Converting an existing loft space can be a cost effective way of increasing living accommodation. Alan Holmes Building Surveying Services can carry out a feasibility study and fully design and project manage a loft conversion to your home. Below are just some of the things you have to consider.

Is planning permission needed for loft conversions?

Planning permission is not normally required. However, permission is required where you extend or alter the roof space and it exceeds specified limits and conditions. A loft conversion for your house is considered to be permitted development, not requiring an application for planning permission, providing the house is not listed, subject to the following limits and conditions:

• A volume allowance of 40 cubic metres additional roof space for terraced houses;
• A volume allowance of 50 cubic metres additional roof space for detached and semi-detached houses;
• No extension beyond the plane of the existing roof slope of the principal elevation that fronts the highway – in other words no dormers on the front elevation facing the highway;
• No extension to be higher than the highest part of the roof;
• Materials to be similar in appearance to the existing house;
• No verandas, balconies or raised platforms;
• Side-facing windows to be obscure-glazed; any opening to be 1.7m above the floor;
• Roof extensions not to be permitted development in designated areas, such conservation areas;
• Roof extensions, apart from hip to gable ones, to be set back, as far as practicable, at least 20cm from the original eaves;
• The roof enlargement cannot overhang the outer face of the wall of the original house.

How can I know whether my loft is suitable for a loft conversion?

Before commencing a loft conversion it is important to assess the feasibility of the project. This will involve inspection of the existing loft & dwelling to assess the roof structure & shape.

The overall form, construction and profile of the roof will have a major bearing on the whether the roof is suitable for conversion to a usable space. Traditional cut timber pitched roofs with gable ends walls (cavity walls or solid walls at least 250mm thick) and horizontal ridges are generally easier to convert and can normally support structural beams. Hipped roofs or roofs with intersecting pitches and valleys may require more complicated structural designs.

Trussed rafter roofs constructed using a series of complex trusses should only be altered, modified and converted in compliance with details and calculations carried out by a suitable qualified and experience structural engineer. No trussed rafter should ever be cut or modified in any way until a new supporting structure is in place.

Existing lintels and wall structure that will support the new storey loads from the proposed works need to be inspected to ensure that they are adequate and suitable. All existing timbers should be in a sound condition, any defective timber is to be replaced with new in compliance with details and calculations carried out by a suitable engineer. An asbestos survey may be required before works commence.

Head room available

Head room available- Is measured vertically from the top of the new floor (which typically can be 200mm above the existing ceiling joists) to the underside of the new horizontal/sloping ceilings (which can typically down stand 50 -75mm from the existing roof structure). A minimum headroom of 2.0m is required at the head of the stairs to comply with building regulations. A ceiling height of 2.2 to 2.3 is preferred in the centre of the roof in habitable rooms reducing to 0.800 to 1.2m for the side walls on sloping ceilings so low furniture can be placed in front of them. If your existing roof pitch is less than 30 degrees and roof span is less than 6 metres, a loft conversion may be impractical and the only possibility may be to remove the roof completely and replace it.

Means of escape

Means of escape- Three storey houses will require a protected stairs direct to a final exit at ground floor level or give access to at least two escape routes to final exits at ground level which will require separated by fire resisting construction and fire doors. Alternatively, the new top storey can be separated by fire resisting construction and provided with an alternative escape route, or a domestic sprinkler system can designed by a fire engineer.

Roof ventilation

Roof ventilation to be continuous with the wall insulation but stopped back at eaves or at junctions with rafters to allow a 50mm air gap. Cross ventilation to be provided by a proprietary eaves ventilation strip equivalent to a 25mm continuous gap at eaves level with insect grill. Ventilation to the roof space may be provided by using a proprietary BBA or similar approved breathable roof membrane is used. Flat roof insulation is to be continuous with the wall insulation but stopped back to allow a continuous 50mm air gap above the insulation in ventilated cold decks. Cross ventilation to be provided on opposing sides by a proprietary eaves ventilation strip equivalent to a 25mm continuous gap at eaves level with insect grill. Note: Warm roof applications ie insulation above the structural deck do not require ventilation.

existing external walls

Upgrading existing external walls Where existing external walls are to be used as part of the loft conversion and have a threshold U-value worse than 0.7, the U-values should be upgraded to 0.55 for cavity walls & 0.3 for solid walls. Existing solid external walls less than 328mm thick in rendered stone or brick or less than 250mm thick in rendered blockwork, should be tanked internally with a BBA or other approved tanking system to prevent the ingress of moisture into the building.

sound insulation

Upgrading sound insulation of existing separating walls Existing wall should be at least 100mm thick, of masonry construction and plastered on both faces. With other types of existing wall the independent panels should be built on both sides.

Intermediate upper floor(s) Floor

Intermediate upper floor(s) Floor to be constructed of kiln dried structural grade timber joists with sizes and spacing suitable for the proposed clear span. Floor void between joists to be insulated with a minimum thickness of 100 mm of 10Kg/m³ proprietary insulation quilt, to give overall 30 minutes fire resistance.

