Architects for loft conversions

What does an architect do on a loft conversion?

A loft conversion architect is someone on the Architects Register who surveys the roof space, designs the new room and its staircase, and prepares the drawings for building control and, where needed, planning. The job is unusually constrained. The roof, the stair below it and the escape route are all fixed by the existing house, so the design is mostly a matter of fitting the rules into the space.

In practice the architect will measure the roof geometry, test a rear dormer, rooflights or a hip-to-gable change against the planning limits, find a place for a stair that does not wreck the floor below, and coordinate the structural engineer. The Architects Registration Board adds that an architect can obtain quotes from other construction professionals and manage the relationship between you and your builder, if you want that (ARB).

How much roof can you add without planning permission?

Under the General Permitted Development Order, a roof enlargement must not push the volume of the house up by more than 40 cubic metres for a terraced house or 50 cubic metres otherwise. The Order counts any earlier enlargement against that figure (legislation.gov.uk). The enlargement cannot rise above the highest part of the existing roof. Our broader guide to loft conversion rules covers the three consent processes together. This page concentrates on what the design work involves.

What are the rules for dormers?

There is no stand-alone dormer allowance. A dormer is one way to spend the volume allowance above, and it must meet the same conditions on height, the front roof slope and the set-back. In most cases that makes a rear dormer the route with the fewest planning hurdles. A front dormer on a road-facing slope falls outside the permitted development class, as does anything that takes the added volume past the 40 or 50 cubic metre limit.

The architect's contribution is in how the volume is spent. Several modest dormers, a hip-to-gable roof change or a single wide box can all fit the same allowance. They give very different headroom, light and appearance, and they cost different amounts to build. If you are over the limit, the choice is to reduce the volume or apply for planning permission, which costs £548 in England as a householder application (Planning Portal).

Do conservation areas stop a loft conversion?

They do not stop one, but they change the route. The Planning Portal lists not being on article 2(3) designated land as a condition for permitted development, and its definition includes conservation areas and areas of outstanding natural beauty (Planning Portal). In those places a planning application is the normal route, and the council will look at how a dormer or rooflight affects the street. Ask architects whether they have worked with your council's conservation officer. Our page on listed buildings covers the extra consents that apply to those homes.

What do Building Regulations Part B and Part K require in a loft?

Part B covers fire safety and Part K covers stairs. Most loft projects are shaped by them more than by planning. Approved Document B, volume 1, says that where a conversion creates a storey above 4.5 metres, the full escape route should be addressed, with fire-resisting doors (minimum E 20) and partitions (minimum REI 30), upgrading existing doors where needed. In an open-plan layout, new partitions enclose the escape route. Paragraph 2.23 sets out an alternative that includes sprinklers in the open-plan areas (GOV.UK).

The same document says new floors in a loft conversion of a two-storey single-family house should be at least REI 30, with a reduction permitted for integrity and insulation only when one storey is added containing no more than two habitable rooms and not more than 50m² (paragraph 5.4). That is why an architect will ask early how many rooms you want upstairs.

For the stair, the Planning Portal says retractable ladders and stairs are not normally acceptable (Planning Portal). Approved Document K permits an alternating tread stair only in a loft conversion with too little space for an ordinary stair, and only for one habitable room plus, if wanted, a bathroom or WC. It also allows reduced headroom where there is not enough height for the standard figure (GOV.UK). Finding space for the stair is often the single biggest design decision in the whole conversion.

What does the structural engineer do?

The Planning Portal says building control checks that the strength of the new floor is sufficient and that the stability of the structure, including the existing roof, is not endangered. It adds that existing joists will not have been designed to support significant weight (Planning Portal). None of the official pages names who produces the calculations, so treat this as common practice and not a rule: a structural engineer designs the new floor, the steel needed where the roof is opened up, and the support for the stair opening. Ask each architect whether the engineer is in the quote or a separate appointment.

How can you confirm a loft conversion architect is on the ARB register?

1. Ask for the ARB registration number. The Architects Registration Board says every architect has a unique one.
2. Search the Architects Register at arb.org.uk by number, name or registered business address.
3. If the person cannot be found using the details they gave you, ARB says they are not an architect.

ARB also says that using the title in business without being on the Register is a criminal offence (ARB).

What should you ask a loft conversion architect before hiring?

• Have you checked my roof and planning position, and does the design fit within permitted development?
• Where will the stair go, and what does it do to the room below it?
• How will the fire escape route be dealt with, and do I lose a room downstairs to it?
• Is the structural engineer's work in your fee, and who appoints them?
• Will the design need a party wall notice?
• Does your fee cover the building regulations package, and visits during the build?
• How is the fee calculated, and what happens if the design changes? Our guide to architect fees explains the options.
• Can I see lofts you have designed in houses like mine?

To compare practices in your area, browse architects by city or the guides. If the roof work comes with a back extension, see our page on house extensions.