Most quantity surveyors will give you a generic lump sum for a listed building conversion. A single number, maybe a cost per square metre, maybe a rough estimate based on comparable schemes. At RapidQS, we did it differently for a 7-flat conversion in Frome, Somerset — and the result was a 600-page bill of quantities that gave the contractor, Findlays Construction, genuine pricing confidence before a single nail was driven.
This post breaks down exactly how we priced it, what we found, and what developers and builders need to know before committing to a listed building conversion anywhere in the UK in 2026.
The Project: 1 Palmer Street, Frome BA11 1DS
The scheme at 1 Palmer Street is a listed building conversion in the heart of Frome, Somerset — a market town with a booming property market and strict conservation area controls. The building is being converted by Findlays Construction into 7 residential flats plus a ground floor commercial unit, with a total gross internal area (GIA) of 594.8m².
This isn’t a straightforward loft conversion or a tired terrace house. It’s a multi-storey, multi-unit listed building where every decision — from the type of fixings to the colour of the paint — is subject to approval from the local heritage officer. The planning constraints alone add significant cost and programme risk to a scheme like this.
Our job as quantity surveyors was to produce a bill of quantities accurate enough to tender, detailed enough to manage variations, and honest enough to help the developer understand the true total cost of development — not just the build contract sum.
Why Listed Buildings Cost More: The Heritage Premium
If you’ve never priced a listed building conversion before, the first thing to understand is that the heritage premium is real, significant, and non-negotiable. Here’s what adds cost versus a standard residential conversion:
Heritage Constraints and Conservation Materials
Every material specification has to be compatible with the existing fabric. Lime mortar instead of sand cement. Timber sash windows instead of uPVC. Natural slate instead of concrete tile. Traditional lime plaster instead of modern board and skim. These materials cost more to source and more to install — the trades who work with them are specialists, not generalists.
Listed Building Officer Visits
Heritage officers from the local authority will visit site multiple times during the build. Each visit needs to be managed, paperwork needs to be in order, and any deviations from the agreed specification need to be formally sanctioned. This takes time — and time costs money. We included attendance costs in the preliminaries.
Heritage Protection Prelims
Before you even touch the existing fabric, you need to protect it. Heritage protection boarding on all listed elements, careful soft-strip rather than mechanical strip-out, temporary covers over historic windows and joinery — all of this is in the preliminaries and it adds up fast.
Scaffold Costs
Listed buildings are often in conservation areas, often on narrow streets, often adjacent to other historic buildings. At Palmer Street, the scaffold design had to be approved alongside the building works, and the complexity of accessing a multi-storey listed building in a tight urban setting pushed scaffold costs significantly higher than a standard detached suburban house.
Restricted Working Hours
Planning conditions in conservation areas routinely restrict working hours to protect residential amenity. You can’t just throw unlimited resource at a programme to accelerate it. The site runs to the local authority’s timetable, not the contractor’s.
Our Approach: One Tab Per Flat, Ten Zones Per Tab
The fundamental problem with bulk estimating a multi-unit conversion is that every flat is different. Different floor level. Different orientation. Different existing condition. Different room count. A ground floor flat with a heritage stone fireplace and original cornicing requires completely different work to a second floor flat with a dropped ceiling hiding original timbers.
Our approach at RapidQS: individual tab per flat, ten zones per flat, separate commercial shell-and-core tab.
Ten zones per flat means we priced:
- Zone 1: Demolition and soft strip
- Zone 2: Structural alterations (where required)
- Zone 3: Partitions and linings
- Zone 4: Ceilings
- Zone 5: Mechanical and electrical
- Zone 6: Kitchen fit-out
- Zone 7: Bathroom and en suite
- Zone 8: Flooring
- Zone 9: Decoration
- Zone 10: MVHR ventilation system
This level of detail means the contractor knows exactly where every pound is going. It means variations can be tracked against specific zones. And it means the developer can make informed decisions about specification — if the budget is tight, you can see exactly what you’re cutting and what the impact is.
