[bubbler]

I'm cutting up Foamular 250 into 8"x14.5" rectangles to be installed as air blocking under my knee wall.

I also installed those (cheap) foam pipe covers over my heating pipes as a side project.

Just out of curiosity I took my BBQ lighter to a small wedge of each type of foam... boy they burn/melt FAST and with an acrid smell and smoke. The Foamular 250 def. had the worse smell and seemed to burn more easily than the pipe covering which seemed to melt away rather than burn.

I've seen warnings about keeping foams, like Great Stuff, away from sources of heat over 250*F (even after cured). And the foamular has a clear warning printed on it about needing to be covered by an appropriate ignition barrier.

First Question
Should I be worried about using the foamular as an air block? In my situation it is not being used as a fireblock/stop, just as an air stop. In addition the attic-side will be pressed against dense pack cellulose. I suppose any fire that makes it into the joist area would be one SERIOUS fire... but all the same, am I better off using wood for this? The reason I liked the idea of the foam was the 1) it acts as an insulator, 2) it is light weight, 3) it is cheap, 4) the most important reason, it's easy to trim and wedge into place. The perimeter of the foamular air blocks will be sealed with Great Stuff Pro Gap & Crack filler.

Second Question
I was planning to box a few IC-rated recessed lights with the foamular, I wanted to 1) keep the cellulose away from the fixture, 2) be able to air seal around the fixture (it's an air-tite rated fixture, but I figure a second air sealing foundry is a good thing). I bought LED trims to fit in, so I don't imagine that high temps will be a big issue, but you never know, for example a short or something near by could throw a spark (despite being inside a metal box). Is it a bad idea to use the foam board in this manner?

Third Question
I had been planning to air seal the attic side of my knee walls and first floor ceiling prior to putting up insulation. I am planning on spraying seams, penetrations, etc w/ Great Stuff Pro... I've seen videos of "pros" online that spray this stuff around like crazy, including on/over electric boxes. Is using Great Stuff in that manner OK, or am I risking it expanding into the box, or being a fire risk if a short occurred inside the box? Particularly with plastic Carlton boxes I feel like a real short in the box could potentially throw a spark thru the strain relief tabs that hold the romex. Maybe I'm just being overly concerned?

I get the JLC, one of the articles this month was on foam-related fires in Massachusetts... in those cases it seemed to be related to the foam catching fire on its own due to the extreme temps produced by the curing process when sprayed on too thick... but it still has me a bit worried :-/

The blown insulation contractors I hired will be here on Wed, so I need to make up my mind on what I'm doing and what materials I'm using, plus get it done ... I took Tue off work, so I will have the whole day to work on this.

[AGWhitehouse]

Under current codes, foam needs to be covered with an ignition barrier within attics and crawlspaces. Below is a code exerpt pertaining to the thermal barrier requirements.

2009 IRC excerpts:

R316.5.3 Attics. The thermal barrier specified in Section R316.4 is not required where all of the following apply:

1) Attic access is required by Section R807.1.

2) The space is entered only for purposes of repairs or maintenance.

3) The foam plastic insulation is protected against ignition using one of the following ignition barrier materials:
3.1) 1-1/2 inches (38mm) mineral fiber insulation
3.2) 1/4 inch (6.4mm) thick wood structural panels
3.3) 3/8 inch (9.5mm) particleboard
3.4) 1/4 inch(6.4mm) hardboard
3.5) 3/8 inch (9.5mm) gypsum board
3.6) Corrosion-resistant steel having a base metal thickness of 0.016 inch (0.406mm)

The above ignition barrier is not required where the foam plastic insulation has been tested in accordance with Section R316.6.

R316.6 Specific Approval. Foam plastic not meeting the requirements of Sections R316.3 through R316.5 shall be specifically approved on the basis of one of the following approved tests: NFPA 286 with the acceptance criteria of Section R302.9.4, FM4880, UL 723, UL 1040 or UL 1715, or fire tests related to actual end-use configurations. The specific approval shall be based on the actual end use configuration and shall be performed on the finished foam plastic assembly in the maximum thickness intended for use. Assemblies tested shall include seams, joints and other typical details used in the installation of the assembly and shall be tested in the manner intended for use.

[bubbler]

Would the joist bay be considered part of the attic if I have wood planks down for the floors?

Basically I will have foam board used under the knee wall in the joist bay, one side is exposed only to the joist bay between first and second floors. The other side is exposed to the joist bay in the knee wall attic, which will be filled with cellulose. The joists are covered by 1x12 planks.

So the foam is technically not exposed in the attic space itself, but rather in a joist bay.

As for the Great Stuff, using that stuff for air sealing which is then covered by FG insulation would NOT be OK?

[AGWhitehouse]

The foam is allowed within a sealed ceiling joist or stud bay. As long as the foam is covered, by a minimum of the coverings noted, so when the job is done you cannot see any foam from anywhere within the attic space.

