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Building Control Service Guidance Note 7 Roofspace Conversions Converting existing roof spaces can be one of the most cost effective ways of increasing living accommodation in many houses. Rooms in the roof can provide attractive internal spaces ideal for extra bedrooms, studies, playrooms, etc, with the added bonus that no garden is sacrificed for the extra space. . Is the existing roof space suitable for conversion? Some shapes and forms of roof lend themselves more readily to conversion than others. The key factors to access are the roof shape, its internal height and width, and the pitch. Gabled roofs – roofs with gable end walls are usually easier to modify to accommodate space in the roof than hipped roofs. Party or gable end walls together with any internal load – bearing walls can usually accommodate any new beams or purlins that may be required. Hipped roofs – the conversion of hipped roofs can be complicated unless internal load bearing cross walls are available or extra beams are inserted at floor level to support secondary beams or purlins. Roofs with intersecting pitches (Valleys) – Intersecting pitched roofs with valleys can also be difficult to convert unless existing internal cross walls are present to provide support for new timber beams or purlins. New columns or walls may be required at these intersections to support beams or purlins forming the new roof space. Is the type of existing roof structure suitable sor conversion? Not all types of roof structure are suitable for conversion, so it is essential to assess what type you are dealing with. Traditional rafter and purlin construction Until the 1960s most roofs to dwelling were usually made up by carpenters on site. Early roofs used large section timbers to form frames to carry purlins and rafters from these members. Most of these earlier types of roofs relied upon support from load bearing internal walls for all but the smallest spans. These roofs are often suitable for conversion. Trussed rafter roof construction Since 1945 a number of different types of prefabricated trusses have been developed. These usually do not rely on support from internal walls. The first trussed rafter roofs are normally placed at 600mm centres with the individual timber members joined together with pressed steel plates. Although it is possible to convert trussed rafter roofs it is generally more difficult than converting purlin and rafter roofs due to the lack of internal load bearing walls to support new floor constructions and the fact the trussed rafter roofs commonly have low roof pitches from 22.5o to 30o making them difficult to convert into habitable spaces. For further information, please contact the Building Control Service P O Box 102, Civic Centre, Sunderland SR2 7DN or email [email protected] Telephone 0191 561 1550 Roofspace Conversions continued Building Regulations – Building Regulation approval will always be required when a loft is converted into a habitable space. Complying with the Building Regulations The following is a general checklist for conversion works to a roof space. It is not an exhaustive list and additional items of information may be required. Structural stability (Part A) – New or altered structural members to be designed by a structural engineer. Surface spread of flame (Part B2) – Walls and ceilings to new accommodation and circulation spaces associated with the conversion must comply with the appropriate spread of flame regulations - Class 1. Fire resistance (Part B3) – This normally affects the upper floor ceiling to a new floor construction, which must achieve 30 minutes fire resistance. If the total floor area of the conversion does not exceed 50m2 and contains no more than 2 habitable rooms a modified 30 minutes standard of fire resistance to the existing 1st floor construction may be acceptable. Means of escape (Part B1) – i) In the case of a single storey house converted to two storey, emergency egress windows with an unobstructed openable area of 0.33m2 are required. The bottom of the window not to be more than 1100mm above the floor. ii) In the case of a two storey house converted to three storeys the existing stair should be enclosed with walls and doors that are fire resisting and the enclosure should either (i) extend to a final exit or (ii) give access to at least two escape routes at ground level, each delivering to final exits and separated from each other by fire resisting construction. Any glazing to the stair enclosure should be fire resisting. iii) Mains powered automatic smoke alarms should be provided to each storey level, the alarms need to be interlinked and positioned in circulation areas such as landings and halls. Sound insulation (Part E) – Existing separating walls particularly in older properties may need to be lined to achieve the minimum sound insulation required by Part E of the regulations. Ventilation of rooms (Part F1) – Windows in habitable rooms must have an opening equal to 1/20th of floor area and have controllable background ventilation of 5,000 mm2 equivalent area. Bathrooms including shower rooms require a mechanical extractor fan with minimum extract rating of 15 litres/second. Ventilation of roof space (Part F2) – Ventilation is required at eaves level equal to a continuous 25mm air – gap and at ridge level equal to a continuous 5mm air – gap. A 50mm (minimum) ventilation gap must be provided over any insulation in the pitched roof slope to ensure adequate cross ventilation. A vapour control layer is also required behind plasterboard linings to walls and sloping ceilings. Last Updated: 10th February 2011 For further information, please contact the Building Control Service P O Box 102, Civic Centre, Sunderland SR2 7DN or email [email protected] Telephone 0191 561 1550 Roofspace Conversions continued Access (Part K) – There is no restriction on the type of staircase, which may be a straight flight, winding staircase, quarter or half-landing stair. Loft ladders cannot be used to provide access to rooms although space savers alternating tread stairs may be provided if they provide access to only one habitable room. The minimum headroom for stairs to loft conversions is 1.9m to centre of stair reducing to 1.8m at side of stair. The maximum pitch of stair is 42o. Thermal insulation (Part L) – Thermal insulation is required to new walls, horizontal and sloping ceilings. Mineral wool and expanded polystyrene are often used as insulating materials. Current ‘U’ values are 0.18W/m2. K for sloping ceilings. Windows need to be double glazed and achieve a U value of 1.6 W/m².K Glazing (Part N) – Any glazing to windows lower than 800mm should be specified as safety glass (toughened or laminated). Plumbing, heating and drainage – Cisterns tanks etc may need to be raised and accommodated. Soil stacks may need to be extended to accommodate any new baths/wcs. These works need to be considered at an early stage of the project. Roofspace conversions are generally considered to be a simple procedure – this is not the case. They should be designed and constructed by people aware of the health and safety aspects affecting building occupiers. SUNDERLAND CITY COUNCIL BUILDING CONTROL SERVICE Ö Ö Ö Ö Ö Ö Ö Ö Ö Ö Ö Ö Electronic Submission of applications via www.submit-a-plan.com Quality assured procedures to BS EN ISO 9002, Qualified and experienced Building Control professionals, Commitment to customer care, Commitment to partnership and the development team approach, Free pre - submission advice, Bespoke arrangements to meet individual needs, Priority plans approval - 100% checked within 15 working days, Unrivalled local knowledge, Impartial and independent service, Same day inspection service, Free technical helpline. These are just a few examples of the ways in which Sunderland City Council Building Control Service can contribute towards a successful project. So before you build, come and talk to us. NO ONE KNOWS MORE ABOUT BUILDING IN THE CITY OF SUNDERLAND For further information, please contact the Building Control Service P O Box 102, Civic Centre, Sunderland SR2 7DN or email [email protected] Telephone 0191 561 1550