07 October 2008The Council has produced some good practice guides for people considering a loft conversion. If you require any further help please contact the Building Control section.
The following guidance is intended to give general assistance on the requirements relating to loft conversions. This guide assumes an attached, two-storey house, with a new second floor loft room. If your property differs from this example, you should seek further advice.
Note: certain requirements will not be imposed on bungalows with a loft room. More onerous requirements will be applied to three storey buildings with loft rooms.
Fire Design
Structural Considerations
General Guidance
Smoke detection
Detectors should be interlinked, mains powered with battery backup, wired to the lighting subcircuit and be installed on all three levels. Generally, detectors should be positioned over the head of the stair, on each landing.
Further details on smoke detection can be obtained from our guide on smoke detection or from the Kent Fire Safety Service.
Fire break walls and sound insulation
In the loft there should be walls separating a property from any adjacent property. This wall both prevents fire spreading between properties and also gives sound insulation. Even if an existing wall separates properties, it may need to be upgraded to give adequate sound insulation. Two possible methods are:
Two independent stud walls, with 100mm mineral fibre between and two layers of 12.5mm plasterboard each side.
Dense concrete blocks laid as a cavity or solid wall.
Even if the existing wall is solid masonry, it may need to be upgraded. Usually the heavier and denser the wall the better sound insulation provided. Sound insulation can be undermined if joints around bricks or blocks are not completely filled with mortar. Also, holes cut for electrical boxes etc. educe the thickness of the masonry and so reduce sound insulation.
Air gap insulation
A minimum of a 50mm air gap is needed over any insulation. This is to prevent a build up of condensation. Condensation encourages rot and reduces the effectiveness of insulation. A 50mm air gap and a through flow of air should prevent this.
A through flow of air must be provided by eaves ventilation the equivalent of a continuous 25mm strip, and ridge ventilation the equivalent of a continuous 5mm strip. The ventilation strip must also have a screen to stop insects from entering the roof. Care should be taken with the type of ventilation strip used. Strips usually are slotted to hold the fly screen in place. This means that a 50mm wide slotted strip will need to be used to be equivalent of a continuous 25mm wide strip. When insulation is installed, care must be taken to make sure the free flow of air is not blocked. The eaves of the existing roof may already have some ventilation. This must be checked, as it may need to be increased to achieve the requirement.
If 100mm of insulation is to be used in the sceiling (the sloping part of the roof) and the existing rafters are also 100mm, to maintain the required 50mm air gap it may be necessary to fix 50 x 50 mm battens to the back (underside) of each rafter. Alternatively, a more efficient (thinner) insulation could be used.
To help reduce potential for condensation forming in the roof space, a 500 micron-vapour barrier should be used behind the plasterboard, especially over bathrooms.
Room Ventilation
Room ventilation is required to all habitable rooms. This is to prevent and remove unpleasant living conditions. To this end, the following must be provided:
Headroom
There is no requirement regarding headroom in loft rooms (except to stairs and landings). However, headroom should be carefully considered. Floor joist sizes, allowances for deflection, decking thickness, battening of rafters, plasterboard thickness all have an effect on the overall headroom within the loft room. This may make the new loft room unusable when complete.
Stairs
Stairs must have the rise (r) and going (g) relationship (2r + g) which must be between 550mm and 700mm. The maximum pitch for a stair is 42 degrees.
Headroom on a stair and landings must be at least 2m, this can be reduced on stairs to 1.9m at the centre and 1.8m at the outside edge (but not landings). There is no minimum stair width, but a stair less than 600mm wide will be difficult to negotiate, particularly with furniture. Handrails on the stair should be between 900mm and 1100mm above the pitch line. Balusters should not allow a 100mm sphere to pass through and must not be readily climbable by children.
Glass and glazing
Any glazing on the escape route (generally, not external windows, wc’s or bathrooms) must be half hour fire resisting) normally Georgian wired glass is suitable) and must be installed with a beading system compatible with the glass used.
Any glazing (both internally and externally) including doors and windows in certain critical locations (typically low level, adjacent or in doors), must be toughened and/or be of safety glazing.
Safety Glazing
Safety glazing must be provided in doors, windows adjacent to doors and windows at low level.
Completion certificates
At the end of a satisfactory job, you will receive a Building Regulations completion certificate. Usually this is issued directly to the homeowner, or to the builder to present to the homeowner along with the final account. With either method, it is very important the completion certificate is issued. This certificate not only demonstrates that the work complies with all current Building Regulations, but also will be required in a future property sale.
