Issue 2 - Reducing heat loss through Cavity Walls

Issue Date : 12th May 2009

Welcome to the Newry Democrat’s renewables and energy saving section brought to you by Kellys Renewable Energy Solutions (www.kellys.uk.com).

This week we shall take a look at various ways of reducing heat loss through the walls of your house, be it either a new or an existing build.  We will focus on cavity walls with various other types to follow next week.

Up to 35% of heat lost in your house is through your walls.  The most common type of wall structure in the UK and Ireland is that of a cavity wall.  We will look at the different ways of reducing heat loss through installing insulation in a cavity or solid built masonry wall.

Cavity Walls

A cavity wall consists of two single leaves of block with an air cavity situated between the two blocks with the cavity normally being 100mm in width. 

A new build would usually use 60mm of PIR (Polyisocyanurate – foil back rigid insulation) board partial fill insulation with a cavity air gap of 40mm remaining.  This air gap protects against the movement of moisture from the outside to the inside of the house.

An existing building with a cavity which has no insulation between the two leaves of block or brick may use full fill cavity insulation if feasible. 

An EPS bead (polystyrene bead) is blown into the cavity from the outside which completely fills the cavity.  The beads are uniquely designed to eliminate the transfer of moisture.

When the option of using full fill cavity insulation cannot be used, an alternative option is internal insulation which can be fixed onto the internal leaf of the cavity wall at the inside of your property.  Insulated plasterboards are fixed directly onto the internal leaf with steel fixings finished with a plaster render.