loft conversion specification

A loft conversion specification can obviously vary from property to property. However, some stipulations are valid for all. The minimum headroom on staircases and corridors is 2 metres. In circumstances where there is insufficient space to achieve this height, a minimum headroom at the centre of the stair of 1.9 metres may be acceptable. A loft conversion specification dictates that a handrail must be fitted 900 to 1000mm above the pitch line of the stairs or the floor of any landing, fitted with vertical rails. If tapered (wider stairs) or unusual staircase designs are proposed a Building Control Surveyor will need to be consulted to clarify requirements. Within a loft conversion specification, ridge vents equivalent to a continuous 5mm gap and eaves vents equivalent to a continuous 25mm gap are to be provided (front and rear); with the exception being if a breather felt is used. Ridge vents must be positioned so that they ventilate the roof space above ceiling level.

The loft conversion specification states that a vapour check layer should be provided at ceiling level to restrict the passage of water vapour from the room or rooms into the roof space and thus reduce the risk of condensation occurring. It should be ensured that there is a clear gap of at least 50mm over insulation in sloping and horizontal ceiling areas. This gap must also be maintained at the ridge. A "closed-cell" insulation, such as polyurethane board, should be used to insulate sloping ceiling areas. A loft conversion specification will insist that if the conversion involves forming a dormer, dormer cheeks within 1 metre of a boundary are to achieve at least 30 minutes fire resistance in both directions. The dormer roof is to be capable of resisting external fire spread, also for at least 30 minutes.