What To Do When Insulation Gets Wet

what to do when insulation gets wet

Insulation in the home can get wet for numerous reasons and you could be forgiven for thinking that you need to immediately replace it. However, what you need to do will depend on the type of insulation and whether it is able to be dried out and recover its performance after getting wet.

Water and moisture can cause problems in your home, particularly with insulated areas. Typically, the insulation that commonly gets wet is your attic insulation or loft insulation, but there are other areas where insulation can be affected by condensation, high humidity levels, roof leaks, damaged brickwork and even burst pipes.

It is therefore vital to keep all insulation materials in the home away from water and excess moisture in order to not adversely affect the insulating properties of the insulation products, making them highly ineffective and potentially requiring their replacement.

What causes dampness in insulation materials?

Insulation, as we know it, is a material used to limit heat transfer through building fabric. Showering, cooking, and other daily activities generate a lot of steam and condensation, which can become trapped within the building if proper ventilation is not provided.

Furthermore, the building’s insulation may not be breathable, preventing humidity from escaping through the walls or ceilings. When this happens, moisture becomes trapped in the insulation. There is also the possibility of dampness caused by building materials, such as plaster, being absorbed by the insulation materials.

It is pretty simple. Moisture is present in warm air. Therefore, this water has to go somewhere, right?

So, in the absence of an outlet, it reaches its dew point and settles on the insulation or the building material. Proper ventilation and adequate insulation are essential to prevent wet insulation.

What are the consequences of wet insulation?

1. The R-value:

The R-value of insulation, in simple terms, indicates how effective the material is at retaining heat within the structure. Therefore, when the R-value is higher, the insulation is better.

When your insulation gets wet, the thermal performance (R-value) decreases because the water displaces the trapped air within the insulating material. It causes the insulation to lose its insulating properties. Instead of blocking heat, it begins to transmit it. As a result, the insulation becomes ineffective, resulting in higher energy bills.

2. Mould development and air quality:

Mould is known to thrive in humid environments and appears to have a particular affinity for the UK due to the wet weather and frequent downpours. Moulds are difficult to remove once they have formed.

Moulds are harmful to your family’s health. They have been linked to respiratory problems, allergies, and even asthma. In addition, they emit an unpleasant, musty lingering odour that makes your indoors uncomfortable and lowers the air quality.

3. Damp walls cause structural damage:

You may not know if your insulation is wet or dry because it is usually hidden behind walls or beneath the floor/roof. Damp insulation is frequently detected by bubbling wallpaper, visible brown watermarks on the wall, and peeling paints. If left to its own devices, moisture can cause structural damage in the long run.

wet insulation

Do I have to replace insulation when it gets wet?

What to do when insulation gets wet depends on the type of insulation and how it reacts to moisture. A look at some of the different insulation types reveals whether your insulation getting wet is the complete disaster it might first appear.

Fibreglass Insulation

Although fibreglass insulation is resistant to moisture and is generally unaffected by it, a burst pipe or leaking roof can cause the insulation to become wet. When this happens, the water displaces the air spaces between the thin fibres, reducing their ability to insulate.

Proper ventilation in the area where fibreglass insulation is being installed, as well as the use of vapour barriers, can help to prevent moisture buildup within the insulation. Inspecting fibreglass insulation (typically pink loose-fill or batts) regularly can help detect problems with moisture and leaks early. For example, if you have wet loft insulation, remove the affected fibreglass batts and place them in a warm location so that they can dry naturally.

Once dried, reinstall the fibreglass insulation. If the smell or moisture persists, recheck the insulation in a few days as it will most likely need to be replaced.

Mineral or Rock Wool Insulation

Vapour can pass through mineral and rock wool insulation. Because it is not made of organic materials, it is moisture resistant, doesn’t soak up water and doesn’t promote the growth of mould. However, if there are leaks near the insulation, it may become wet and will need to be removed in order to dry it out so it can then regain its previous performance once completely dry.

PIR insulation or polyisocyanurate insulation

Although not waterproof, it does have some moisture-resistant properties meaning it can perform well in damp environments. However, excessive exposure to moisture or water will damage the insulation and cause its insulating performance to break down.

If it gets wet, you should remove it and then allow it to dry out naturally. Do not use any heating source or open flames to dry out the insulation.

The PIR board will in most instances regain its original insulating capacity after drying out naturally. In addition, the PIR insulation’s closed-cell structure makes drying quicker and more straightforward.

