How-to with TLX Batsafe - scenario 2: Warm vs. Cold Roof

How-to with TLX Batsafe  - scenario 2: Warm vs. Cold Roof

Cold vs Warm roofs: where do bats roost?

A cold roof is one where there is an open loft area that may be insulated at floor level, usually with mineral wool.

A warm roof is where all of the insulation is at rafter level, either because there is a room-in-roof or because there is a vaulted ceiling with a room directly beneath (with people living there).

If it's a cold roof?Using tlx bastsafe in a cold roof

Depending on the age of the property, the roofing underlay providing waterproofing over the rafters may be a modern breather membrane, or a bitumen felt, or boarding, or nothing at all, but in nearly all cases there will be some provision for ventilation at the eaves and sometimes at the ridge or with tile vents. Ventilation is required in order to prevent condensation, which arises from water vapour migrating into the loft from the house below and encountering cold conditions. Bats may have found their way in by crawling through these ventilation holes or gaps in the underlay. If it is a derelict barn, however, larger bats may have made it their home.

Mitigation measures here would be straightforward: ensure large species requiring fly-in access have big enough entry holes, use bat access tiles if appropriate and continued eaves access, and use a roofing underlay that will not cause bats to become entangled if large numbers of them are roosting and damaging the underlay with their claws.

Using tlx batsafe in a warm roof

 If it's a warm roof?

With warm roofs, however, there would be no access to the roof space by bats as this is occupied by the homeowners! If a breather membrane is used, the rafters are completely sealed and unventilated, maximizing the insulation value. Water vapour (arising from within the house) can escape through the breathable underlay and condensation is prevented. Bats would therefore only have access under the tiles on the outside, and this would be single individuals of small species that could be accommodated in the limited space between the tile battens rather than a colony. In many such cases using a bitumen felt would seriously affect whether the target U-value could be achieved or not, as it requires there to be a 50mm ventilated space underneath to prevent condensation issues.


Using Batsafe as the roofing underlay on a warm roof means that the roofs can be properly insulated to the best possible U-value, and yet pose no danger to any bats roosting under the tiles.

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