Internal stairs

Internal stairs Stairs to be constructed in materials to Clients choice to BS 5395 & BS 585 as detailed below:- (Spiral & helical stairs to be designed to BS 5395: Part 2) Stair pitch not to exceed 42° and design to be based upon dimensions taken from site and drawing.

Stair to have a minimum headroom of 2000mm above stair pitch line and to be provided with landings clear of any door swing top and bottom equal in length to the width of the stairs. If doors open across a bottom of a landing- a clear 400mm space must be maintained across the width of the flight. There is no minimum stair width for new extensions or replacement stairs in existing dwellings. Handrails must be provided on one side of the stairs, at a height 900-1000mm above floor/nosing levels and continuous throughout their length. All guarding is to be at a minimum height 900mm above floor/nosing levels and continuous throughout their length, with non climbable vertical balustrading, no gaps to exceeding 100mm and all constructed to resist a horizontal force of 0.36kn/m. All open treads, gaps etc should not exceed 100mm.

 

Loft Conversion for single storey buildings

conversion of Bungalows or similar single storey building to form a new first floor do not require a protected hall, landing or fire doors, but the supporting floor must still be provided with 30 minute fire resisting construction. The stair may be positioned in a ground floor room such as living room, provided there is an external door that opens directly to the outside for means of escape. All rooms or bedrooms on the first floor (except bathrooms or toilets) must be directly accessible off the stair landing. Smoke detection must be installed as detailed below, with an additional interlinked heat detector at ceiling level in kitchens which are open to the stairs at ground level. Means of escape windows to be fitted with proprietary hinges to open to the minimum required clear width of 450mm. Direct access to a protected stairs must be maintained.

Protected stairway

Protected stairway The new and existing stairs, landings and hallway from the new 3rd storey down to the ground floor must be protected and enclosed in 30-minute fire resisting construction and the protected stairs must discharge directly to an external door. 30 minutes fire resisting construction is required to the underside of the new upper storey floor.

Residential sprinkler systems

Residential sprinkler systems for means of escape Where fire safety requirements of the building regulations cannot be met for loft conversions, proposals for fire engineered solutions may be allowed against the requirements of Approved Document B where a risk assessment has been carried out by a suitably qualified and experienced fire engineer and approved by building control before works commence on site.

Fire doors

Fire doors All rooms onto the protected stairs (except bathrooms or toilets providing the enclosing walls have 30 minutes fire resistance) are to be provided with FD20 (or FD30) fire doors to BS 476- 22:1987 fitted with intumescent strips rebated around sides & top of door or frame with intumescent strips. Any glazing within the fire door or stairway enclosure is to have 30 minutes fire resistance including the beading as detailed in above options. Existing solid/hardwood doors may achieve the required 20 minutes fire resistance or can be upgraded with proprietary intumescent products applied as manufacturers details to achieve 20 minutes fire resistance.

Smoke alarms

Smoke alarms All floors to be provided with mains operated interconnected fire detection and fire alarm system to BS 5446 & installed in accordance with the relevant recommendations of BS 5839 – 6: 2004 to at least a Grade D Category LD3 standard.

Fire resistance to new storey

Fire resistance to new storey floor The new 3rd storey floor storey should be separated from the remainder of the house by 30 minute fire resisting construction e.g. a minimum of 12.5 mm (if existing or 15mm if renewed) plasterboard and skim to ceilings and sides of stud walls and provided with a 20 minute fire door with intumescent strips at either the bottom or top of the new stair leading to the loft conversion. Where there is an openings within 1.0m of a boundary, an unprotected opening of 1m2 (e.g. window) is permitted every 4.0m on the same building face.

Ventilation

Ventilation to be provided to all habitable rooms equal to 1/20th (5%) floor area where the external windows/doors. The area of external windows, roof windows & doors should not exceed 25% of the usable internal floor area otherwise SAP calculations may be required (these can be provided by AHBSS). Means of escape windows to be fitted with proprietary hinges to open to the minimum required clear width of 450mm. Escape windows are not required where protected routes are provided in compliance with this guidance. Mechanical extract ventilation & fresh air inlet are required for habitable rooms without natural ventilation which must designed by a ventilation specialist having a minimum of 4 air changes per hour. Background ventilation to be provided equivalent to 8000mm² to habitable rooms and 2500mm2 to wet rooms via hit and miss or 2 stage catches fitted to windows.

Foul water drainage

Foul water drainage All W/Cs to have trapped outlet connected to 100mm diameter pipes, and to be provided, with a wash hand basin with hot and cold running water. Sanitary appliances such as wash hand basin, baths, showers, sinks etc, to be provided with 50mm diameter waste pipes laid to falls and 75mm deep seal traps. Where waste pipe runs exceed 4m BBA approved air admittance valves are to be fitted above appliance spill over level.

Electrical Installations

Electrical Installations New or works to existing electrical circuits or systems must be designed, installed, tested and certified to BS 7671 or with the current editions of the IEE regulations by a competent person in compliance with Approved Document P of the Building Regulations. All switches and sockets including the consumer unit, ventilation & service controls etc, should be fixed between 450-1200mm above floor level. Accessible consumer units should be fitted with a child proof cover or installed in a lockable cupboard.