0 Helpful?

Spray foam ignition barrier

When one applies spray foam on the rim joist of above an unfinished basement is an "ignition barrier required? Will a 3 1/2" bat of mineral wool meet the requirement?

Asked by user-1137156
Posted Jun 11, 2014 9:38 AM ET

Tags:

4 Answers

Select your preferred way to display the comments and click "Save settings" to activate your changes.
1.

Jerry,
When spray foam is installed on the interior of a rim joists, there is no need for an ignition barrier or an thermal barrier, as long as the spray foam thickness is 3 1/4 inches or less.

If you have sprayed more than 3 1/4 inches of spray foam on your rim joist, then the foam needs to be protected by thermal barrier. For more information on acceptable thermal barriers, see Thermal Barriers and Ignition Barriers for Spray Foam.

Answered by user-756436
Posted Jun 11, 2014 10:39 AM ET
Edited Jun 11, 2014 10:41 AM ET.

2.

To answer the broader question of whether 3.5" of rock wool qualifies as a thermal barrier for foam in the cases where it's required...

...yes it does, 3" minimum. (Most spray applied cellulose qualifies at 3" or more too, but not all- you need to read the product specifications.)

Answered by user-1004076
Posted Jun 11, 2014 1:05 PM ET

3.

Dana,
Do you have a link to a document that shows that 3.5 inches of mineral wool passes the 15-minute fire test and is therefore considered equivalent to 1/2-inch drywall when used as a thermal barrier? If such a test has been conducted, is it specific to a certain brand of mineral wool?

Answered by user-756436
Posted Jun 11, 2014 1:24 PM ET
Edited Jun 11, 2014 1:25 PM ET.

4.

IIRC it takes 1.5" of generic mineral wool or fiberglass to meet the ignition barrier requirement, and 3" of generic mineral wool to meet the thermal barrier specs, but I'd have to dig to find it.

In a quick google search it seems some foam vendors think generic mineral wool qualifies at 2", but you can't always consider the words of foam guys (or me!) as gospel, eh? ;-)

http://www.foam-tech.com/theory/firebarriers.htm (see the table)

I remember seen test documentation for spray-applied rock wool that was formally tested to NFPA 275 at even less than 3" under the trade name "FireStop TB" , but couldn't find the test data page quickly on the web. It's still being advertised, but the manufacturer's website seems to be missing:

http://www.sprayfoam.com/newsarchives/archivedetails.cfm?id=776

http://www.idi-insulation.com/firestop_TD.php

Answered by user-1004076
Posted Jun 11, 2014 5:30 PM ET

Other Questions in Building Code Questions

SIP roof issues

In General questions | Asked by Matt Melton | Feb 17, 17

How do I insulate an already framed concrete wall?

In Energy efficiency and durability | Asked by Scott Thompson | Feb 10, 17

How to get notifications from comments

In General questions | Asked by Gerald Pehl | Feb 19, 17

Sealing under-layers of built-up exterior foam panel insulation

In Green building techniques | Asked by Gerald Pehl | Feb 19, 17

Passive house exterior door for reasonable price?

In Green products and materials | Asked by Matthew Michaud | Feb 4, 13
Register for a free account and join the conversation


Get a free account and join the conversation!
Become a GBA PRO!