Loft conversion rules: planning, building regulations and party walls

A loft conversion can involve three separate processes: planning, building regulations and the Party Wall etc. Act 1996. Each has its own rules and its own timings. This guide sets out what each one asks of you in England and an order of work that reduces delays.

Planning permission: often not needed, with limits

The Planning Portal says that converting the loft of a house is considered permitted development, so no planning application is needed, if the limits and conditions are met. They come from Schedule 2, Part 1, Class B of the 2015 General Permitted Development Order (Planning Portal, loft conversion). If the limits are not met, or the rights have been removed, a householder or full planning application is required.

The rules do not apply if the house:

• is a flat, or is in a building containing flats
• has already had extra storeys added under permitted development
• was converted from non-residential use, or built, under permitted development rights
• is on designated land: a conservation area, an area of outstanding natural beauty, the Broads, a National Park or a World Heritage Site

For the enlargement itself, the limits are:

• The volume added, including any earlier enlargement, must not exceed the original roof space by more than 40 cubic metres for a terraced house, or 50 cubic metres otherwise.
• It must not go higher than the existing roof, and on the side facing a highway it must not extend beyond the existing roof slope.
• Materials must look similar to the existing house.
• No verandas, balconies or raised platforms, and no new, altered or replaced chimney, flue or soil and vent pipe.
• Side-facing windows must be obscure-glazed and, if they open, sit at least 1.7 metres above the floor of the room.
• The original eaves must be kept. The enlargement must be set back at least 20cm from them so far as practicable, and must not overhang the outer face of the wall.

Hip-to-gable work follows the same volume limits, but the eaves and set-back conditions do not apply to the relevant parts of it (Planning Portal). Other roof alterations, and adding whole storeys, have separate rules. If a design goes over a limit, an architect can tell you whether a small change would bring it back inside permitted development. You can browse loft conversion specialists in the directory, and our guide to what an architect costs explains how their fees work.

Bats and other protected species

Work on a loft or roof may affect bats. The Planning Portal says a survey may be required, and if bats are using the building, a licence may be required (Planning Portal). Ask the question before you finalise the design, because the answer can change the programme.

Building regulations: very likely to apply

Building regulations are separate from planning. For a loft in a house of no more than two storeys, the Planning Portal says they will be applied to make sure of five things:

• the new floor is strong enough
• the structure, including the existing roof, is not endangered
• there is safe escape from fire
• the new stairs are safely designed
• there is reasonable sound insulation from the rooms below

If you make the space liveable, including a spare bedroom you use only now and then, expect a range of alterations. Even boarding out a loft for storage can need approval, because existing joists are often not designed to carry significant weight (Planning Portal).

Fire safety and stairs

Converting a two-storey house usually means fitting new fire-resisting doors, and sometimes partitions, to protect the stairway. The reason given is that it is too dangerous to escape through windows above first-floor level. You also need mains-powered, interlinked smoke alarms in the stairway at each level, and some parts of the structure, such as floors, may need extra fire protection (Planning Portal, fire safety).

A new stair is needed for the new rooms, and retractable ladders or stairs are not normally acceptable. Cutting the opening usually means fitting trimmers around it to carry the load from the cut joists (Planning Portal, stairs).

Full plans or building notice

There are two routes. A full plans application has the authority check and approve the work before it starts. It must decide within five weeks, or two months if you agree (Planning Portal, full plans). A building notice needs no detailed plans, and you can start work two days after submitting it. You do not get the protection of an approved plan, though, and you risk having to correct work that does not comply (Planning Portal, building notice). For a loft with a new stair and structural changes, full plans gets the approval in place before work starts. The detailed drawings are also what a builder needs to price the job.

The loft will usually need drainage and plumbing if it gains a bathroom. The Planning Portal lists drainage, electrics and kitchens and bathrooms among the elements normally needed to meet the regulations in a conversion (Planning Portal). If a shower room is planned, agree where the waste and pipework will run before the structural design is fixed, and find a local plumber to confirm it is workable.

The Party Wall etc. Act 1996

The Act applies in England and Wales. It covers building on or at the boundary of two properties, work to an existing party wall or structure, and excavation near a neighbour's foundations. It is separate from planning permission and building regulations approval (GOV.UK). The explanatory booklet lists cutting into a party wall to take the bearing of a beam, for example for a loft conversion, as work the Act covers. Cutting off projections such as a chimney breast is covered too (GOV.UK, explanatory booklet).

What the booklet says about notices, in short:

• Notice for work to an existing party wall or structure must be served at least two months before the planned start. A notice is valid for a year.
• A neighbour who is content can consent in writing. If they do nothing within 14 days of receiving the notice, a dispute is deemed to have arisen and surveyors resolve it.
• Surveyors make an award, which is final and binding unless a county court modifies it on appeal. Each owner has 14 days from service of the award to appeal.
• Usually the building owner pays the costs of the award, including the adjoining owner's surveyor's fees, where the works are solely for the building owner's benefit.
• There are no set surveyor fees. You negotiate them.

The booklet says an owner considering an appeal against an award may wish to take legal advice, and a neighbour dispute that goes beyond the notices is a property matter. If you need that, you can look for a property solicitor. For the surveyor side of the process, see party wall services in the directory.

A suggested order of work

1. Ask your council whether the house is on designated land or has lost permitted development rights. Check for bats at the same stage; the Planning Portal's protected species page points you to Natural England for advice.
2. Decide whether the design fits permitted development. A Lawful Development Certificate can confirm it; our guide to planning permission for a house extension explains how.
3. Serve party wall notices early. Two months' notice is required for work to an existing party wall, the longest lead time stated in the sources for this list.
4. Submit the building regulations drawings.
5. Get quotes against the same drawings, then start work.