South East

Budget calculator

What should you set aside?

An honest range before we've met, based on what similar jobs in South East London have cost us to deliver this year. Pick the project, drag the size, choose a level of finish.

1 · Your range

Pick the job, drag the size, choose a level of finish. The figure updates as you go.

Project
Floor area
30 m²
15 m²60 m²
Level of finish
Estimated range · Loft conversion
£75,500 – £97,500
Dormer or Velux conversion with a bedroom and en-suite, staircase, insulation and Building Control sign-off.
—Structural work, staircase and dormer
—Full plumbing and electrics
—Plastering, decoration and flooring

Guide only. Excludes VAT, structural engineer's and planning fees, and anything we find behind the plaster. We'll give you a fixed price after a site visit.

Get this range in writing — book a call
Your figures come with you — we see them before the call.

2 · A real one, costed

What a loft conversion actually cost.

After: A loft that doesn't feel like a loft
Before: A loft that doesn't feel like a loft
⇔
BeforeAfter
Before and after · drag to compareForest Hill · May 2026
Worked example · Loft conversion

A loft that doesn't feel like a loft

£74k
What this one cost
9 weeks
On site
1930s semi
The house

The trick with a loft is to spend the money where you stand, not where you lie down.

Where the money went · £74k
Structure and dormer£31k · 42%
Staircase and joinery£12k · 16%
Plumbing and electrics£10k · 14%
En-suite£11k · 15%
Finishes and decoration£10k · 13%
Read the full project

3 · Whole-project planner

Doing more than one thing?

Loft, extension and kitchen as one programme costs less and finishes sooner than three separate jobs. Tick what you're considering.

Include

Ranges use typical sizes for a South East London terrace and your chosen level of finish above. Fine-tune each job on its own calculator.

Combined estimate · 2 projects
£120,500 – £160,500
Programme14 weeks
One team instead of several≈ £12,000 and 4 weeks
Plan it on a call

4 · Design only

Just want the drawings?

If you already have a builder, Colin's studio can design alone. The fee is credited back against the build if you go ahead with us.

Rooms
3 rooms
1 roomWhole house
Scope
Design fee · Concept + drawings
£2,500 – £4,000
Plans, elevations, lighting and joinery drawings a builder can price from.
—Two design meetings and one round of revisions included
—Drawings issued as PDF and DWG for any builder to price
—Credited in full against a South East Build contract
Book a design consultation

How we price

What moves the number, and what doesn't.

Structure
Steels, foundations and anything that touches the roof move the number most. A knock-through can be a third of a kitchen budget.
Services
Moving a soil stack, a boiler or the consumer unit costs more than people expect. Leaving them where they are is the easiest saving.
Level of finish
Off-the-shelf to made-to-measure roughly doubles the cost of joinery and tiling, but not of the building work behind it.
What we find
Period houses hide things. We carry a 10% contingency in every price and tell you the day we need to touch it.
Access
A terrace with no side access means everything comes through the front door. It adds days, not weeks.
What doesn't move it
Paint colour, handles, taps and lights. Choose freely; these are where taste costs nothing extra.

Further reading

Building costs and VAT: the official sources

A fixed price starts with a twenty-minute call and ends with a survey.
Book the callAsk a question first
WhatsApp a photo of the room — you'll have a rough range by the next working day.
Budget calculator · What should you set aside? · South East Build