Wet Insulation: Safety and Health Concerns

Your roof has a minor leak, but it isn’t causing any apparent damage or safety concerns – or is it? What you can’t see is that your insulation is wet and that is an expensive thing to replace, but a dangerous thing to ignore.

Your insulation sits just below your roof. Therefore, it’s the first thing to be impacted by a roof leak. Wet insulation increases the weight and burden that is put onto your roof. This can lead to warping and other structural problems. According to the American Society for Testing and Materials, water and humidity can increase the weight of insulation by 275%1.

If you have fiberglass, mineral, or wool insulation then you also need to watch out for formaldehyde. When formaldehyde gets wet or is in a place with high temperature or humidity it “off-gasses”. Off-gassing is the deterioration of a chemical. This happens with many different chemicals’ even your common crafting glue. The difference with formaldehyde is the off-gas is very dangerous and the levels of the gas declines VERY slowly, but never really reaches zero.

Formaldehyde off-gasses only during a few situations—when it’s being installed and when it’s wet or humid. So, your insulation might be okay when it’s dry, but the second that “minor” leak comes back, so do the effects.

Formaldehyde off-gas is extremely corrosive and will begin to corrode your roof and nearby structures from the inside-out. The off-gas will also slowly degrade your roof fasteners and rust your studs and wall ties. All this, not to mention the health risks! Below are the health effects at the different exposure levels. Your fiberglass insulation emission rate is 32.

No Effects

0 – 0.05 PPM

Odor Threshold

0.5 – 1.0 PPM

Neurophysiological effects

0.05 – 1.05 PPM

Eye irritation

0.05 – 2.0 PPM

Upper Respiratory Irritation

0.1 – 25 PPM

Lower airway and pulmonary effects

5.0 – 30 PPM

Pulmonary edema, pneumonia

50 – 100 PPM


100 PPM

Formaldehyde and plastics off-gas for the longest periods of time and will always return when they are exposed to leaks, high temperatures, or humidity again.

From the structural integrity of your building to the safety of the people within it—your insulation is NOT something you want to be compromised!

1 – Govan, F A, et al., editors. “Thermal Insulation, Materials, and Systems for Energy Conservation in the ’80s.” Google Books, 1983, p. 637

“The 4 Risks of Wet Roof Insulation You Can’t Ignore.” MainSource Roof Management, MainSource Roof Management, 2019