[federer]

if foam is being sprayed to achieve 8.5inches, this means it should be done in 2 separate layers to prevent fire?

[bubbler]

Originally Posted by federer

if foam is being sprayed to achieve 8.5inches, this means it should be done in 2 separate layers to prevent fire?

See the link in my post here--

[bubbler]

Originally Posted by AGWhitehouse

The foam is allowed within a sealed ceiling joist or stud bay. As long as the foam is covered, by a minimum of the coverings noted, so when the job is done you cannot see any foam from anywhere within the attic space.

I decided to use wood. I didn't need the insulation value (since it will have blown cellulose against it... and I also found that the joist bays were almost spot on at 14.5" wide and 8" deep.

[AGWhitehouse]

Originally Posted by federer

if foam is being sprayed to achieve 8.5inches, this means it should be done in 2 separate layers to prevent fire?

If it's closed cell, 4 layers in 2" maximum lifts...

[Gary in WA]

Sounds as if you already had it done, tell us how and what materials…..

For others interested in Formular 250, etc. foamboard in an attic, if you meet certain conditions, and present your inspector with a copy of this beforehand- you may be good to go without a covering ignition barrier: 4.2.1--- http://commercial.owenscorning.com/a...579af27e5d.pdf

It’s from the same people that write the “I” codes: IRC, etc.: http://www.ncfi.com/Insulation/uploa...%20SF0608L.pdf

If they don’t buy that you can install some J.M Spider fiberglass batt insulation over it for an ignition barrier:
http://docs.google.com/viewer?a=v&q=...0hR298hcCu6EbQ.



Gary

[bubbler]

Originally Posted by GBR in WA

Sounds as if you already had it done, tell us how and what materials…..

If you're talking to me....

I decided to abandon the plan to use the Foamular 250 boards, I got worried about the potential for acrid smoke in a fire, etc--though granted there is only the equiv. of a single 4'x8' board that would have been spread around.

What I did was to buy a 4x8 sheet of 1/2" BC plywood, I cut it into strips 8" thick x 8' long, then cut that into 14.5" chunks (so I had 8"x14.5" rectangles).

I was able to wedge 80% of them into place w/ no fastners, a few were a little too large so I cut them down and a few were a little too loose so I drove four 1-5/8" sheet rock screws in to the joist to act as a back stop.

I sprayed the perimeter of each board with Great Stuff Gap & Crack sealer. The purpose of these boards is to act as an air seal under my knee wall and also as a physical stop for blown cellulose insulation to be installed later.

In hind sight the foamular would probably be fine to use in that situation, it's protected from ignition on the attic side by the cellulose and on the joist side it's surrounded by either drywall (ceiling of first floor), 2x8 wood (joists) or plywood (subfloor of second floor).

I'm not sure what to do w/ the foam I bought. I'm considering putting it against my rim joists and then covering the face w/ R13 FG as an "ignition barrier". My opinion is that it's probably less safe in that location then in the joists, but it will serve a better purpose as an air barrier there.

[AGWhitehouse]

Originally Posted by GBR in WA

you can install some J.M Spider fiberglass batt insulation over it for an ignition barrier:

For the third time, fiberglass is not an approved ignition barrier...

[bubbler]

Originally Posted by AGWhitehouse

For the third time, fiberglass is not an approved ignition barrier...

I didn't post that link, but I did read it, and according to JM it is usable as an ignition barrier......

It's the first line of linked app note "...can be used as an ignition barrier over SPF in vertical and overhead applications" ... goes on to specifically include conditioned attics and foam sheathed knee walls.

Now, maybe you believe they are incorrect in their read on the code (which would mean they are open to law suits), or maybe this is not just generic FG which is what you may be thinking of?

[federer]

this is what i mean there is like an argument to every side. it gets confusing!

[AGWhitehouse]

The code very specifically notes "mineral fiber". If that specific product meets the very specific available exceptions, then I appologize.

Point is, if you want to get around covering the foam with the very specific requirements noted in the code, go see the building official first and foremost. This code language was created for life safety issues as the foam burns FAST. You shouldn't mess around here, it could get you into a heap of trouble. Online chatrooms are no place to assume code modifications will be found acceptable.

[bubbler]

Originally Posted by federer

this is what i mean there is like an argument to every side. it gets confusing!

No kidding... and even the "pros" don't know everything.

Part of my insulation quote includes adding foam to the access doors, this foam would be sitting on the attic side of the door... I saw what he brought, noticed a foil/silver face and thought "oh good, that my be an ignition barrier"... nope, written right on the front of the foil it says "THIS IS A FLAMMABLE PRODUCT AND MUST BE PROTECTED FROM FLAMES AND IGNITION SOURCES".