Tuesday, 13 March 2012

Cavity Wall Insulation

Because we are using a traditional cavity wall construction and not something like SIPs (Sandwiched Insulated Panels), we have used an extra wide cavity, this is in order to accommodate a more effective thickness of insulation. With a cavity width of 200mm we are able to install 150mm of PIR insulation, retaining a 50mm air gap. The effectiveness of any rigid insulation is reduced at joints, so two 75mm layers have been used rather than a single layer. Using two layers allows us to stagger the vertical joints where each PIR board abuts with another within the cavity.  All remaining exposed joints are then taped, this also greatly  minimizes any air leakage.

We have

calculated that this cavity wall specification will achieve a ‘U’ value much lower than required by legislation, being almost twice as effective at reducing heat loss. PIR board insulation can also be used to line walls internaly or externaly. This may be used as a solution for insulating solid walls or timber frame structures.

A 200mm cavity requires the use of extra long wall ties which tie the inner and outer block skins together. Various types of extra long wall tie are now available. Here we are using basalt fibre based ties, which have very low thermal conductivity, this further reduces potential cold bridging.