Spray Foam Shrinkage / Retraction

I was in one of the nicest crawl spaces I have ever been in yesterday. It was a fully encapsulated space and the owner even had a sign that said no shoes in crawlspace! Although it looked real nice in there, there appeared to be quite the shrinkage problem with the spray foam. Significant gaps had formed between the joist and the insulation.

What I plan on including in my report:
“The homes floor structure was insulated with closed cell spray foam insulation and was viewed from within the crawlspace. At numerous areas the insulation appeared to have shrunk and retracted back from the floor joist. This left a gap between the insulation and structure that will reduce the effectiveness of the insulation. The inspector recommends having this installation reviewed by a qualified insulation contractor and corrected as necessary.”

Here are the pics:

The crawlspace:

The Insulation issue:

You left out very critical piece of the information :slight_smile:

Is this unconditioned (vented to the outside) crawl space? if so, any humid air that makes it past the sprayed foam will condense on the colder surfaces from the conditioned space above and nasty things will happen (mold, rot, etc…) within matter of time. If the space is conditioned with HVAC, then those gaps are irrelevant. In fact, they have wasted $$$ on the spray foam. If conditioned with dehumidifier only, then yes, there will be mild ineffectiveness of the insulation but I wouldn’t be concerned. It wouldn’t be much worse than the energy loss via the exposed bridging of the floor joists.

Sorry. This is an unconditioned non-vented design. There is a dehumidifier plumbed in so that it is self draining and I figured that would clear up the humidity issues. The entire space is encapsulated with a very heavy moisture barrier that is properly adhered to the foundation walls. When I showed the customer I explained that it would be similar to the thermal bridging of the joists but that there may be a couple areas that just felt a little colder under foot.

As long as the dehumidifier is doing its job (there should be a hygrometer with an alarm installed to notify homeowner when humidity in the crawl goes above the dangerous level, I would put this in my report) I wouldn’t be too concerned. I wouldn’t call out further evaluation (review)… I would just note that due to shrinking of the insulation few isolated areas of the flooring may not stay as warm during the heating season and that can be improved by insulating any gaps formed due to shrinking. What exactly is a review going to tell the client? that you cannot :slight_smile: The only time an insulation guy should come out is when the homeowner decides they want more or better insulation. However, it is questionable how much warmer the floor stays with the insulation below the floor. If not warm enough, they would want to heat the crawl or install radiant floor heat. I doubt insulating those gaps would do anything noticeable. The crawl space should be properly insulated along its perimeter. I cannot tell from the pictures if this was done.

BTW, a better way to insulate the underfloor in such crawl is using rigid foam under the joists to eliminate bridging and bat insulation between the joists. But like I said, the efficiency of this in a properly insulated crawl along its perimeter is questionable. The cost of doing it vs benefit is the issue. Insulation slows transfer of energy, it does not heat the floor. If homeowner wants a heated floor, they need to do what I noted above :slight_smile:

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The foam may have misapplied (wrong “lifts”, for example).

Perfect, I guess I should have thought about that.

I do agree and I did modify my comment to remove the review and just made reference to our onsite conversation regarding the bridging.

It was. It was hard to see due to the barrier, but there was foam board all around.

Thanks for your insight, very helpful and much appreciated!

I agree. It looks like it was a difficult installation and it likely may have been too cold when they did it. I try not to get into the weeds on the why with my clients though.

^^^^^What Simon said.^^^^^

Typical/usual. Once installed, spray foam, similar to extruded foam boards, will expand and shrink over time. Both open and closed cell spray foam can and do regularly including pull away from other air barrier components.

No one has brought up the subject of wood shrinkage could be part of the situation.

Morning, Scott.
Hope this post finds you and your loved ones well.

The subject is Spray Foam Shrinkage.
It is a clean crawlspace, but will under preform.
It was a poor attempt to create an optimal Crawlspace environment. Falling grade.

Crawlspace. Poorly processed. From the grade soil to the insulation and conditioning.

1: A crawlspace requires conditioning and Venting in most areas of North America, to optimize performance.
2: The insulation should have been on the walls. Not between joist bays.
3: The spray foam applicator was not trained. Very uneven blanket.

As for the Moisture Properties of Wood. Wood is hygroscopic.
Wood moves within it’s environment, among other things durability related.
From an Article: Moisture properties of wood: Wood contracts and expands in different ways in the radial and tangential directions of the growth rings and in the direction of the grain. This phenomenon goes by the name anisotropy. As it dries, wood shrinks from being completely wet to absolutely dry, in the tangential direction by an average of 8%, in the radial direction by about 4% and in the direction of the grain by only 0.2-0.4%. Heartwood is always drier than surface wood, which makes wood drying challenging. Anisotropy and the internal tensions of wood are also caused by the warping of the wood as it dries.

The fiber-saturation point of wood, and for most species, is in the vicinity of 25% to 30% of the oven-dry/Kiln dry weight of the wood.

Very interesting subject, Scott.
Civil Engineering article. Effects of Hygroscopic Properties of Wood. Enjoy.

Here are 2 photos from yesterdays ancillary home inspection. Build. 1954. 1.5 story bungalow. Owner preparing to renovate the basement.
Heavily Checked Girder. Rear of the property.
The last girder span, roughly 7’ feet long between the last rear steel column and where wood girder entered the poured concrete foundation wall.
*Note: The wood in the concrete was visibly rotted. No probing required.
Hypotheses - Checking. The girder having reduced load-bearing capacity and saturated numerous times escalated the checking in the girder.
The rest of the girder was not checked.
There are 2 girders.
Post images as the work proceeds.

This is due to either an improper ratio of chemicals in on-site mixing, improper amount of spray foam applied at a given time, or poorly prepared surfaces (dust, damp) - or some combination of the three.Mar 21, 2012