Cellulose insulation

If cellulose insulation gets wet this can be problematic. While it is usually treated to be water-resistant, it is not waterproof, so a significant leak can cause the weight of the material to increase and cause it to compress, reducing its effectiveness and thermal resistance.

It’s important to act fast if your loose fill insulation like this gets wet, as while it has some mould-resistant properties, the area it is in contact with, such as wood, does not and could therefore be affected by moisture saturation. You should sort out the cause of the wetness, such as a roof leak, and then attempt to dry out the insulation. However, if the extent of the leak is too great, you may be better off replacing the wet insulation.

Spray foam insulation

Increasingly used as a means of insulating a property, certain types of spray foam insulation can be waterproof. Closed cell foam insulation is waterproof while open cell foam insulation is not. The good news is that both types of spray foam, if they get wet, will dry out and their structure will be largely unaffected.

Dampness following loft insulation:

If you have a cold loft space for storage, heated air will most likely condense and create vapours on the insulating material. To insulate between the joists, use water-resistant mineral wool insulation.

Wet cavity wall insulation:

Dampness is not caused by cavity wall insulation. It may, however, exacerbate the problem if moisture-related problems already exist. Therefore, it is recommended that you check for such issues before installing cavity wall insulation.

If the insulation in the wall cavities was installed approximately 25 years ago, when the insulation technology was not as advanced as today, or if contractors installed the wall insulation incorrectly, condensation within the insulating material may occur causing the wall cavity material to fail.

Moisture can also enter the cavities when the external walls are wet from rainwater absorption or poor brickwork. In addition, if there is a significant temperature difference between the outer and inner walls, the warm air will condense on the insulation, causing the material in the wall cavities to become wet.

Wet insulation in a closed wall cavity will be unlikely to dry out, and in many cases, the wetness will cause the insulation to fall to the bottom where it could start to undergo mould growth.

How do you know you have water-damaged insulation?

In some instances it may be obvious that you have wet insulation, perhaps following a leak. However, it may not always be that noticeable, perhaps because the insulation is concealed, such as in cavity walls.

Some signs that indicate you might have a problem with wet insulation include:

  • Damp or musty smells
  • Mould growth and stained patches
  • Flaky paint or peeling wallpaper
  • Your property feels colder than normal


If you suspect you have a problem with wet insulation, you can investigate these issues with the help of a professional insulation expert and correct them based on their recommendations.

How do you dry out wet insulation?

As we’ve said, it is possible to dry out some type of insulation when it gets wet. The drying process for how you tackle water damaged insulation will depend on the type of insulation and the environment where the insulation is located. Where you can easily access the wet insulation, and you have sufficient crawl space, you should remove it to give you the opportunity to inspect it and see if it is worth drying out.

If you have had a noticeable leak, you should mop up the standing water from the affected area, and then use fans and dehumidifiers to dry out the area and remove moisture from the air. If it is not saturated then you can allow it to dry out naturally, but you can speed up the process using fans, but do not use excessive heat.

In circumstances where the insulation has been too obviously damaged by water or prolonged exposure, you should just replace it with new insulation.

How do you prevent wet insulation?

When it comes to keeping your insulation dry, there’s a lot to be said for keeping your property well-maintained. Roofs, guttering, plumbing, external brickwork should all be properly maintained to prevent leaks or water ingress.

If your insulation is in a loft space or attic, you should ensure that it is properly ventilated and consider the addition of a vapour or moisture barrier between your insulation and other cold surfaces to prevent moisture build-up.

As a general rule, you should always look to keep your home well-ventilated to prevent build-up of moisture. Using extractor fans in bathroom areas, dehumidifiers in problem rooms, or even just opening windows regularly, can all help to regulate moisture in the home.

Wet insulation doesn’t have to be a disaster

Wet insulation doesn’t have to be the disaster it first appears. What is key is to respond at the first signs of an issue, so inspecting your insulation regularly is key. It is possible that you could save your affected insulation by drying it out and preventing more serious issues in the home such as mould and damp which could prove costly.

Wet insulation is dangerous in the sense that it can be a breeding ground for mould growth, which can affect the health of the occupants, potentially leading to respiratory issues. Wet insulation is not only inefficient and will make your home uncomfortable to live in and more costly to heat.

If you ignore any of the signs that you have a problem with wet insulation, you’ll only be storing up future problems in your property, including moisture damage, that will end up costing you significantly more to remedy.

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