All Need To Know About Insulation When Building An Extension

Cavity Wall Insulation Information

If your house was constructed before the 1920’s and survived all that Hitler’s beastly Luftwaffe could throw at it, then there is every chance that the exterior walls were built of 9 inch brickwork.

Soild enough, but about the only thing you can do to warm them up a bit, and reduce heat loss through them, is to install insulation on either the inside or outside surfaces.

Not an ideal scenario.

Cavity walls came into being around the early decades of the Twentieth Century.

Cavity Wall Construction

They are essentially 2 skins of brick or blockwork built next to each other, with a gap between them. It was first and foremost an attempt to try and stop moisture penetration, but as the years passed by, it came to people's attention that you could fill, or partially fill, the cavity in an attempt to minimise heat loss.

This became compulsory in the 1990’s. Chances are this is the method of construction that will be used on your new extension, although there are alternatives.
Have a look at your drawings.

You will see the architects’ drawings concerning the cavity details.

Which Type of Insulation?

Check out the type and thickness of insulation to be inserted by your builder as the walls go up. It may be cavity bats or slabs.

This is essentially mineral rockwool that comes in various thicknesses. Rockwool has excellent insulation properties, is cheap to produce and is excellent at preventing fire spread.

Then there is the rigid high performance thermal insulation or P.I.R. board. Everyone knows that the P stands for Polyisocyanurate.

That’s obvious.

But did you know that it is a loose translation from the ancient Arabic meaning “Oh, what a lovely warm wall” apparently. The two market leaders for this type of insulation tend to be Celotex and Kingspan.

If only they made big pants as well for that outside work in February.

Your builder should ensure that whatever insulation is chosen, it is placed uniformly and neatly into the cavity.

On most sites, you will see retaining clips that hold the Celotex or Kingspan sheets upright and prevent it falling over and bridging the cavity.

This also has the added benefit of allowing a free flow of air within the cavity itself.