Three of the UK’s Statutory Nature Conservation Organisations (SNCOs) – Natural England, Natural Resources Wales and Nature Scot – have taken an active part in developing recommendations for roofing membranes in bat roosts. You can find the latest guidance about which roofing membranes are suitable for use in a bat roost by clicking here.
The current advice provided through Natural England's free advice service administrated by the National Bat Helpline is that when roofing felt is to be installed in a roof that is used by bats, then only bituminous roofing felt that does not contain polypropylene/polyethylene filaments should be used. An example is bitumen felt type 1F, which is hessian reinforced. Bituminous felt is dark-coloured, with a rough surface that bats can grip onto and will help maintain a suitable and safe environment for bats within the roof structure. Sarking boards may be an alternative to bituminous felt.
Non-bitumen-coated roofing membranes (formerly known as breathable roofing membranes, modern roofing membranes, BRMs or MRMs) should not be installed into a roof that is used by bats as these are made from spun-bond polypropylene/polyethylene filaments. The long fibres that make up non-bitumen-coated roofing membranes can be pulled out by roosting bats and pose an entanglement threat to the bats. Non-bitumen-coated roofing membranes are not obligatory under any Building Regulations. Ventilation, regardless of the roofing felt used, is still required (see British Standard BS 5250:2011).
This advice provided by the National Bat Helpline is only possible thanks to the generosity of people like you. Our vital advice service helps thousands of people by providing advice for free, this in turn saves thousands of bats every year. Funding from Natural England helps cover some of our team's running costs, but it does not cover everything. Your donation will help ensure our small team can continue to provide assistance and a lifeline for bats.