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Masonry cavity walls in existing or new constructions can be easily filled with blown in glass mineral wool fibres, polystyrene beads or polyurethane foam. While all material have their advantages, glass mineral wool fibre is one of the most popular still among users and builders of homes. One reason may be that the insulation material is a non petroleum byproduct and therefore more eco friendly.

The popular construction method with dual walls in the envelope is wide spread in the dwellings in the northern hemisphere. Ironically most existing buildings are devoid of any insulation except for the air gap. Where ever there is insulation, the cheap material could have settled down losing it’s efficacy or else perished due to moisture and vermin. With the skyrocketed energy prices you would have been paying unnecessarily for your home heating

all these years unknowingly due to this. With the EU directives for energy rating of homes such as BER system of Ireland it has now become essential to have retrofitted (or new) cavity wall insulation in existing and new houses.

While cavity wall insulation can be applied in slabs or batts with excellent door and window seals, none is convenient and time saving as the blown-in insulation.

Equipment used and method

The cavity wall insulation of glass mineral fibre is fed into a purpose made blowing machine and injected in to the cavity under high air pressure through a flexible hose fitted with a tapered nozzle. Evenly distributed holes of size 22mm to 25mm dia will be drilled through the outer wall first to gauge the condition and properties of the existing insulation (in a retrofit).These same holes will be subsequently used for the new insulation fill.

A built in pressure transducer will sense the density and compactness of the fill to the desired settings and cut off the flow of insulation fibre and the pressurized air flow accordingly.

An important requirement is to carry out a survey before everything else and to determine the Insulation status (if any), position of flues, air vents, etc. Critical ventilation inlet/outlets such as those providing combustion oxygen or under floor ventilation, and all flues that run in the cavity wall, need to be checked and sleeves provided or else redesigned to prevent obstruction by the insulation being blown in.

An approved cavity barrier is inserted as necessary to isolate terraced or semi-detached properties and also to close all open cavities. A pattern of 22 or 25mm diameter holes are drilled in accordance with the approved code of practice as mentioned earlier. 

In new constructions, holes are generally drilled through the inner leaf (wall) to the cavity and the insulation blown in, prior to plastering. In existing buildings, holes are generally drilled through the mortar joints in the external leaf and are made good with mortar and finished to match the existing finish.

Exercise caution

A cavity wall insulation should not be considered a DIY project unless you yourself are a skilled person. In Ireland there are expert contractors who are registered with the authority SEAI (eg. Kinggroup.ie etc.) who can be employed for such projects. There are several grants for retrofits while a BER is mandatory for your new buildings. If you are keen on obtaining any of these a contractor listed with SEAI is a must.