Is Spray Foam Insulation Good? An Honest UK Assessment
A balanced look at the real pros, cons, and consequences for UK homeowners
The Short Answer
Spray foam insulation offers genuine thermal benefits, but for most UK homeowners the drawbacks far outweigh the advantages.
While it excels as an insulator, spray foam creates serious problems with mortgage lenders, home insurance, property value, and roof health. The marketing rarely mentions these consequences, leaving thousands of UK homeowners facing costly removal.
Is Spray Foam Insulation Good or Bad?
Spray foam insulation is technically a high-performance product. It delivers excellent thermal resistance, creates an effective air seal, and can last for decades when correctly applied. On paper, it sounds ideal.
In practice, the real-world experience for UK homeowners tells a very different story. The UK mortgage and insurance industries have effectively rejected spray foam, and that single fact transforms what should be a home improvement into a serious financial liability.
The core problem is not the insulation performance itself. It is that spray foam applied to roof timbers blocks ventilation, prevents inspection of structural timber, and can trap moisture that leads to rot. These risks have led 70-80% of UK mortgage lenders to refuse lending on properties with spray foam insulation.
The honest verdict: spray foam is a good insulator but a bad choice for UK homes. The financial and practical consequences make it a net negative for the vast majority of homeowners.
What Are the Advantages of Spray Foam Insulation?
Spray foam does have genuine benefits, and it would be dishonest to pretend otherwise. Here is what it does well.
Genuine Benefits
Excellent Thermal Performance
Closed cell spray foam achieves R-6 to R-7 per inch, making it one of the most thermally efficient insulation materials available. Open cell achieves R-3.5 to R-3.7 per inch.
Superior Air Sealing
Spray foam expands to fill gaps, cracks, and awkward spaces that traditional insulation cannot reach. This creates an airtight seal that reduces heat loss through draughts.
Longevity
When properly installed, spray foam does not settle, sag, or lose its insulating properties over time. It can maintain performance for 20-30 years or more.
Energy Bill Reduction
Homeowners typically see a noticeable reduction in heating costs, particularly in older, draughty properties. Savings of 20-40% on heating bills are commonly reported.
Structural Reinforcement
Closed cell foam adds rigidity to the surfaces it bonds to, which can provide some additional structural support to roof timbers.
Important context: These benefits are real, but they only matter if you can keep the insulation without consequences. For most UK homeowners, the disadvantages below cancel out these advantages entirely.
What Are the Disadvantages of Spray Foam Insulation?
The disadvantages of spray foam for UK homeowners are severe and wide-ranging. These are the problems that installers rarely mention.
Serious Problems
Mortgage Rejection (70-80% of UK Lenders)
Major lenders including Nationwide, Halifax, HSBC, Santander, and Barclays refuse mortgages on properties with spray foam insulation on roof timbers. This eliminates the majority of potential buyers if you ever want to sell.
Property Value Loss of £20,000-£50,000
With most mortgage buyers excluded, your property value drops significantly. Cash buyers know you are in a weak negotiating position and offer well below market value.
Insurance Refusal or Premium Increases of 300-500%
Home insurers increasingly refuse cover for properties with spray foam, or charge dramatically higher premiums. Without valid buildings insurance, you breach mortgage conditions.
Structural Damage Risk
Spray foam blocks natural roof ventilation, trapping moisture against timbers. This can cause rot, decay, and structural weakening that remains hidden until the foam is removed.
Difficult and Expensive to Remove
Removal requires specialist manual labour and typically costs £3,000-£20,000 depending on property size and foam type. It cannot be done as a DIY project.
Prevents Timber Inspection
Surveyors cannot inspect roof timbers covered in spray foam, which is a primary reason lenders reject these properties. Hidden problems can go undetected for years.
For a more detailed look at all the issues spray foam can cause, see our comprehensive guide to the real dangers of spray foam insulation.
Spray Foam Pros vs Cons: At a Glance
| Factor | Pros | Cons |
|---|---|---|
| Thermal Performance | Excellent R-value, fills all gaps | Alternatives achieve similar results without risk |
| Mortgage Impact | None (if not on roof timbers) | 70-80% of lenders reject outright |
| Insurance | No immediate change | Refusal or 300-500% premium increase |
| Property Value | Energy efficiency appealing to some | £20,000-£50,000 value reduction typical |
| Roof Health | Keeps loft space warmer | Blocks ventilation, traps moisture, hides rot |
| Longevity | Lasts 20-30+ years | Most owners forced to remove within 5-10 years |
| Cost | £1,500-£3,500 to install | £3,000-£20,000 to remove when problems arise |
Does Spray Foam Insulation Affect Your Mortgage?
Yes, and this is the single biggest reason spray foam is a bad choice for UK homes. The mortgage issue alone makes spray foam a net negative investment for most homeowners.
What Happens in Practice
When a surveyor identifies spray foam during a mortgage valuation, the lender typically declines the mortgage application. This affects you in several ways:
- • Selling your home: Most buyers need a mortgage. If they cannot get one, they cannot buy your property. Your buyer pool shrinks to cash purchasers only.
- • Remortgaging: If you need to switch lenders for a better rate, your new lender may reject the application due to foam.
- • Equity release: Many equity release providers also reject properties with spray foam insulation.
