Hollow Block Walls

A great majority of the houses in the greater Dublin area were built with hollow concrete blocks, sometimes called ‘cavity blocks’, because they were cheap and lighter in weight than most solid concrete blocks. The problem with them is the air spaces in the blocks contain cold air which is only 40 mm away from the inside of the house. The tops of the block walls are usually not sealed completely so air can circulate and convection currents of rising warm air ( containing heat lost from the house ) exchange places with falling currents of cold air from the eaves.  These convection currents increase the heat loss of the wall.

If the wall is insulated internally the vertical battens are fixed ( screwed or shot fired ) into the thin 40 mm layer of the block and the fibreglass insulation is only fitted between the battens. The battens and their fixings are cold bridges which ‘bring the cold’ into the house. Sometimes it is possible to see ‘pattern staining’ on painted plasterboard where the cold surface attracts condensation and stains the plasterboard finishes wherever there are battens. This effect is very clearly seen with an infrared camera. 

Walls built with hollow blocks can not be injected with insulation of any type in a way which will improve the insulating performance of the wall. The hollow sections of the blocks do not always line up vertically and the vertical cavity is often blocked by lintols, beams, mortar, broken pieces of blocks and sometimes by other construction rubbish. No one should recommend trying to inject the voids of these blocks with any kind of insulation as it is a waste of time and money.

The best solution is to instal an external insulation system which will overcome all the deficiencies of the hollow block wall if it is installed correctly and critical details are completed properly. We have developed a set of these details to ensure the external insulation system we use solves all the problems of this type of wall.