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Earnie 01-15-2012 07:31 AM

Intumescent Paint Over XPS
I read a post at a homebuilding forum where an individual was using intumescent paint to cover XPS instead of using drywall, backer board or similar to provide the thermal protection. I believe it was a crawlspace instead of a basement.

I like that idea for a crawlspace which keeps drywall out of that area.

Anyone tried this? Wondering if the XPS can still dry to the inside of the crawlspace or would the paint trap moisture?

Bob Mariani 01-15-2012 08:25 AM

you need an ignition barrier in this area not a thermal barrier. However a thermal barrier is still needed if you use the area for storage. It will still allow moisture to diffuse into the airspace of the crawlspace

Earnie 01-15-2012 08:56 AM

You may be correct Bob. I was quoting from R314 which covers Foam Plastics and specifically R314.4 Thermal Barriers. R314.5.4 does cover crawlspaces.

My crawlspace is just for utilities such as electrical wiring, plumbing, HVAC unit and ducting.

Vents are closed and sealed. Rim joist is sealed and insulated. I'm upgrading the dirt floor vapor barrier to 20 mil poly. I want to insulate the block walls with XPS but the ignition (thermal) barrier issue has me on hold. As stated, I don't want to put drywall in the crawlspace.

R314.5.4 does give other labor intensive methods for protecting the foam. The intumescent paint sounded like a good solution providing it meets the code fire rating requirement and would not trap moisture. One problem is its not listed as an approved material in R314.5.4.

Bob Mariani 01-15-2012 09:18 AM

leave a gap at the bottom of the insulation to allow water to weep out as needed. Most of the heat flow is at the top of the wall so this will not create enough heat loss to be an issue. Unless a building official is requiring this to be painted I would not worry about it. In practice the thermal protection is rarely (although this is not a good thing) addressed in a crawlspace. Myself, I use ccSPF on crawlspace walls and the fire ignition barrier is built in. It only takes about two hours to complete the work so it is my preferred method.

Earnie 01-15-2012 09:26 AM


This looks interesting but appears to not be a DIY product.

Bob Mariani 01-15-2012 10:37 AM

RIGHT. The sprayer is very high end. Another approach is to cover with FSK paper.

Earnie 01-15-2012 10:56 AM

This is getting interesting.

At one point I wanted to use foil-faced polyisocyanurate foam which would have provided the insulating properties and the foil the thermal/ignition barrier. Problem was polyisocyanurate foam absorbs moisture where as XPS does not.

So FSK paper meets the fire protection requirement over XPS but still allows moisture move through it?

Any particular brand? Does the foil come in white vs silver?

Bob Mariani 01-15-2012 11:05 AM

silver. moisture will drain to the bottom as I suggested, not though it.

AGWhitehouse 01-19-2012 09:27 AM

If you do not provide the thermal and ignition barriers specifically mentioned in the code then you will need to get specific written approval from your local code official. The sprayed on intumescent paint protection is an exception to the code and needs written approval to be considered acceptable.

Here's the exact code exerpt. Notice how it does not allow it to be left uncovered and/or painted without said approval. Also note that the foil facings on the foam are not considered approved thermal/ignition barriers as they are not listed in the approved methods noted below.


2603.4 Thermal Barrier. Except as provided for in Sections 2603.4.1 and 2603.9, foam plastic shall be seperated from the interior of the building by an approved thermal barrier of 1/2-inch (12.7mm) gypsum wallboard or equivalent thermal barrier material that will limit the average temperature rise of the unexposed surface to not more than 250degF (102degC) after 15 minutes of fire exposure, complying with the standard time-temperature curve of ASTM E 119 or UL 263. The thermal barrier shall be installed in such a manner that it will remain in place for 15 minutes based on FM 4880, UL1040, NFPA 286 or UL 1715. Combustible concealed spaces shall comply with Section 717.

2603.4.1 Thermal barrier not required. The thermal barrier specified in Section 2603.4 is not required under the conditions set forth in Sections 2603.4.1.1 through 2603.4.1.13.

(Sections 2603.4.1.1 -> 2603.4.1.5 and 2603.4.1.7 -> 2603.4.1.13 don't pertain to this topic)

2603.4.1.6 Attics and Crawl Spaces. Within an attic or crawl space where entry is made only for service of utilities, foam plastic insulation shall be protected against ignition by 1 1/2-inch-thick (38mm) mineral fiber insulation; 1/4-inch-thick (6.4mm) wood structural panel, particleboard or hardboard; 3/8-inch-thick (9.5mm) gypsum wallboard, corrosion-resistant steel having a base metal thickness of 0.016 inch (0.4mm) or other approved material installed in such a manner that the foam plastic insulation is not exposed. The protective covering shall be consistent with the requirements for the type of construction.

2603.9 Special approval. Foam plastic shall not be required to comply with the requirements of Sections 2603.4 through 2603.7 where specifically approved based on large-scale tests such as, but not limited to, NFPA 286 (with the acceptance criteria of Section 803.2), FM 4880, UL 1040 or UL 1715. Such testing shall be related to the actual end-use configuration and be performed on the finished manufactured foam plastic assembly in the maximum thickness intended for use. Foam plastics that are used as interior finish on the basis of special tests shall also conform to the flame spread requirements of Chapter 8. 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.

DavidOsgood 04-11-2017 05:00 PM

Re: Intumescent Paint Over XPS
Would BanFire work? It's an intumescent that is carried by RDR Technologies. I'm looking into it for my own house but I can't find anything on it, other than what RDR has on their website. I would feel better getting fire protection from a manufacturer I can research.

jazzop89 05-02-2017 12:39 AM

Re: Intumescent Paint Over XPS
This is exactly the thread I have been looking for! I have asked architects and GCs, and no one seems to know if I can use a simple board or foam panel substrate as a wall covering instead of drywall. I plan to redo a couple of rooms with hardwood walls and exposed brick veneer walls. I will be pulling out the drywall so I can rewire and apply SPF insulation. My policy is never to install gyp board, only to remove it because I loathe it. I thought about using hardee board or plywood with a concealed fasteners so that my walls are essentially removable hatches to make future work so simple. Or, if I can find a wall paneling that imparts an R-value, that would be optimal because I have 2x4 framing, which won't hold much insulation.

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