Worthing Loft Conversions

How Long Does a Loft Conversion Take?

Loft conversion build time typically ranges from 4–6 weeks for a Velux conversion to 12–16 weeks for a mansard, depending on conversion type. That excludes design, survey and any planning permission time beforehand, which can add several weeks to months on top.

How long does each conversion type take to build?

Build time scales with how much the roof structure changes — Velux conversions are fastest since the roofline stays the same, while mansards take longest because most of the rear roof is rebuilt.

The build programme is driven mainly by how much the roof's external shape and structure change. A Velux or rooflight conversion, which alters no external structure, is the fastest at roughly 4–6 weeks. A standard rear dormer, involving a new structural box on the roof, typically takes 8–10 weeks. Hip-to-gable and L-shaped dormer conversions, which rebuild more of the roof or add a second dormer, generally run 10–14 weeks. A mansard, effectively a partial rebuild of the rear roof, is the longest at 12–16 weeks.

What happens before the build even starts?

Survey, design and (where needed) a planning application all happen before construction begins, and can add anywhere from a few weeks to several months depending on the route.

Before any building work starts, a survey confirms what's structurally achievable, followed by a design phase to finalise the layout, staircase position and specification. Where the project qualifies as permitted development, this pre-build phase can be relatively short. Where a full planning application is needed — common for mansards, and possible for other types depending on location and property history — the application and decision process typically adds several weeks to a few months before Building Regulations approval and construction can proceed.

What can extend a loft conversion's build time?

Party wall negotiations, weather delays affecting roof-open stages, and trade availability are the most common causes of a project running longer than its baseline programme.

Party wall matters can add time if a neighbour appoints a separate surveyor or raises concerns that need resolving before work starts on a shared wall. Weather is a genuine factor during the roof-open stage of any conversion, since that period is the most weather-sensitive part of the whole build. Trade and material availability can also shift a programme, particularly for bespoke items like a specific staircase design or roofing material. A realistic project-specific programme, including contingency, is confirmed at survey stage rather than assumed from these general ranges.

Typical build time by loft conversion type

Typical build time by loft conversion type
conversion type	typical build time
Velux / rooflight	4–6 weeks
Standard rear dormer	8–10 weeks
L-shaped dormer	10–14 weeks
Hip-to-gable	10–14 weeks
Bungalow (trussed roof)	12–16 weeks
Mansard	12–16 weeks

Related conversion guides

Velux loft conversions in Worthing dormer loft conversions in Worthing mansard loft conversions in Worthing

Frequently asked questions

Does build time include the design and planning stage?

No — the ranges here cover construction only. Design, survey and any planning application time happen beforehand and should be added on top.

Can I still live in the house during a loft conversion?

Most homeowners do stay in the house throughout, though noise and access disruption are highest during the roof-open and structural stages.

Why do hip-to-gable conversions take as long as L-shaped dormers?

Both involve a larger scope of structural roof work than a single standard dormer, which is the main driver of build time rather than the specific technique used.

What's the fastest loft conversion I can get?

A Velux or rooflight conversion is typically the fastest, at around 4–6 weeks, since it doesn't alter the roof's external structure.