UFFI foam insulation in an old house © Daniel FriedmanUFFI - Urea Formaldehyde Insulation Shrinkage Gaps

  • UFFI SHRINKAGE, THERMAL BYPASS LEAKS - CONTENTS: in some UFFI insulation retrofit jobs the mix & application may result in shrinkage of the foam insulation in building walls or other locations. That shrinkage opens gaps that permit air leaks or heat loss.
  • POST a QUESTION or READ FAQs about how to recognize UFFI Urea Formaldehyde Insulation in buildings and its effects on the property
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UFFI insulation shrinkage & heat loss defects:

UFFI shrinkage may reduce its effectiveness in buildings. Examining a 1970's UFFI insulation retrofit job in a New York home we observed significant shrinkage gaps at the sides and top of UFFI insulation in the building's walls. These gaps, especially in an older home, permit air leas and un-wanted heat loss, sacrificing some of the expected benefit of this spray foam insulation method.

This article series on UFFI insulation illustrates and describes UFFI - urea formaldehyde foam building insulation and describes where it is found, when it was used in buildings, how to look for it, how to distinguish this from other building foam insulation products, and its health effects. We include identification photographs and a description of a very simple field test that can immediately distinguish between 1970's vintage sprayed or pumped UFFI insulation and more contemporary icynene or polyurethane spray foam insulation jobs.

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Urea Formaldehyde Foam Insulation UFFI Shrinkage and Thermal Bypass Leaks

Shrinkage and air bypass leaks at the sides of UFFI insulation in a Poughkeepsie Home (C) Daniel FrfiedmanLook for UFFI foam spray insulation shrinkage: Neither latex foam spray insulation nor icynene foam spray insulation have the shrinkage problem of UFFI.

If you have occasion to open a building wall cavity where UFFI was installed, you'll typically see about an inch of shrinkage at each side of the foam insulation block, and you'll see a couple of inches or more of un insulated space at the top of the column of sprayed foam.

Our photo illustrates side gap shrinkage in two locations where UFFI was pumped into the walls of this Poughkeepsie New York home on the Vassar College campus. In the foreground is loose-fill cellulose insulation blowin into this attic floor. The light tan colored foam in the center of the photo is the top of UFFI that was blown into the wall cavity, most-likely durig the 1970's. You can ignore the cracked gap in the center of the foam as we can't say that that defect would be common.

But notice the significant air gap along the right side of the foam block in the wall cavity. There is about an inch of shrinkage gap between the side of the insulating foam block and the side of the wall stud.

A similar shrinkage gap is visible between the top-left side of the foam block and the sloping 2x outlook rafter at the gable end wall of this attic space.

The amount of UFFI insulation shrinkage varied from home to home and was probably the result of how precisely the product was mixed during installation, so the amount of shrinkage may vary among buildings.

An expert use of thermography or even infra-red scanning of a building exterior wall in cold weather, with the heat on indoors, may be able to detect this insulation shrinkage too.

See Formaldehyde Hazards where we describe the sources of this contaminant, exposure levels, and steps to reduce formaldehyde levels indoors.

Calculating the Loss in Building Insulation Effectiveness Due to UFFI Insulation Shrinkage

Thanks to recent correspondence from a reader, we provide this "back of the envelope" calculation of the percentage of wall area insulation lost due to UFFI insulation shrinkage. Be sure to measure your own building carefully by opening one or more wall cavities for actual examination, as the amount of UFFI shrinkage may vary significantly from one building to another.

First of all, the UFFI foam insulation shrinkage stops after the foam has fully cured. Typically within the first year or less of installation. So the problem does not continue to worsen over time.

We could calculate, even before an IR scan of the building, the total area of un insulated space in the exterior walls by examining one or two sample wall cavities to measure the actual UFFI shrinkage.

Typically, where UFFI shrinkage has occurred, we observe 2-4 inches of uninsulated space at the wall cavity top between each pair of wall studs, and about one inch of shrinkage and uninsulated space at each side of the original foam block in the stud bay. This is what we found for a Poughkeepsie NY home investigated in detail during siding renovations.

A back of the envelope calculation suggests that this means we've got roughly (3x16)+(2x96) = (48)+(192) = 240 square inches of uninsulated surface in every 16" wide x 8 foot high wall stud bay cavity (1536, or about 240/1536 = 15% of the wall cavity space is not insulated.

If you know the total square feet of wall area (subtract out windows and doors) and if you confirm that your walls were framed with studs 16" on center, you can repeat our calculation with your own UFFI shrinkage measurements. (Contact Us to send photos of what you find).

Using actual measurements from your sample cavity you could calculate the total uninsulated area for the home, and ultimately the probable heating cost savings - but beware, as we comment below, if there are other building air leaks, including thermal convection in interior partitions, the air leaks and convection losses will overwhelm even a well insulated building. More on this later.

You could add blown-in insulation around the UFFI, but it would be labor intensive as drilling to insert the new foam would need to be thoughtfully done.

We *speculate* that it would be possible to inject a new foam product, perhaps icynene, for example, at the top of the cavity - that's where the widest shrinkage will occur as it's over the whole height of the material, leaving smaller gaps at the sides - and that at least some of the new foam would run down the sides of the old material as well.

But because the old UFFI is quite fragile, very easily compressed to a powder, blowing in new foam might also, depending on its pressure, actually crush the old material, causing it to collapse, leaving a larger uninsulated hole than before you started.

Therefore what we recommend is that an owner of a UFFI insulated building should try to convince a foam insulator (probably more effective at spreading down gaps than cellulose blow in) to help me do an experiment. It's an experiment because we are not going to insulate the entire home (and pay that high cost) before we know exactly what is going to happen when foam is injected into the UFFI-insulated wall cavities.

IF we find that the addition of another insulation causes more harm than good, or does not appear cost justified, I would focus my strategy on sealing air leaks - that will give by far the most bang for the buck - see these articles for more detailed help with air leaks and building insulation retrofits. See AIR BYPASS LEAKS

Research on UFFI Shrinkage in Buildings

Article Series Contents:


Continue reading at UFFI INSULATION IMPACT ON HOME SALE PRICE or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


Or see URETHANE FOAM Deterioration, Outgassing

Or see FORMALDEHYDE GAS HAZARD REDUCTION for other measures to reduce indoor formaldehyde levels



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