If your attic insulation gets wet, immediately stop the source of the leak and remove any heavily saturated or clumpy material. Wet insulation loses its ability to trap heat and creates an ideal environment for mold. Most saturated insulation—especially cellulose—must be replaced rather than dried.
If your insulation has become wet, remove it as soon as possible and replace it with new insulation. Wet insulation can lose its effectiveness and can pose health risks.
What to DO if Your Attic Insulation Gets Wet
There's no one-size-fits-all answer—it depends on the insulation type, how wet it is, and airflow: Fiberglass batts may dry in a few days if just slightly damp, but heavy saturation often requires replacement. Wet cellulose insulation should be replaced. It's hard to dry out completely and breaks down quickly.
Water damage or damp – If insulation has become wet due to leaks or condensation, it loses its insulating properties and can harbour mould. Wet insulation should always be taken out and replaced to avoid health risks and structural problems.
Yes, wet insulation will mold. Mold can begin growing in damp insulation within 24 to 48 hours. Insulation itself often holds moisture against wooden subfloors or beams, creating a prime environment for mold to thrive.
Installing new insulation over old is a viable option for keeping your home warm in the winter and cool in the summer. However, the current insulation must be in good condition. It's vital that a professional insulation technician inspect your current insulation before adding another layer.
Insulating a 2,000 sq. ft. attic costs between $2,000 and $9,000, with most homeowners paying around $3,600 to $5,800 for professional installation. The wide price range depends on the type of insulation, labor rates, and whether old insulation requires removal.
Use a portable heater or fan to circulate warm air and speed up the drying process.
Short-term Exposure
The symptoms of irritation are often nonspecific, temporary, and may include itching, coughing, or wheezing. High levels of exposure to airborne fiberglass may aggravate existing asthma or bronchitis-like conditions.
Yes, a one-time water leak can absolutely cause mold. Mold spores exist naturally everywhere; if they land on a damp, porous surface (like drywall, wood, or carpet) and the moisture isn't removed quickly, mold can begin to germinate and grow within 24 to 48 hours.
Signs To Look Out For
Dark or black mould on the underside of roofing felt, rafters or boarding is a red flag. Early mould often appears as tiny black spots on timber. Discoloured or “whitish” splotches along joists and insulation lines are common too.
Keep your home adequately heated
Try to keep your home suitably heated. It usually helps to have a low background temperature of at least 15 degrees in all rooms. By doing this you are less likely to have condensation dampness as the warm air holds more moisture than cold.
Sign 1 Visible Wetness and Stains
Fresh water damage will make the insulation feel wet to the touch, while older damage leaves behind tell-tale watermarks and mineral deposits, often appearing as chalky white or yellowish-brown streaks. Different insulation types react differently.
Should I do the project myself or hire a contractor? If your attic is accessible and not too difficult to move around in, and you enjoy tackling bigger home improvement projects, attic insulating may be a good DIY project. Otherwise, consider finding a contractor to complete the project for you.
If your insulation gets wet, immediately fix the moisture source, such as a roof leak or burst pipe. Remove and replace heavily saturated cellulose or fiberglass, as wet insulation becomes heavy, sags, loses its Rcap R𝑅-value (thermal resistance), and is highly susceptible to toxic mold growth within 24−48 hours.
Mold moves faster than most people expect. Within 24 to 48 hours of moisture entering your home, mold spores can begin to germinate. Within a week, you may have visible colonies spreading across drywall, wood, and insulation.
Salt is hygroscopic, meaning it naturally attracts and absorbs moisture from the air. When placed next to a cold window pane, it can help reduce the amount of water that collects overnight — particularly in small rooms or on single-glazed windows.
Fall is an ideal time for insulation.
Adding insulation before winter can help reduce heating bills significantly. Spring is another excellent option for installation. It provides an opportunity to prepare your home for summer's heat. Insulating in spring can keep your home cooler and reduce air conditioning costs.
Attic insulation 30 years old or more, should be replaced.
After 30 years, loose-fill and blanket type attic insulation products have dramatically settled and lost much of its effectiveness. Settling reduces the R-value, which means heat will flow more easily in and out of your house.
Yes, you can spray foam your attic, but it completely changes how your attic functions. It is a highly effective air-sealing method, but it is expensive and requires careful planning.
Mice are curious and always searching for safe, snug, and warm nesting sites. Attics filled with blown-in insulation provide an excellent option–from the mice's point of view. As long as there is a ready food source. Mice are omnivorous and will eat and chew on almost anything including wood and electrical wires.
For most attics, blown insulation is better than rolled insulation. Blown-in is ideal for older homes or attics with irregular framing, as the machine-blown material conforms tightly around pipes, wires, and joists. Rolled insulation is better for brand-new, empty attics with no obstructions.
8 Signs of Poor Attic Insulation