Does Water Soaked Wall Insulation Lose It’s R-Value?

In today’s property damage claim experiment we are going to simulate a roof leak into an insulated wall cavity to see what may happen to the insulation.

Let’s get started:

We are going to be testing two types of standard wall insulation – The wall cavity on your left is filled with what is referred to as “blown in” insulation. The wall cavity on your right contains what is termed as “batt” insulation. The wall cavities are a standard 16” on center and 3 feet high.

As we wet the blown in insulation you can clearly see how it is settling down into the lower portion of the wall cavity due to the weight of the water.

You can see that the wall cavity was filled to a height of 3 feet prior to the experiment and now has settled down to a height of only two feet. The wall cavity has settled an astounding 33%.

Once it has dried, blown in insulation is not likely to re-expand vertically back up the wall cavity and so a large portion of the wall space would remain uninsulated due to the water intrusion. If this were a standard 8’ high wall cavity then there would be approximately two and a half feet at the top of the wall that could be left completely un-insulated as a result of the water intrusion.

Now let’s see what happens when we wet the wall cavity containing the batt insulation:

The batt insulation differs from the “blown in” insulation in that it has a paper backing. This paper backing is typically stapled to the vertical studs to support it. As we wet the insulation you can see it begin to sag.

We are now one hour from the time that the insulation was first wetted and you can see that the saturated paper backing has torn under the weight of the insulation. The insulation has fallen about 7 inches from the top of the 3’ wall cavity – the equivalent of 19.4% of the height of the wall cavity. If this were a standard 8’ wall cavity then it would likely have fallen to 6.5 feet – leaving the top 1.5 feet of the wall cavity completely un-insulated.

Most of the time, it really would not matter whether the insulation fell or did not fall, because if you were aware that the insulation became wet then it should be immediately removed anyway.

However, that is the problem. When all you see is a small water stain on a ceiling that adjoins a wall then how do you know if the wall cavity got wet? Especially if the water leaked happened weeks or months ago. It is probably too late to use a moisture meter because by now the wall insulation has likely dried up – almost assuredly leaving a reservoir of mold contamination and a partially un-insulated wall cavity in its wake.

Sometimes there is not even any outward evidence that a leak has occurred such as a water stain or damage to the surface of the drywall. Water leaks inside walls can go unnoticed for any number of reasons such as having enamel paint on the walls or wallpaper or wood paneling covering the walls.

If you suspect that water has infiltrated a wall cavity and you cannot confirm it with a moisture meter because it has already dried then it may make sense to use a thermal imaging camera to check to see if the top portion of the wall cavity is at a different temperature than the lower portion. If you do not have a thermal imaging camera then an inexpensive infra-red thermometer with a laser site can be picked up at most hardware stores for around to .

And remember, if anyone tells you that the R-value of the wall insulation in a water saturated wall cavity will not be affected – you tell them to go to the youtube channel for and see it for themselves.

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