- • Inheritance: Your beneficiaries may inherit a property they cannot mortgage or easily sell.
For a full breakdown of which lenders accept and reject spray foam, read our detailed guide on spray foam insulation and mortgage problems.
Is Open Cell or Closed Cell Spray Foam Better?
Neither type is a good choice for UK residential roofs. Both open cell and closed cell spray foam cause the same fundamental problems with mortgage lenders, insurance, and roof ventilation.
Open Cell
- • Softer, sponge-like texture
- • Absorbs water (rot risk from leaks)
- • Easier and cheaper to remove
- • Still rejected by most lenders
Closed Cell
- • Hard, rigid, plastic-like texture
- • Traps moisture behind it (hidden rot risk)
- • Much harder and more expensive to remove
- • Faces even stricter lender scrutiny
For a full comparison including removal costs for each type, see our guide on open cell vs closed cell spray foam insulation.
What Are Better Alternatives to Spray Foam Insulation?
Several insulation materials deliver strong thermal performance without the mortgage, insurance, and structural risks associated with spray foam. These alternatives are widely accepted by lenders and surveyors.
Mineral Wool (Rockwool/Glass Wool)
- • Widely available and cost-effective
- • No mortgage or insurance issues
- • Allows roof ventilation
- • Easy to install and remove
- • Good fire resistance
PIR/PUR Rigid Boards
- • High thermal performance (R-6+ per inch)
- • No lender concerns
- • Can be fitted between rafters
- • Moisture-resistant
- • Readily removable if needed
Sheep's Wool
- • Natural, sustainable material
- • Manages moisture naturally
- • No chemical off-gassing
- • Fully lender-approved
- • Good sound insulation
Blown-In Cellulose
- • Made from recycled materials
- • Fills gaps effectively
- • No mortgage implications
- • Cost-effective for loft spaces
- • Good fire and pest resistance
For detailed guidance on replacement insulation after spray foam removal, read our guide on re-insulating after spray foam removal.
What Should You Do If You Already Have Spray Foam?
If spray foam is already installed in your home, do not panic but do take action. The sooner you address it, the lower the long-term cost.
Step 1: Get a Professional Assessment
Have the foam inspected to determine the type (open or closed cell), the condition of any accessible timber, and whether there are signs of moisture problems. This assessment informs all further decisions.
Step 2: Understand Your Situation
Consider whether you plan to sell, remortgage, or stay long-term. Check your current insurance policy for exclusions related to spray foam. Read our guide on whether to remove or keep your spray foam for a detailed decision framework.
Step 3: Get Removal Quotes
If removal is the right decision, obtain quotes from specialist removal companies. Costs vary significantly based on property size, foam type, and accessibility. Always choose companies that use manual hand-tool removal, as this is the only lender-approved method.
Step 4: Re-insulate Properly
After removal, re-insulate with a lender-approved material and restore proper roof ventilation. This ensures your property regains its full value and mortgageability.
Frequently Asked Questions
Is spray foam insulation worth the money?
For UK homeowners, spray foam insulation is generally not worth the money. While the upfront installation cost of £1,500-£3,500 may seem reasonable, the potential property value loss of £20,000-£50,000, combined with mortgage rejection, insurance problems, and eventual removal costs of £3,000-£20,000, makes it a poor financial investment. Alternative insulation materials deliver comparable thermal performance without these risks.
Can you get a mortgage on a house with spray foam insulation?
It is very difficult. Around 70-80% of UK mortgage lenders reject properties with spray foam insulation applied to roof timbers. Some specialist lenders may consider it, but typically at higher interest rates and with additional conditions. In most cases, the spray foam must be professionally removed before a standard mortgage can be obtained.
Does spray foam insulation damage your roof?
Spray foam can indirectly damage your roof by blocking essential ventilation. UK roofs are designed to breathe, allowing moisture to escape. When spray foam seals the underside of the roof, moisture becomes trapped against the timber, which can lead to rot, decay, and structural weakening over time. This damage often remains hidden until the foam is removed.
How much does it cost to remove spray foam insulation in the UK?
Spray foam removal typically costs between £3,000 and £20,000 depending on your property size and the type of foam. Open cell foam removal for a 3-bed semi-detached house costs approximately £5,000-£8,000, while closed cell removal for the same property runs £7,000-£11,000. Additional costs may apply if timber repairs are needed.
Is spray foam insulation banned in the UK?
Spray foam insulation is not legally banned in the UK. However, it is effectively banned by the mortgage and insurance industries. With 70-80% of lenders rejecting it, properties with spray foam are extremely difficult to sell or remortgage. Some industry bodies, including the Property Care Association, have issued strong warnings against its use on roof timbers.
The Honest Bottom Line
Spray foam insulation is a good insulator but a bad choice for UK homes. The thermal benefits are real but completely overshadowed by the financial consequences.
If you are considering installation: choose an alternative insulation material. Mineral wool, PIR boards, and other lender-approved options provide excellent thermal performance without risking your property value, mortgage, or insurance.
If you already have spray foam: get it assessed and seriously consider professional removal. The cost of removal is a fraction of the property value you stand to lose by keeping it.
The best insulation is one that keeps your home warm AND maintains your property value. Spray foam only does the first.
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