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Attic Conversions Dun Laoghaire Area Committee 26th January 2015 Considering Attic Conversions The possibility of providing an attic conversion as a means of offering a solution has been considered by Dún Laoghaire Rathdown County Council. The conversion of uninhabitable roof space into habitable accommodation requires full adherence with statutory building regulations. Part A (Structure), Part B (Fire), Part F (Ventilation), Part K (stairs) and Part L (Energy) are of particular relevance to attic conversions The following information clearly illustrates that in most circumstances it is not possible to facilitate this option based on one or more technical issues Typical Roof Profile Typical roof pitch angle of 32° to 35°. Trussed rafter (more recent roofs) Headroom 35° Main ceiling joists usually 125/150x50mm. Span Building Regulations 1997 Technical Guidance Document F, Ventilation Section 1: Means of Ventilation Sub-section 1.2.1.8 states: “Ceiling height is one of a number of factors which affects ventilation of habitable rooms. The suggested dimensions in Diagram 3 are consistent with good room design, the use of standard materials and good building practice” Ventilation To achieve 2.4m clearance under the ridge the following is required :Dormer window dependent on planning permission. * a minimum span of approximately 7.5 m * at a minimum roof pitch of 35° or a minimum span of 8.4m at a roof pitch of 32° 2.4 m 35° Ceiling level minimum 2.4m above floor level (Technical Guidance Document Part F) 7.5 m Ventilation The area A in red should be at least 50% of area B in blue. The area of headroom at ceiling level (minimum of 2.4m above floor level) should be at least 50% of the area at 1.5m above floor level. This is the Technical GuidanceDocument Documents- Part Part E, This isas asinTechnical Guidance Building Regulations 1997), Diagram 5. Page 8. F (Building Regulations 2009, Diagram 3, Pg.11 A B 2.4m 1.5m Ceiling level minimum 2.4m above floor level Ventilation In typical DLR dwelling dating from 1970’s Inonwards, Cois Cairn, the illustration the as Bray,as the illustration showsshows the pitch pitch is 40° span is 7.0m. in red is 40° andand the the span is 7m. The The areaarea in red wouldbe be only approximately area would only approximately 1/4¼ of of thethe area in in blue blue. 2.4 m 1.5 m Ventilation 1.1m 2.4 m 2.0 m 35° 2.2m 2x1.1 maximum Span of approximately 8.5 m required for 2.2m wide room in attic. Prior to deeper floor joists and insulation works allowed for. Structure Typically prefabricated roof trusses are used in houses at 600mm centres. To facilitate attic conversion , the trusses need to be removed, this requires expensive alteration and replacement structural members to be inserted. Structure It is possible to use purpose designed prefabricated HOMEBOND HOUSE BUILDING MANUAL dormer trusses at design stage. Page. 181 However they involve Structure (i) extra costs "In dormer roofs the need to provide clear space (ii) may have roof height and pitch implications and of adequate width and height to accommodate (iii) planning implications rooms means that the structural form of the roof differs significantly from a conventional roof space. The design of the roof structure must take this into account, and ensure that sizing and disposition of members is adequate". Structure Insulation to be inserted to building regulations standard between and under rafters. The typical headroom here before inserting new floor joists at a pitch angle of 35° and a span of 7.0m, is 2.2m, at 32° pitch it is smaller. After inserting new floor joists in lieu of ceiling joists this figure is reduced. Trusses strengthened with extra members Main ceiling joists not strong enough to support floor loads of attic room. New stronger deeper floor joists have to be inserted. Equipment and Services Services and equipment that may have to be altered, relocated or replaced - chimney stack - flues -gas boiler etc. - water storage - electrical cabling/trunking, equipment - ventilation/extraction ducting Access Existing staircase with landings TYPICAL SECTION TYPICAL FIRST FLOOR PLAN BEFORE ATTIC STAIRS INCLUDED Access Attic floor space shown in blue hatch Existing staircase with landings New staircase with landings Existing staircase with landings New staircase with landings taking up space of twin bedroom and now only useable as single. SECTION FIRST FLOOR PLAN Access Attic floor space shown in blue hatch New staircase required minimum headroom of 2.0m required Existing staircase with landings New staircase with landings Existing staircase with landings New staircase with landings taking up space of bathroom, that now has to be relocated. SECTION FIRST FLOOR PLAN Fire Safety BUILDING REGULATIONS BUILDING REGULATIONS 19972006 Technical Guidance Document B - Fire safety Section B1 :- Means of Escape in Case of Fire :- Sub-section 1.5.3. - provisions that have to be included in cases where the new attic storey floor will be more than 4.5m above ground level (probably a two storey house). It stipulates the folowing requirements :- fire resisting enclosure construction be provided to form protected staircase enclosure - fitting fire resisting doors - automatic smoke detection and alarm system - provision of escape window/doors from the new third storey - layout and configuration of the escape/stairs to comply with the requirements of this section. - separate attic floor by fire resisting construction Fire Safety Escape window to comply with Building Regulations TGD S.1.5.6. Clear opening minimum 0.33 sq.m. and minimum 450mm high Max 1.1m, min 0.6m Max 1.7 m Area beneath window should be clear of obstructions to enable escape and/or rescue. For example : conservatory/back addition. Conclusion Technical Issues which can prove problematic in relation to Attic Conversions: • • • • • Ventilation Structure (roof trusses etc.) Equipment/Services located in the attic Access and its adverse affect on existing living space Fire Safety End of Presentation 26th January 2015