Home/ Cavity Wall Insulation
Most cavity walls can be insulated. We check whether yours should be.
Cavity wall insulation cuts the heat your house loses through its outside walls – but only if the walls are suitable and the job is done properly. We install new cavity insulation using Energystore Superbead, and we take out existing insulation that has failed or should never have gone in.
- We look inside the cavity with a borescope before we quote
- New installs and extraction of existing insulation
- If your walls aren't right for it, we'll say so
The simple version
Your walls are a big part of where the heat goes.
Most houses built from around the 1920s onwards have cavity walls: two separate walls of masonry with a gap between them. Left empty, that gap does very little to stop heat leaving. Warmth moves from the inside wall, across the cavity, to the cold outside wall and away.
Cavity wall insulation fills the gap. Heat has a much harder time getting across, so more of it stays in the house.
How much goes through the walls? Energystore’s own figure is that an uninsulated home can lose up to 35% of its heat through them. “Up to” is doing some work there – it varies a lot from house to house – but walls are usually one of the biggest routes out.
The gap was there for a reason, though. It stops rain that soaks into the outer brickwork reaching the inside. So whatever goes into the cavity has to fill it without giving water a route across. That’s what most of this page is about.
What it actually does
Three things change when the cavity is filled properly.
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Keep more heat inside
An empty cavity lets heat move from the warm inner wall to the cold outer one. Fill it, and that route gets much harder. Rooms hold their temperature for longer after the heating clicks off.
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Use less energy to stay comfortable
Less heat escaping means less for your boiler or heat pump to replace. How much less depends on your house, your walls and how you heat it. We won't put a number on that until we've seen the property.
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Warmer inside wall surfaces
Cold walls are where condensation tends to form. Properly specified insulation keeps the inner wall warmer and can help limit that risk. It's one of the things Superbead is independently assessed for.
Thinking about a heat pump, or already have solar? Walls first is usually the cheaper order to do things in. A house that loses less heat needs a smaller system to keep it warm. The clue’s in the name.
01 · The insulation we use
Energystore Superbead. One product, chosen for how it behaves in a wet wall.
We’ve picked one cavity insulation and stuck with it. Superbead is small grey beads of expanded polystyrene, injected into the cavity with an adhesive that coats each bead as it goes in. Once it sets, the fill stays where it was put.
It’s covered by an independent Kiwa BDA Agrément, which sets out exactly how it has to be surveyed, specified and installed. We follow it. Most of the checks you’ll read about further down come straight from it.
- 0.032–0.033
- Declared thermal conductivity in W/mK, depending on the Superbead grade. Lower means less heat gets through.
- Bonded
- Beads set together so the fill resists settling and leaving gaps at the top of the wall.
- ≤ 1.0 kg/m²
- Short-term water absorption when tested to BS EN 1609.
- Extractable
- If it ever needs to come out, it can be taken out of the cavity.
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It doesn't soak water up.
The beads are closed-cell. They don't draw moisture across the cavity or up from below damp-proof course level by capillary action, which is how some older fibre insulations got into trouble.
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Water can still drain.
The small gaps between the beads let any water that gets through the outer brickwork run down inside the cavity rather than track across to the inner wall. That's what an empty cavity was designed to do, and Superbead keeps doing it.
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It fills the awkward bits.
Under window sills, between openings, above conservatories. Gaps are where cold spots start, so the drilling pattern and the equipment matter as much as the product.
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Nothing cut to size on your drive.
It goes in as a full fill, injected until the cavity is full. No boards to cut, no pile of offcuts to take away, and a shorter time on site than fitting rigid insulation.
02 · Read this bit
Does cavity wall insulation cause damp?
Done properly, in a suitable house, it shouldn't. Done badly, or in the wrong house, it can.
Plenty of homes in the UK are living with the result of the second kind. Almost every problem we see comes back to the same thing: nobody checked the house properly before the insulation went in. These are the things we check.
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How exposed the wall is.
A wall facing the prevailing weather on a hill or near the coast takes far more wind-driven rain than one in a sheltered street. Exposure has to be assessed for every wall. On the most exposed sites, some walls shouldn't be filled at all.
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The state of the outside wall.
Failed pointing, cracked render, blocked gutters and leaking downpipes all put water into the cavity. Insulate over them and the insulation gets the blame. Repairs come first.
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What's actually in the cavity.
Builders' rubble, mortar droppings and old debris can bridge the gap and carry water across. We look inside with a borescope and measure the width. For existing houses, Superbead needs a cavity of at least 40mm.
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Whether there's already a damp problem.
Condensation, a plumbing leak or a bridged damp-proof course can all look like "damp walls". Cavity insulation won't cause these or cure them. They need identifying before anything goes in.
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Whether the existing insulation is the problem.
Older insulation that has got wet, slumped or was put into an unsuitable wall can be what's carrying moisture across. Topping it up doesn't fix that. Taking it out sometimes does. More on extraction
So we look first, and we tell you what we find. If filling your walls isn’t the right call, we’d rather say so now than come back to a damp patch later.
03 · Cavity wall insulation extraction
When the insulation is the problem, it has to come out.
A lot of the UK’s cavity insulation went in under government-backed schemes, often quickly. Most of it is fine. Some of it went into walls that weren’t suitable, or was installed badly, or has since got wet and stopped doing its job.
When that happens, you can’t fix it from the outside. The old material has to be taken out, the cavity cleaned, the cause sorted – and then a decision made about what goes back in, if anything.
Signs it's worth having a look
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Damp that appeared after insulation went in
Patches on inside walls, usually on the side of the house that takes the weather.
