Bats Use of Buildings

At present there are 18 species of bat recognised as living in the UK. All species have at some point been found using building to roost. Some species are extremely reliant on buildings, especially during the breeding season. These species include brown long-eared bats, serotines and pipistrelles.

This reliance on buildings for roosting makes bats vulnerable to the effect of building repair work, re-roofing and timber treatments. As many suitable roosts age, they require such maintenance work and often little consideration is given to the materials used.
As many suitable roosts age, their roofs need replacing and a question regularly asked of the Bat Conservation trust is 'which breathable roofing membranes are suitable for use in bat roosts? '
This research aims to help answer this question.

For more information on bats and their use of buildings visit


Breathable Roofing Membranes

Recently, energy efficiency has come to the forefront of building regulations. Therefore, buildings are being made increasingly airtight (double glazing, better construction) and better insulated, thus houses are becoming warmer. Along with modern living (cooking, showers, central heating) the amount of water vapour in the air is also increasing. Due to increased airtightness, this water vapour travels up through the building into the roofspace, where due to cooler temperatures it can form condensation.

Traditionally the water vapour was removed through ventillation at the eaves and ridge, but increasing levels of insulation have made this difficult. The aim of a breathable roofing membrane is to allow this water vapour to escape the roofspace via the underlay itself. They have a structure that is sufficiently fine to prevent liquid water penetration, yet not too fine to prevent the transfer of water vapour.

Breathable roofing membranes are manufactured from layers of non-woven materials that are then bonded through pressure and heat. Whilst there are some differences between products all use very long polypropylene fibres to produce the external layers of the membranes. It is these fibres that have caused concern amongst bat workers.

 When Bats and BRMs meet......

Following initial surveys and talks with people in the industry three main areas of concern are being considered for research. Below is a brief synopsis of these areas, for more information please feel free to contact me.


For bat workers and others in the industry this is probably the most obvious and disturbing aspect of the research. Anecdotal evidence suggests the non-woven filaments used in the manufacture of BRMs pose an entanglement threat when used in bat roosts.

For images where entanglement has caused problems please see the images page.


Until recently the roof underlay of choice was bitumastic felt. This has very different thermal properties to the BRMs increasingly being used.

Bats are often very susceptible to changes in tempeature and humidity within their roosts and so it is important to gain an insight into the effect differing roofing materials may have upon a roofs microclimate.

 Membrane Longevity

Whilst the project was set up following reports of problems regarding the safety of bats, whilst researching the subject it has become apparent there could also be downsides for the membranes.

This project will be researching if contact with bats can reduce the functionality and therefore the service life of BRMs