Can Mould Grow Behind Spray Foam Insulation?

Spray foam insulation is often promoted as an energy-saving upgrade, especially in older homes. But beneath its clean finish lies a hidden risk that many homeowners aren't warned about: mould.

At Countrywide Roofing and Insulation, we regularly visit homes where spray foam has caused hidden issues — from damp and rot to mould and structural decay. One of the most common problems we deal with is mould growing out of sight, behind a layer of spray foam insulation.

In this post, we'll explain how and why mould can grow behind spray foam, the risks it brings, and what to do if it's already in your home.

Yes — Mould Can Grow Behind Spray Foam Insulation
To answer the question straight away: yes, mould can and does grow behind spray foam insulation.

The problem lies in how spray foam works. Especially with closed cell spray foam, it creates a rigid, airtight seal. This stops warm, moist air from escaping your loft space. If there's any condensation, roof leakage, or poor ventilation, the moisture becomes trapped — with nowhere to go.

And mould only needs two things to thrive: moisture and a surface to grow on. Once mould takes hold behind the foam, it often goes undetected for years, spreading silently while damaging timbers and creating potential health risks.

📊 Stat: Studies show around 1 in 5 homes with spray foam insulation experience damp or mould issues within five years of installation.

Why Spray Foam Creates the Perfect Conditions for Mould

Traditional loft insulation — like mineral wool — allows air to circulate. Spray foam doesn't. It alters the way your loft breathes, which is especially dangerous if it covers timber rafters or roof felt directly.

Here's what typically happens:

Spray foam traps humid air and condensation.
Moisture becomes sealed in behind the foam.
Timbers stay damp — ideal for mould growth.
The foam hides the damage, making it hard to detect.

Even open cell spray foam, which is softer and more breathable, can absorb moisture and hold it against wood or insulation layers. While not as dense, it can still create and conceal mould issues.

What Mould Behind Spray Foam Can Do to Your Home

Mould isn't just cosmetic — it's a warning sign of deeper issues. When hidden behind spray foam, it can quietly lead to:

Timber rot and weakened roof structures
Persistent damp and musty smells
Staining and ceiling damage
Unhealthy indoor air quality

Left untreated, these issues often worsen — and because the foam covers everything, many homeowners don't realise there's a problem until significant damage has occurred.

📊 Stat: Homes with sealed roof insulation systems are up to 60% more likely to develop mould compared to ventilated loft spaces.

Why Surveyors and Mortgage Lenders Are Concerned

It's not just your roof at risk — it's your home's value and mortgageability, too.

Surveyors can't assess the condition of the roof timbers when spray foam is applied directly. If there's mould, damp, or rot underneath, they won't be able to spot it. That's why many mortgage lenders refuse to approve loans on homes with spray foam insulation.

And if you're looking to sell, release equity, or remortgage — spray foam will likely hold you back until it's professionally removed and the roof is inspected.

At Countrywide Roofing and Insulation, we carry out spray foam removal — including both open cell and closed cell foam — to help restore your loft's breathability and make your home lender-friendly again.

Like Painting Over a Damp Wall

Imagine a damp patch forming on your wall. Instead of fixing the source of the moisture, you just paint over it. The problem is hidden, but it's still growing underneath. That's exactly how mould behaves when sealed behind spray foam — out of sight, but still causing damage.

What to Do If You Suspect Mould Behind Spray Foam

If you've noticed musty smells in the loft, visible damp patches, or have had spray foam applied in the past few years, it's worth getting things checked. Here's what we recommend:

1. Book an Expert Loft Assessment
We'll inspect the type of foam used and look for signs of trapped moisture or damage behind the insulation.

2. Get a Safe Spray Foam Removal Quote
We offer free, no-obligation quotes for open cell and closed cell spray foam removal, using safe, proven methods.

3. Re-Insulate with Safe, Breathable Materials
Once the foam is removed, we'll advise on the best alternative insulation that protects your roof — without trapping moisture or compromising your mortgage.

FAQs: Mould and Spray Foam Insulation

Can mould grow behind spray foam insulation?
Yes. Trapped moisture behind the foam creates a perfect environment for mould, especially when ventilation is poor.

What causes mould to grow behind the foam?
Moisture from condensation, leaks, or humid air that gets sealed in by the foam — particularly in closed cell applications.

How do I know if there's mould if I can't see it?
You might notice a musty smell, damp patches, or simply suspect something's wrong. A professional assessment can confirm it.

Does open cell foam cause mould too?
It can. Open cell foam absorbs moisture, which can lead to mould — especially if not installed with proper ventilation.

Is spray foam removal necessary to fix the problem?
Usually, yes. The foam needs to be removed to check the timbers and eliminate hidden mould properly.

Final Thoughts

Mould growing behind spray foam insulation is more common — and more harmful — than many homeowners realise. Whether you're concerned about structural damage, indoor air quality, or mortgage problems, tackling the issue early is key.

At Countrywide Roofing and Insulation, we specialise in safe, expert spray foam removal. Whether you've got open cell or closed cell foam, our team is here to help you get your loft back to a healthy, breathable, and mortgage-compliant condition.

Worried there's mould behind your spray foam insulation?

Contact Countrywide Roofing and Insulation for expert advice and a free, no-obligation quote.