Cavity wall insulation
It is known that bats use cavity walls as roosting sites during all seasons. The degree of importance per species and per season is difficult to discern due to the inaccessibility of the structure. Concerns about the carbon footprint of housing stock has led to even greater emphasis on having cavity walls insulated. This has given greater importance to understanding bats' use of cavity walls and identifying suitable mitigation measures where bat roosts are present.
If bats are present in a cavity wall that is scheduled to be filled with insulation a gap should be left for the bats. A difficulty is that leaving gaps in cavity wall insulation can mean that the work may not be subject to guarantee. However, the BBA (British Board of Agrément) has confirmed that partial filling of a gable wall is however allowed for blown-in EPS bead certificates, which commonly state:
3.3 Partial filling of the gable apex (i.e. limiting the fill to several brickwork courses above ceiling level) is permitted provided the top of the wall is protected by the roof and:
• the roof void is not an occupied space
• where the loft insulation is at ceiling level.
However, partial filling is outside the scope of BBA approval for blown-in mineral wool (MW) fibre certificates.
Therefore, where a bat roost is found, the property can still be insulated as per the above using EPS beads, but beware that EPS beads are installed using an adhesive, the toxicity of which to bats is not currently known.