New warm roof extension to an existing cold roof house

New warm roof extension to an existing cold roof house

The complexities of both Warm & Cold roof sections

This charming tile-clad property in the rural South-West was in a poor state of repair, having a complex roof with an open loft in the central part and a warm roof section at one end with a bedroom in the roof space. This warm roof section was clearly a previous extension, since the roof heights were different and it was sealed off from the main central loft. The traditional felt underlay was in a good state of repair, though there were many loose tiles; refelting was not considered necessary, so the bats’ access points remained. Because bats were known to be in the area a survey was carried out, and although there were a few very old bat droppings in the cold loft section there was no evidence of recent roosts inside, though individual bats had been observed flying under loose tiles.

The planned extension was a warm roof construction

An extension to the warm roof section was planned, extending out at right angles to the main building, adding additional bedrooms in tlx batsafe cold roof case studythe roof space, with vaulted ceilings and Velux windows in the sloping roof. Clearly the bats could not make use of the roof space here!

Compliance with building regs

Being a new extension, it had to comply with today’s current Building Regs requirements (which will become ever more stringent as we progress towards zero carbon status), and this corresponds to a considerable amount of polyurethane insulation board being fitted between the rafters. If a bitumen felt were to be used, it would require a 50 mm ventilated space beneath it and even more insulation, reducing the available headroom and making the skylight windows more awkward to fit because of its handling properties and weight.

Assessing the risk to Bats

Because there was only a risk of individual bats occasionally using the space under odd tiles, TLX Batsafe was deemed to be a suitable choice. Being a mesh-covered breather membrane, it prevents bat claws from contacting the polypropylene spunbond material (fibres of which can fluff out and entangle the bats), and conversely, prevents the breather membrane from being punctured by the bat claws. A reduced depth of insulation is required and the additional 50mm space required for ventilation with a bitumen felt is not needed.

Batsafe has been tested for resistance to bat claw abrasion (using a laboratory test devised by a bat researcher to mimic the process) and so it should not be possible for the fibres to be pulled out by their claws because of the mesh bonded to the surface. The bats can still choose whichever part of the roof they wish to spend the day in hiding under a tile, without any risk of being trapped.

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