There’s a certain type of project that separates the builders who price properly from the ones who wing it on a back-of-envelope calculation.
A listed building conversion is one of them.
This month, we worked with a regional contractor on exactly that — an existing listed building in a Somerset market town, being converted into 7 residential flats and a ground floor commercial unit. Total gross internal area: 594.8m². Total priced: £434,803 ex VAT. Including VAT: just over £521,000.
Here’s how we approached it, what we found, and why getting the pricing right on a job like this matters more than almost anything else.
The Brief
The client — an experienced regional contractor — came to us with architectural drawings for a full change-of-use conversion. The existing building was a listed property, which immediately changes the complexity of the whole job.
You’re not just fitting out a blank shell. You’re working inside a protected historic building where every material choice, every fixing, every structural intervention has to be sympathetic to the original fabric and is subject to listed building consent conditions. That means slower working, more careful sequencing, higher-spec materials in certain areas, and a whole additional layer of statutory compliance.
The brief: produce a flat-by-flat pricing breakdown covering all building works, plus a commercial unit on the ground floor for a future tenant. M&E, kitchens, bathrooms, and structural works were flagged as Provisional Sums — because without a confirmed M&E specification or structural engineer’s design, you’re guessing. And on a listed building, guessing is expensive.
The Project Breakdown
Seven flats ranging from 42.7m² to 91.8m², spread across ground, first, second, and third floors. Each flat priced individually — because that’s how a builder actually has to think about the job.
- Flat 1 — Ground floor, 76.9m² — £46,870
- Flat 2 — Ground floor, 42.7m² — £36,993
- Flat 3 — First floor, 81.5m² — £52,433
- Flat 4 — Second floor, 58.5m² — £41,556
- Flat 5 — Second floor, 87.5m² — £54,166
- Flat 6 — Second floor, 73.1m² — £45,773
- Flat 7 — Second/third floor, 91.8m² — £55,408
- Commercial unit — Ground floor, 82.8m² shell & core — £17,699
Preliminaries (covering the whole project): £83,904
That prelims figure is worth talking about, because it’s the number that gets cut first when a builder is trying to sharpen a bid — and it’s almost always a mistake.
Why the Prelims Were £83,904
On a standard domestic extension, you might see prelims at £8,000–£15,000. On a project like this, it’s a different conversation entirely.
A 20-week programme with a full-time site manager at £65/hr adds up quickly — that’s £52,000 on its own. But there’s more to it.
Listed buildings require heritage protection throughout the works. You’re not just boarding up the floor and cracking on. You’re protecting original stonework, historic window reveals, period joinery. That means additional labour, bespoke dust and damage screens, and a much more careful approach to site logistics.
Then there’s the statutory layer: building control fees, party wall surveyor, listed building officer inspections, CDM duties as principal contractor. These are all Provisional Allowances — they might go over or under — but they need to be in the price. Missing them entirely is how contractors end up arguing with clients over costs that were always going to happen.
The scaffold for a multi-storey town centre building on a restricted street, including hoarding licence from the council, was provisionally allowed at £9,500. Some contractors leave scaffold out entirely because it’s “provisional.” That’s not the same as including it properly and flagging it clearly.
The Listed Building Complication
Every structural opening in a listed building requires a structural engineer’s design and listed building consent. The structural zone in every flat was priced as a Provisional Sum — £2,500 per flat — with a clear note that SE confirmation is required before the price is firmed up.
This is honest pricing. It tells the client: here is what we know, here is what needs confirmation, here is what we’ve allowed, here is the risk.
The acoustic specification was also more complex than a standard conversion. With seven flats above one another, Part E compliance for sound insulation between separating floors and walls is a Building Regulations requirement — not a nice-to-have. Rockwool RW5 acoustic insulation between all separating elements was priced throughout.
How We Priced Each Flat
Each flat followed the same eight-zone structure:
- Zone A — Demolition and soft strip
- Zone B — Structural works and new partitions
- Zone C — First fix preparation (floor boarding, screed, backer board)
- Zone D — Plumbing, heating and drainage (Provisional Sums)
- Zone E — Electrical installation (Provisional Sums)
- Zone F — Plastering and internal linings
- Zone G — Flooring finishes (PC Sums)
- Zone H — Kitchen and second fix carpentry
Every material component was separated from every labour component. Every line item had a quantity, unit, rate and total. Nothing lumped together. Nothing hidden in a round number.
That matters because when the contractor goes to tender or negotiates with sub-contractors, they need to break the job down. If you’ve handed them a single line saying “Flat 3 — £52,000,” they can’t do anything useful with it. If you’ve handed them 80 line items with quantities and rates, they can challenge every one, get competitive quotes, and understand exactly what they’re buying.
The Commercial Unit
The ground floor commercial unit — 82.8m² — was priced as shell and core only. Strip back, plaster, screed, provide a basic M&E distribution board and sanitary provision for a future tenant.
The fit-out was deliberately excluded. Different tenants need different things — a coffee shop has different requirements to a professional office. Shell and core gives the developer a clean number for the structural work, with fit-out costed separately once a tenant is confirmed.
The commercial unit came in at £17,699 ex VAT — £214/m² for shell and core in a listed building in the South West. Realistic. Not cheap, but honest.
The Overall Cost Per Square Metre
The total project came to £731/m² on gross internal area, excluding VAT.
For context, our SW England benchmark for a listed building conversion is £1,400–£2,200/m² for the full scope including M&E, kitchens and bathrooms to finished standard. This price covered structural, fabric and plaster works only — M&E and fit-out remain as Provisional Sums pending specification confirmation. The two figures aren’t directly comparable, but knowing both helps a client understand their budget properly.
Three Things This Type of Project Always Teaches Us
1. The prelims are almost always higher than people expect. A listed building in a town centre with a 20-week programme and statutory obligations is not a domestic extension. The site management alone is a significant cost. Don’t be surprised by a prelims figure that looks large — be more suspicious of one that looks too small.
2. Provisional Sums are your friend. Used properly, they don’t make a price look weak — they make it honest. A contractor who has clearly thought through what’s confirmed and what needs further information is easier to work with than one who has buried uncertainties in inflated round numbers.
3. Flat-by-flat pricing is essential on a multi-unit scheme. The contractor needs to understand each unit individually — for sub-contractor negotiations, phasing decisions, and cash flow planning. A single lump sum for “all flats” is not a pricing document. It’s a guess wearing a spreadsheet’s clothes.
Working with RapidQS UK
This project was turned around within 48 hours of receiving the drawings. 10 tabs, over 600 priced line items — 7 individual flat tabs, a commercial unit tab, full preliminaries, and a trade summary.
If you’re a contractor or developer working on a conversion, a listed building project, or a multi-unit scheme and you need accurate pricing without the wait — that’s what we do.
Send us your drawings. We’ll have a detailed estimate back to you within 48 hours.
