Cavity Wall Insulation

How much will cavity wall insulation cost?

The cost depends on the size of your house, however, with subsidies, it will usually cost £100 – £350. However, it can save up to £135 a year, so can pay for itself in 1 – 3 years.

How is cavity wall insulation installed?

Once a survey has been carried out, and your home deemed suitable for cavity wall insulation, small holes of about 22mm-25mm in diameter are drilled in a pre-determined pattern. Insulation is then blown along a flexible hose into the cavity through these holes.

Doesn’t it make a mess?

No. All work is carried out externally through small holes in the brickwork joints. A small amount of dust is created when the holes are drilled. The cavity wall insulation is then blown into place using a hose, straight into the wall, so there is no dust or spills.

How are the holes filled?

The holes used to inject the insulation are filled with matching mortar and are barely noticeable.

My house is rendered, won’t cavity wall insulation mess up the render?

The holes drilled to inject the cavity insulation are only about 22mm-25mm in diameter and are filled with mortar after the insulation has been injected. The installer will match the existing render. If the render is painted, the filled holes should be touched up with matching paint when the mortar has dried.

How long does it take to install cavity wall insulation?

Most homes can be insulated in about two hours, but larger houses may take a whole day.

How can I arrange a no-obligation survey and quote?

It’s easy! Just fill in our form here to request a survey and quote, and we’ll get back to you as soon as possible.

Doesn’t cavity wall insulation cause damp?

No. Extensive tests have shown that Knauf Supafil cavity wall insulation does not allow water to pass across the cavity. Supafil cavity wall insulation also contains a water repellent, and Knauf Supafil is approved by the BBA (British Board of Agrement). Before installing the insulation, the empty wall cavities are inspected for obstructions with a special tool called a boroscope. Any obstructions are noted and cleared by the installers before the insulation is injected.

Installations by approved installers are gauranteed by CIGA

If my house was built with a cavity, surely it’s there for a reason?

The purpose of the cavity is to prevent rain that soaks into the outside brickwork from crossing to the inside of the wall. The cavity interrupts any water that soaks through the brickwork and drains it to the bottom of the wall where it drains to the outside. Injecting mineral wool insulation into the cavity still allows water to drain to the bottom of the wall. ask the installer about Knauf Supafil cavity wall insulation, which contains a water repellent and so does not absorb water. Extensive tests have shown that Knauf Supafil cavity wall insulation does not cause water to pass across the cavity.

How do I know if I’ve got cavity walls or solid walls?

Most cavity walls are indentified by two factors.

  1. They are about 10 1/2″ to 12′ (270mm – 300mm) thick overall (You can measure this at a door opening).
  2. All the bricks visible on the outside of the wall are all 9″ (225mm) long (except at corners and openings).

Solid walls have repeat patterns of 4″ (100mm) wide bricks as well as 9″ (225mm) long bricks over the main area of the wall. The walls are usually a little over 9″ (225mm) thick, although in larger properties the walls can be 13 1/2″ (330mm) thick.

Find out more about how to tell if you have cavity walls

Can I install cavity wall insulation myself?

No. This is because specialist equipment is needed to install the insulation into the cavity and it’s important that the cavity is fully filled with the correct density of insulation. This is why only trained and approved installers are used so that a guarantee can be given.

My house is semi-detached/terraced and my neighbour(s) doesn’t want cavity wall insulation. Can you still insulate my walls?

Yes, your house can still be insulated. The installer will need to form a hole at the top and bottom of the wall to insert a spacer at the junction between the two houses. This prevents insulation being blown into the cavity of your neighbour’s house.

I’ve got a timber framed house – can I still have cavity wall insulation?

Sorry, but it’s not possible to inject cavity wall insulation into timber framed houses.

I live in a flat on the 10th floor of an apartment block, can I get cavity wall insulation?

Sorry, but it’s not practical to insulate a single flat in a block. If the property has cavity walls, the whole building should be insulated.

How can I tell if my new home’s previous owners have already insulated the cavity walls?

If a house was built within the last ten years, it probably already has cavity wall insulation, which may have been installed as slabs of insulation when the walls were built. You should have received a certificate or some form of documentation when you bought the house if it already has cavity wall insulation, so if you weren’t given one, chances are the walls need insulating. If you don’t have a certificate, though, click here to arrange a cavity wall insulation survey free of charge.

What guarantee of workmanship should I look out for in a cavity wall insulation installer?

Cavity wall insulation installers can sign up to a professional code of practice, such as those provided by the Cavity Insulation Guarantee Agency, which guarantees the work for 25 years. The installer should carry out post-installation checks on both the inside and the outside of the property, and you will be asked to sign a form to show you are happy with the work. Click here to arrange a free cavity wall insulation survey by a registered installation professional.

Are there grants available for cavity wall insulation and are there strict criteria as to who is eligible, like with loft insulation?

The cost of insulating your cavity walls has never been lower, as it can be subsidised through the CERT (Carbon Emissions Reduction Target) available from large energy suppliers, which brings the cost down to £100 – £350. This means you’ll get a return on investment in around two years’ time. Homeowners can apply for a subsidy from any of the energy suppliers regardless of whether they supply a home’s energy or not! Speak to your energy supplier about what grants and offers are available.