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Mould on outside walls
Especially in corners and behind furniture, where the wall is coldest.
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Cold spots on insulated walls
Can mean the fill has slumped or was never complete, often near the top of the wall.
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Wet or compacted fill
Sometimes found when a wall is opened up for other work, or seen through a borescope.
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A survey has flagged it
A surveyor's report for a sale or remortgage has raised questions about the cavity insulation.
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It went into an exposed wall
Insulation in a wall that takes severe driving rain may never have been the right choice.
None of these prove the insulation is at fault. They're reasons to investigate before anyone starts pulling material out.
How extraction works
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Investigate
Borescope inspection, a look at the outside wall, gutters and pointing. We tell you whether extraction is actually the answer.
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Extract
Depending on the material and the wall, access is made through bricks removed at intervals or larger drill holes. Specialist vacuum and air equipment draws the old insulation out.
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Clear and check
The cavity is cleared and inspected again, so we can see what was causing the problem.
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Fix the cause
Pointing, render, gutters, debris bridging the cavity. Whatever let the water in gets dealt with, and priced separately.
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Make good, then decide
Bricks reinstated and holes made good. Then, if the wall is now suitable, we can refill with Superbead.
Sometimes the right answer is an empty cavity.
If a wall is too exposed to be filled safely, we'll recommend leaving it clear after extraction. Less insulated, but dry. That's a better outcome than doing it all again in five years.
04 · Is your house suitable?
A few things that tell us a lot.
You don’t need to work this out yourself – that’s what the assessment is for. But if you want a rough idea before you call, here’s what we look for.
Usually a good sign
- Built from roughly the 1920s onwards, with walls that have never been filled
- Brickwork in a regular pattern where every brick shows its long side
- Outside walls in decent repair: sound pointing, working gutters, no obvious cracks
- No damp problems inside at the moment
- A reasonably sheltered spot rather than an exposed hillside or seafront
Means we look harder
- Walls facing the prevailing weather on an exposed site
- Existing damp, mould or staining on inside walls
- Painted or rendered walls with cracks
- Walls that already have insulation in them
- Timber- or steel-framed houses, and walls over 12m high – different construction, different rules
A quick check you can do now
Look at your brickwork. If every brick shows its long side, it's probably a cavity wall. If short ends are dotted through the pattern, it may be a solid wall – and cavity insulation isn't the answer for that. We'll confirm either way.
05 · The process
From first look to filled walls.
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Assessment
We measure the cavity, look inside it with a borescope, check the outside walls and the exposure, and ask about any damp.
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A straight recommendation
Fill it, extract and refill, extract and leave it, or leave it alone. In writing, with a price, and with any repairs that need doing first.
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Installation
Vents sleeved, openings sealed, holes drilled in the mortar joints. The cavity is filled from the bottom up, then the holes are made good to match.
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Checks before we leave
Flues and chimneys tested to confirm they're clear, air vents checked, loft and eaves cleared of any stray beads.
The bits nobody mentions until afterwards
Blocked air bricks, beads in the loft, a flue that's been partly obstructed. These are the things that go wrong on rushed jobs. The checks in step four are required by Superbead's certification, and we do every one of them before we call the job finished.
Questions people actually ask
The short answers.
Will cavity wall insulation make my house damp?
It shouldn't, if the walls are suitable and it's installed properly. It can if the wall is very exposed, the outer brickwork is in poor condition or the cavity is full of debris. That's why we assess every wall first. The longer answer is above.
Is Superbead waterproof?
The beads don't absorb water and don't carry it across the cavity, and the gaps between them let water drain down. That's different from being a waterproof barrier. The outer wall still needs to be in reasonable condition.
How long does it last?
Superbead's certification assesses it as lasting for the life of the wall it's installed in, provided the wall is kept weathertight. It doesn't need maintaining once it's in.
Can it be taken out later if there's a problem?
Yes. Superbead can be extracted from the cavity if it ever needs to be.
I already have cavity insulation. Can you top it up?
Sometimes. If the existing fill is dry and sound but incomplete, a partial fill can top it up. If it's wet, slumped or in an unsuitable wall, topping up just adds to the problem. We'll check before suggesting either.
Does it make the wall stronger?
No, and you should be wary of anyone who says it does. The beads bond together and fill the cavity, but Superbead is insulation, not a structural product. A wall's strength comes from the brickwork, the mortar and the wall ties holding the two leaves together. Insulation doesn't replace failed wall ties or repair defective masonry. If we see signs of a structural problem during the survey, we'll tell you, and that's a job for a structural specialist before any insulation goes in.
Can you tell me exactly how much I'll save?
Not from a product data sheet, and not before we've seen the house. The finished performance of the wall depends on how it's built, how wide the cavity is, cold bridges around windows and doors, and how you heat the house. After the assessment, we can give you a much better idea for your walls specifically.
Will it block my air bricks or flue?
It shouldn't. Vents are sleeved before filling, and after installation we check air vents and test flues and chimneys to confirm they're clear.
Is there mess, and do I need to be in?
For a standard brick or block cavity wall, the work is done from outside. You'll be left with small filled holes in the mortar joints. We'll confirm timings and whether we need access inside when we quote.
Is there a guarantee?
[Guarantee details to be confirmed – provider, length and what it covers.]
No pressure. Genuinely.
If you're still just reading, that's fine – that's what the page is for. When you want someone to look at your walls properly, book an assessment. If you'd rather ask a question first, we're on the end of the phone.
New insulation, extraction, or not sure which you need – it's the same first step.