Loft Conversion Building Regulations: Fire Safety and Stairs

What the building regulations cover in a loft conversion

Building regulations approval is required to convert a loft or attic into a liveable space, the Planning Portal says. It names five things the regulations make sure of, from the strength of the new floor to the sound insulation between the conversion and the rooms below.

Planning permission is a separate question: the Planning Portal’s planning guidance says a conversion within the permitted development limits and conditions, such as adding no more than 40 cubic metres of roof space to a terraced house or 50 cubic metres to other houses, needs no planning application. You also need to find out whether the work falls within the Party Wall etc. Act 1996, the Planning Portal says.

Fire regulations for a loft conversion

A typical loft conversion to a two-storey house needs new fire-resisting doors, and sometimes partitions, to protect the stairway, the Planning Portal’s fire safety guidance says. It also needs mains powered, interlinked smoke alarms within the stairway at each level, and it may be necessary to upgrade the fire protection of parts of the structure, such as the floors.

Escaping through windows from floors above first floor level is too dangerous, the Planning Portal says, and a loft room on a two-storey house is above that level. The way out of the new room is down the protected stairway.

Checkatrade’s loft suitability guide advises discussing the fire escape route with your architect or building control at the planning stage, because it can affect the layout of the conversion.

Stair regulations for a loft conversion

A new stair serving the new room will be needed for fire safety, the Planning Portal’s stairs guidance says. Where there is not enough room for a full traditional stair, a space saving stair may be possible, but retractable ladders or stairs are not normally acceptable.

Stair sizes and headroom from Approved Document K

Approved Document K sets the figures below for a private stair, with a reduced headroom figure for loft conversions where 2m will not fit.

Measurement	Approved Document K figure
Rise (the height of each step)	150mm minimum, 220mm maximum
Going (the depth of each step)	220mm minimum, 300mm maximum
Twice the rise plus the going	Between 550mm and 700mm
Pitch	42 degrees maximum
Headroom over flights and landings	2m minimum
Headroom in a loft conversion without space for 2m	1.9m at the centre of the stair, 1.8m at the side

Whether the loft is tall enough for a room at all is a separate check from the stair. Checkatrade looks for 2.2m from the floor to the highest point of the loft, because the new flooring and insulation take up some of that height.

When an alternating tread stair is allowed

Approved Document K allows alternating tread stairs, in one or more straight flights, only in a loft conversion and only when there is not enough space for a stair that meets the normal guidance. Even then the stair can give access to only one habitable room and, if you want them, a bathroom, a WC or both, and that WC must not be the only one in the home.

Floor strength, structure and sound insulation

Three of the five things the regulations make sure of are about the building itself: the new floor must be strong enough, the stability of the structure, including the existing roof, must not be endangered, and sound insulation between the conversion and the rooms below must be reasonable, the Planning Portal says.

Modern trussed roofs, standard after 1965, are more complex and costly to convert because the frame typically needs replacing, Checkatrade says, though a trussed roof does not rule a conversion out.

The stair opening is structural work as well. Where ceiling joists are cut to form it, timber trimmers go around the opening, most likely at least two timbers fixed together, called a double trimmer, the Planning Portal’s stairs guidance says.

Getting approval and the completion certificate

Contact a building control body, usually the local council, to discuss the proposal, the Planning Portal advises. GOV.UK’s guide to applying says you can apply to your local council or to a private registered building control approver, and that with a full plans application, the most thorough option, you can expect a decision within 5 weeks, or 2 months with your consent.

The same application usually brings a completion certificate within 8 weeks of the building work being completed, as long as it complies, GOV.UK says. Without approval you will not have the certificates of compliance you may need when you want to sell your home, GOV.UK’s approval guidance says, so keep the certificate with the paperwork for the house.

Settle who applies for approval, and whether the building regulations costs are in the price, before you agree the job with a loft conversion company. Among the ten loft conversion companies in and around Nottingham that we compare, Lady Bay Loft Conversions takes care of building control certificates, and Roof Rooms supplies full working plans and structural calculations.