Cavity Wall Insulation – How to Install Insulation into a Cavity Wall Yourself

Cavity wall insulation is usually done with a man made product which is used to reduce heat loss from a structure through its cavity wall construction.

In cavity wall construction there are two layers of wall constructed at equal widths apart, this itself leaves a void which is known as the cavity.

In early days of using cavity wall construction (1920’s) the cavity was thought to be enough of a barrier for damp penetration. No one really considered heat loss and this procedure continued up to 1995.

You can check what might be the case by looking at the construction method of your external brick work. If the brick’s have been laid lengthways next to each other (stretcher bond) then it would be expected to have a cavity. If the bricks have been laid length ways with alternating bricks showing their end (Flemish bond) then the wall construction is normally of solid form.

As technology increased, heat loss of a structure, now calculated with the use of (U-Values) was realised and new methods of controlling heat loss were incorporated into the construction of external cavity walls. This was achieved with the introduction of putting forms of insulation into the cavity to help with heat loss.

In older properties that have a cavity wall construction Glass Wool or Cellulose insulation was pumped or blown into the cavity. This has now been replaced with the use of pumping varying foams into the cavity to produce the effect of insulating the cavity.

With modern methods of cavity wall construction an insulation layer (cavity batt) is placed into the cavity void to increase the thermal retaining properties of the structure.

There are also weep holes built into the construction of the wall to allow any build up of moisture in the cavity tray to escape and these are normally

positioned at 450mm centres. These are little plastic grill inserts which are placed on the vertical of a course of external brick work and come in a colour range to match your brick or mortar finish.

The insulation boards are held in place by cavity wall ties. These have plastic clips which keep the insulation boards in place and are normally made of plastic coated wire or galvanized metal.

They are placed between block and brick courses in a cross formation as the wall is constructed to lock the two leaves of block/brick work together. When the insulation is placed into the cavity, the whole cavity does not need to be filled as the air void itself works as a thermal break.

Many local councils offer grants for help with the installation of cavity wall insulation. The video below shows this scheme operating in Northumberland.