How Long Does a Loft Conversion Take? Build Times by Type

Loft conversion build times by type

Each of the four main types of loft conversion changes a different amount of the roof, so each takes a different time to build. The build times below are from Checkatrade’s timescale guide, and what each build involves is from Checkatrade’s page on the types.

Type	What the build involves	Typical build time
Rooflight or Velux	Windows and ventilators fitted into the existing roofline, with no structural alteration	4 to 6 weeks
Dormer	A box structure with vertical windows that adds headroom and floor space	10 to 12 weeks
Hip-to-gable	The sloping end of a hipped roof extended into a vertical gable wall	10 to 14 weeks
Mansard	Most of one roof slope, typically at the rear, replaced by a near-vertical wall and a flat roof	12 to 16 weeks or more

A dormer, the most popular type, typically takes 10 to 12 weeks, and a hip-to-gable can run to 14 weeks because it involves more structural work than a dormer.

What makes a loft conversion take longer

The type is one of four things that set the build time. Checkatrade names the other three as the condition of the existing loft, its size and the finish, and a fully decorated, furnished room takes longer than a basic shell.

Two build times only compare when both are for the same type, the same rooms and the same finish, so give every company all three when you ask.

The loft conversion timeline before building starts

Up to three stages come before the build, each with its own period: a planning decision if the conversion needs one, the building regulations application, and party wall notice where the work comes under the Party Wall etc. Act 1996.

Stage	When it applies	How long it takes	Source
Planning permission	The conversion falls outside permitted development	Up to 13 weeks for a complex or large project, sometimes under 8 weeks for a simpler one	Planning Portal, Checkatrade
Building regulations, full plans application	Every loft converted into a liveable space	A decision within 5 weeks, or 2 months with your consent	Planning Portal, GOV.UK
Party wall notice	Work such as cutting into a party wall to take a beam	At least 2 months before work on an existing party wall, or 1 month before a new wall at the boundary or excavation	GOV.UK

How long planning permission takes

A conversion within the permitted development limits for a loft needs no planning application, and the Planning Portal says those limits include adding no more than 40 cubic metres of roof space to a terraced house, or 50 cubic metres to other houses.

If yours needs permission, Checkatrade’s timescale guide advises applying before any work starts, and puts a decision at up to 13 weeks for a complex or large project, or often less for a simpler application, sometimes under 8 weeks.

How long building regulations approval takes

The Planning Portal says building regulations approval is required to convert a loft into a liveable space, so every conversion goes through this stage. You apply to your local council or a private registered building control approver, and with a full plans application, the most thorough option, GOV.UK says you can expect a decision within 5 weeks, or 2 months with your consent.

The completion certificate comes after the build, usually within 8 weeks of the work being completed as long as it complies, GOV.UK says.

Party wall notice periods

The Party Wall etc. Act 1996 gives you the right to cut into a party wall to take the bearing of a beam, for example for a loft conversion, but your neighbour has to be given notice first. GOV.UK’s explanatory booklet on the Act sets that notice at least 2 months before work on an existing party wall, or at least 1 month before a new wall at the boundary or excavation.

A notice is only valid for a year, so do not serve it too long before you want to start. If your neighbour has done nothing 14 days after it is served, a dispute is deemed to have arisen, and one agreed surveyor, or a surveyor for each of you, draws up an award.

You wait the full notice period unless your neighbour agrees in writing to an earlier start, and where work begins without notice given in the proper way, the neighbour can seek a court injunction to stop it.

Agreeing a start date with a loft conversion company

Ask each company you are comparing which of these stages it will handle and how many weeks it expects to be on site. Among the Nottingham loft conversion companies ranked on written guarantees and trade memberships, Lady Bay Loft Conversions takes care of design, planning permissions and building control certificates, and says most of its conversions are complete within 8 weeks.

Before a start date goes in the diary, work through each stage your conversion needs.