From £30,000 Velux conversion to £85,000 mansard build — add a bedroom, bathroom or office to your London home and add 20%+ to its value. Free site visits, written quote.
A loft conversion in London is one of the highest-ROI investments you can make — often adding 20% or more to the property's value. TrustBuilt Projects manages the entire build end to end: structural calculations, planning advice, dormers, roof works, stairs, plumbing, electrical, plastering, flooring and finishing.
We've delivered every type of loft conversion across London — from simple Velux roof-light conversions to substantial L-shaped dormers and full mansard rebuilds. Every project is quoted in writing after a free site visit.
We visit your property, measure up, listen to your vision, and ask the right questions about what you need.
Written quote after the free site visit.
All work managed end to end by us. Daily progress updates if you want them, clean working practices throughout.
Final walkthrough, snagging, full clean. We leave your property spotless and stand behind every detail.
These are typical London market ranges for 2026 — a realistic guide for budgeting, not a fixed price list. Your exact figure depends on your roof, size and finish, so we give you a fixed written quote after a free site visit.
Ranges include VAT, structural steelwork, staircase, insulation, windows, electrics and standard decoration. Fitted wardrobes, bathroom fit-out and premium flooring are usually extra.
A simple Velux costs far less than a mansard rebuild — your existing roof shape and structure set the starting point.
Bigger rooms, steel beams, chimney removal and reinforced floors all add to the build cost.
Adding a bathroom or en-suite to your new loft means extra plumbing, drainage and waterproofing.
Where the new stairs go — and how tight the access is — affects labour and design time.
Mansards, conservation areas and party-wall agreements add fees and lead time versus permitted development.
Flooring, joinery, lighting, built-in wardrobes and glazing choices move the final figure up or down.
Want an exact figure for your home? Book a free site visit → and we’ll send a fixed written quote.
A typical loft conversion in London ranges from £30,000 for a Velux/roof-light conversion to £85,000+ for a full mansard rebuild. Most dormer conversions land between £45,000 and £65,000 depending on size and finish. We provide a written quote after the free site visit.
Many loft conversions fall under permitted development rights and don't need full planning permission — particularly Velux and rear dormer conversions on detached/semi-detached homes. Mansards, conservation areas and front-facing changes usually do need permission. We'll advise on this at the free site visit.
Most loft conversions take 8 to 14 weeks. A simple Velux conversion can be done in 6–8 weeks. A mansard or L-shaped dormer typically takes 12–16 weeks. We share a timeline with the quote.
Yes, you can stay in the house during a loft conversion. The work happens above your living space, with most access via scaffolding rather than through the house. We protect the staircase and existing rooms, and access is via a separate route until the new stairs go in.
For Victorian and Edwardian terraces (the most common London housing type), an L-shaped dormer usually gives the best space and value — you get the rear dormer plus the L-shape extending over the back addition. Mansards work well on flat-roofed sections.
Yes — a loft en-suite is one of the most popular additions, especially when the loft becomes the master bedroom. We handle all the plumbing, drainage and electrical as part of the build.
If you share walls with neighbours (most London terraces do), yes — the Party Wall Act requires you to serve notice on adjoining owners. We can guide you through this and recommend trusted surveyors if needed.
Combine a loft conversion with a rear or side extension for maximum value add.
Learn more →Add an en-suite to your new loft bedroom — full plumbing and tiling service.
Learn more →We handle all structural work including steels, underpinning, and load calculations.
Learn more →Local loft conversion pages for the areas we work in most: