Floor insulation attachment

I'm wondering if anyone out there has come across specific language for the attachment of fiberglass insulation over an unconditioned crawl space. I realize there are various ways to accomplish proper installation where the insulation material makes contact with the floor diaphragm. Personally I prefer to see the use of nylon twine as a means of attachment and I'm wondering if anyone happens to know of any recommended spacing guidelines for the attachment points of a zig zag pattern of twine when used for support of floor insulation.

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Permalink Reply by James Canter on October 18, 2012 at 6:42pm

That all makes sense. Having spent the last 20 years building and remodeling homes and only the last 4 concentrating on building science and weatherization, I am still trying to figure out what many of you veterans have already learned. I thank you for the responses and your time.

Permalink Reply by Sean Lintow Sr on October 18, 2012 at 4:27pm

See section 3.2 of the ENERGY STAR TERC guidelines

From the "Retrofit Workforce Guidelines" (which are still in critical care & unavailable at the moment - but from my review)

7.36 Accessible Floors (between conditioned & unconditioned space) – personally not the best choice down south, but that’s for another day

7.36.1: Sealing the floor system will be completed before installing – very nicely stated
7.36.2: Insulation will be installed in contact with subfloor without gaps, voids, compressions, misalignments, or wind intrusions & If kraft-faced batts are used, they will be installed with kraft facing to subfloor - also very nicely stated (though kraft is worse thing you can use)
7.36.3: Batts will be secured with physical fasteners TO ensure insulation remains in contact with subfloor – the only issue is that they also need to minimize compression while still keeping it from sagging

Permalink Reply by Robert Riversong on October 18, 2012 at 4:35pm

I assume you're aware of the latest Building Science rant from Dr. Joe in which he argues against the requirement that insulation be in contact with subfloor (I excerpt it here at http://homeenergypros.lbl.gov/forum/topics/another-irreverent-whine...), and will try to get this changed in the next IRC code revision.

But why do you say that Kraft facing is a problem? It meets the IRC guideline for a 1 perm vapor retarder.

Permalink Reply by Sean Lintow Sr on October 18, 2012 at 5:14pm

Thanks Robert & yes I am but that doesn't apply to the here, now or the question posed.

As for the question about the kraft - no matter where you are at, if one is going to use such a product the last thing you want is water being trapped against it & the subfloor whether it is from moisture in the air, over active cleaners, plumbing leaks, or water splashed from tubs, showers, or sinks. Maybe you guys have less issues up north, but down here unfaced FG is bad enough & the kraft style seemingly just makes it worse

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