignition barrier? Plus, we haven't used radiant foil as an ignition barrier. I guess my intention was more along the lines of: Because of the radiant barrier content, could we consider using it as an ignition barrier? I'll have to check with local code.
Jesse: We prefer to install closed cell, but open cell is easier to sell because of cost. At least before having to add an ignition or thermal barrier.
AJ: Looks appealing, but not getting many good reviews.
Michael: Good recommendation, do you find that space to be useful and is it more cost effective than the intumescent coating?
Thanks
Mark,
As far as I know, intumescent coatings have passed laboratory tests that have convinced some, but not all, code officials to approve them as an ignition barrier. Check with your local code official before proceeding.
Mark it seems that the sheet rocked storage areas are better and less expensive than the intumescent coatings on a number of levels.
Better because they help keep the stuff stored in there organized and clean by providing vertical walls where people can stack stuff and better lighting so they can find what they are looking for. they keep the foam from being abraded and entering the home environment as dust (with Halogenated Flame Retardants associated with endocrine disruption) but most critically they provide air control so if a fire in a wall cavity does break through to the attic it has less chance of getting oxygen it needs to keep burning. Intumescent coatings only buy you a short time on delaying ignition. controlling access to oxygen seems more likely to me to delay the spread of fire.
Less expensive because your sheet rocker is going to be there anyway, we are talking about an 8x16 ceiling and fairly short walls as it's an attic space, generally they slope from 4' to 7' and then a small bit of flat ceiling. You may want to order 8' rock and fold it in half lengthways to get it up through the access but you're just paying for a small amount of rock and plywood decking and you are getting a nice storage area rather than just code compliance. Simple to frame for so long as you remember to calculate for the thickness of the foam and sister the rafters down.
As Martin says, check with your local inspector first. Some won't accept anything less than the coatings. Some attics are too big to allow you to close off access by code.