What Closed Cell Spray Foam Is
All spray foam starts as two liquids mixed at the nozzle. They react, expand and set within seconds. The difference between the two main types is what happens to the tiny bubbles inside as it sets.
In closed cell foam the bubbles stay sealed. The result is dense, rigid and hard to the touch — more like a firm plastic than a sponge. In open cell foam the bubbles burst open, leaving a lighter, softer material that you can usually squash with a fingertip.
Closed cell foam was sometimes chosen because it adds a little stiffness and blocks air and moisture well. Those same properties are why it's harder to remove and why surveyors want to know what the timber behind it looks like. Don’t worry about working it out — a glance or a couple of hatch photos usually tells us.
Open Cell and Closed Cell Compared
These are general tendencies. Individual installations vary, and the state of the roof underneath matters just as much as the foam.
| Open cell | Closed cell | |
|---|---|---|
| To the touch | Soft, spongy, gives under a finger | Hard and rigid |
| Weight | Light | Noticeably denser |
| Moisture behaviour | Lets some vapour pass | Holds moisture back, more like a barrier |
| Grip on the roof | Sticks, but tends to cut away more readily | Usually grips timber and felt very tightly |
| Typical removal | Quicker, still careful | Slower and more labour-intensive |
| What surveyors focus on | Hidden timbers | Hidden timbers and possible trapped moisture |
If your survey describes open cell foam, open cell spray foam removal is generally the simpler job — our spray foam insulation removal page covers it.
Why Closed Cell Foam Takes Longer
Closed cell foam rarely lets go in large pieces. It has to be cut back in sections and pared away from each rafter, purlin and strip of felt, working in a confined space and often overhead. We use a mix of hand tools and, where appropriate, powered tools, but the skill is in removing the foam without gouging the wood or pulling at the roof covering.
Where it has been sprayed straight onto slates or onto old, brittle felt, there's more chance of disturbing the covering. We’ll explain the risk beforehand and agree what will happen if repairs are needed. All of this adds time on site, which is why closed cell jobs usually sit higher in the price range.
When Closed Cell Removal Is Usually Needed
Lenders and surveyors tend to be more cautious about closed cell foam, because it can stop a roof drying out and it hides the structure completely. Removal is most often requested after a buyer's survey, during a remortgage or equity release valuation, or when there are signs of damp or timber trouble. It's still worth confirming exactly what's being asked — but where a lender says removal is a condition, closed cell foam is one of the most common reasons. Our mortgage problems page explains how to approach that conversation.
What Affects a Closed Cell Job
- Thickness of the foam and how much of the roof it covers
- What it's bonded to: timber, felt, membrane or bare slate
- Condition of the felt and slates behind it
- Roof shape and headroom, especially at hips and eaves
- Likelihood of timber or roof repairs once it's exposed
- Waste volume, re-insulation and documentation
Indicative costs
Because closed cell foam is dense and bonds tightly, removal often lands in the middle or upper part of these ranges — especially on larger or exposed roofs. Small areas of closed cell foam can still come in lower.
- A slope, a section or a little loft£1.5k – £3k
- Both slopes of an average family house£3k – £5k
- Large roofs, rigid foam or tricky access£5k – £8k+
- Measured rate£40 – £80+ a square metre
Indicative Plymouth figures only — the fixed price comes after we’ve looked at the foam in person or through good photographs. What sets the price.
Closed Cell Foam in Plymouth Homes
Closed cell foam turns up in every kind of Plymouth property. In older slate roofs around Stonehouse, Devonport and St Judes, it was sometimes sprayed partly to stop rattling or slipping slates — which means that once it's off, some slates may need refixing. In exposed spots on the Hoe or high ground in Plymstock and Roborough, where wind-driven rain is a fact of life, a closed cell layer sealing the underside of the roof is something surveyors take particular interest in.
In cramped terrace lofts, removal is slowed by the lack of space to work. In the larger roofs of Mannamead and Hartley, there's more room but simply more foam to remove.
The Removal Process
Assessment
Foam type, thickness and bonding are confirmed, along with the state of the roof covering.
Quote
The method, expected time and any risk to felt or slates are explained in writing.
Preparation
The loft is cleared and the route through the house protected.
Removal
Foam is cut back and pared from each timber, then bagged and removed.
Inspection
Exposed timbers and covering are checked and photographed.