The "Dorset Model" general electrical requirements for alterations or new build thatched properties in Dorset.
Electrical Supply
If the electrical supply is from overhead lines the incoming lines must be spaced 300mm from the thatch.
RCD protection
All circuits in a thatched property should be RCD protected.
Wiring
It is possible to design electrical circuitry so that there is no wiring within the roof space, by having wall mounted instead of ceiling mounted lighting for example, and this is the best option. Do not have recessed ceiling lights on the upper floor, unless separated from the loft by 30 minutes of fire resistance, with allowance made for ventilation to prevent over-heating of the fitting. However, if wiring in the loft cannot then the following precautions are advised to minimise the likelihood of an electrical fault fire.
Squirrels, mice and rats all seem to enjoy gnawing PVC cable. Unless the loft can be made vermin free, which is difficult to guarantee with thatch, wiring should either be contained in conduit, or proof against attack itself, (e.g. steel wired armoured). Fire resisting cables are not necessarily vermin proof as they are not protected by a hard metal sheathing, (copper sheathing is comparatively soft). Metal conduit is satisfactory and good results have been reported with the use of high impact plastic pipe with a minimum diameter of 20mm. Soft plastic, or smaller diameters, would allow penetration by biting and should therefore be avoided.
Any light in the loft should be of the bulkhead or well-glass design, be sited on a central post away from the thatch and have its switch in the landing. Wiring should not be fixed to the side of rafters, to avoid possible penetration by thatching spikes/crooks, and junction boxes should be avoided so that all cable within the roof space is a continuous length.
Smoke Alarms
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The ‘Dorset Model’ has been jointly produced by the Local Authorities across Dorset in conjunction with Dorset Fire and Rescue Service, The Dorset Master Thatchers Association and after consultation with the National Inspection Council for Electrical Installation Contracting and the British Research Establishment Ltd. On the basis that evidence has shown that thatch can be made sacrificial in the event of fire.
