Insulation Advice

Cavity Wall Insulation

Cavity wall insulation has been around for some 35 years now, and many of us have already had it installed, it is the single biggest energy saving measure you can have done to your home. It can save around 35% of the heat loss through your walls, and can save as much as 30% from your heating bills. It also saves around a tonne of carbon dioxide a year.

 

Cavity wall insulation is only installed by registered installers who are able to offer a 25 year guarantee with the work. The cavities will only be filled if they are suitable, and the installers will be checking the following things:

- Standard of pointing
- State of repair of bricks/render
- State of guttering
- Cavity width between 50 – 150mm
- Safe access to all external walls
- Identification of any damp issues (not condensation)
- Check for rubble in cavities
- Severe exposure to the elements

How do I know if my property has a cavity wall?

In most areas of the country properties were not built with cavity walls until around 1930, however in some areas of Dorset cavities were built as far back as around 1875, so it can be important to check your walls for a cavity.

The methods of determining whether you have a property with a cavity construction are as follows:

 

- If the walls are made up of stretcher bond bricks (bricks laid long ways side by side) then it has almost certainly got a cavity.

  

- If it has an English or Flemish bond (stretcher then header, or row of stretchers interspersed with rows of header bricks) then it is likely you have solid walls, although again this is not always the case. 

With an English or Flemish bond construction measure the width from the inside to the outside wall, if this is 10.5” or more then it should have a cavity and could be insulated.

But cavity walls were built for a reason so why fill them?

Yes cavity walls were built primarily to stop rain penetration getting onto the inside wall of the property and causing damp. The materials they use now allow the air to circulate around the cavity and keep it dry, and do not bridge the cavity in any way.

The other reason cavities were built was because of the lower build price of two separate walls compared to building one solid wall, a difference in cost of some 30% per square metre.

The companies no longer use foam to insulate cavities because although it was a good material, it was misused by some unqualified installers years ago, and this gave the industry a bad name.

Which materials do they use?

The installers use two different products to insulate the cavities depending on which is most suitable or which the installer prefers.

The first is a mineral fibre material, this is manufactured using sandstone, limestone and coke, which is melted down and spun into fibres. These fibres are ground up into loose material which is then blown into the cavities. The fibres are impregnated with an oil (usually sunflower oil), to discourage water penetration through the material. Because the fibre is loose it still allows a degree of air circulation which circulates and allows the cavity to remain dry.

The other material is a polystyrene bead product, which is blown into the cavity with an adhesive to bond it together. This material is preferred where there are external obstructions around the property, where the cavity is very wide and where the risk of water penetration is higher due to high exposure rates from the elements. Because the beads are round, if any water gets into the cavity it will roll off the poly beads to the bottom of the cavity where it will dry out.

Below are some links to the British Board of Agrement certifications for two types of these materials:

Mineral Fibre
Poly Bead
 

How long does it take to complete and what do they do?

The work on average takes around 2 – 4 hours depending on the size of the property and any obstructions (conservatories, car porches, garages). There is usually a team of two installers who will drill a series of holes in the outside wall as set out by the BBA certificates above. The drilling usually lasts between 30 minutes to an hour, and holes are drilled in between bricks or into render at approximately 1.4 metre intervals depending on the material being used.

If vents exist for the ventilation of a suspended timber floor, or for any gas or open coal fires then these will be checked to make sure the ventilation is maintained both before and after the installation.

The insulation material is then blown into the cavity until the area is filled. When the cavity is full the holes are made good using mortar between bricks or off white caulk on render.

The installers should leave the work area clean and tidy and sweep up the dust as best as possible.

So what grants can I get toward the cost?

There are grants available to everyone, some people are entitled to it free of charge and others can get a significant discount usually around 30%.

The best way of finding out what you qualify for is to phone us on:
0800 975 0166 or E-mail: info@deac.co.uk

At any time there could be several schemes available locally which mean
that you qualify to have it done free of charge when you didn’t think you would.

Other useful links:

Energy Saving Trust - Cavity wall insulation information

Energy Saving Trust - Cavity wall insulation Video

Energy Saving Trust - Best Practice guide for Cavity wall insulation in existing dwellings (Acrobat .PDF Document)

Cavity Insulation Guarantee Agency

British Board of Agrement