The Flat-by-Flat Cost Breakdown
Here’s the actual breakdown across the seven flats, based on our bill of quantities:
Flat 1 — Ground Floor, 76.9m² — £46,870
Flat 1 is a ground floor unit at 76.9m², and at £46,870 it’s one of the more expensive flats on a per-m² basis because of the complexity of the existing ground floor condition. The price includes:
- Clear out and soft strip of existing fit-out
- New stud partitions and linings throughout
- Full M&E first and second fix (heating, plumbing, electrical)
- Kitchen allowance: £12,500 (supply and fit, semi-bespoke)
- Bathroom allowance: £7,500 (full suite, tiled, heated towel rail)
- Engineered timber flooring throughout habitable rooms
- Full decoration including heritage-compatible finishes where required
- MVHR unit supply and install
Flat 2 — Ground Floor, 42.7m² — £36,993
Flat 2 is the smallest unit at 42.7m² — a single bathroom, one bedroom configuration. The lower price reflects the smaller footprint and reduced M&E scope, though the per-m² rate is still elevated compared to a straightforward new-build because of the existing fabric constraints.
Flat 3 — First Floor, 81.5m² — £52,433
The largest priced flat at 81.5m², this is a 2-bedroom, 2-bathroom unit on the first floor. At £52,433, the double bathroom adds significant M&E and tile cost, and the first floor location means different structural considerations for partition loadings and floor finish options.
Flats 4–7 — £41,556 to £55,408
The remaining four flats range from £41,556 to £55,408 depending on size, floor level, bathroom count, and specific condition issues identified during our site survey. No two flats were priced identically — because no two flats are identical.
Total flat conversion cost: £465,120
The “Other Costs” That Most QSs Miss
Here’s where a lot of listed building conversion projects go wrong. The contractor quotes you for the fit-out. The developer adds it up. The number looks manageable. Then the project starts and the real costs emerge — costs that were never in the build contract because they’re building-level, not flat-level.
We separated these out explicitly in our QS as “building-level costs” — costs that apply to the scheme as a whole, not to any individual flat:
- Architects and heritage statement: £10,000
- Groundworks: £25,000 — foundation investigations, drainage connections, yard works
- Planning: £10,000 — listed building consent, conservation area application, planning fees
- Fire safety to common areas: £5,000 — fire doors, emergency lighting, alarm systems to stairwells and corridors
- Mains connections: £13,000 — water, gas, and electricity mains upgrades for 7 units (each flat needs its own metered supply)
- Surveys: £5,000 — condition survey, asbestos, structural engineer
- External building refurbishment: £25,000 — pointing, window repairs, roof patch, render to heritage spec
Total building-level costs: £96,500
If you don’t see these costs in your QS, they haven’t been forgotten — they’ve just been left for you to discover mid-project. At RapidQS, we put them front and centre.
Kitchen and Bathroom Allowances: What £12,500 and £7,500 Actually Covers
Developers often ask us to justify the kitchen and bathroom allowances in our QS. Here’s exactly what each allowance covers:
Kitchen — £12,500 per flat
This is a supply-and-fit allowance for a semi-bespoke kitchen including:
- Units, doors, and worktops (mid-range specification, e.g. Howdens Tewkesbury or equivalent)
- Integrated appliances: oven, hob, extractor, dishwasher, fridge-freezer
- Underslung sink with mixer tap
- Tiling to splashback
- Electrical connections (spur outlets, extract fan wiring)
- Plumbing connections for dishwasher and sink
This is not a budget kitchen. For a listed building conversion in Frome targeting the open market, specification matters.
Bathroom — £7,500 per flat
A full suite supply-and-fit allowance including:
- Bath or shower enclosure (shower tray, glass screen, thermostatic shower)
- Back-to-wall WC with concealed cistern
- Vanity unit with basin and mixer tap
- Heated towel rail on dedicated circuit
- Full wall tiling (floor-to-ceiling on wet walls)
- Vinyl or ceramic floor tile
- Extractor fan (connected to MVHR system)
Why MVHR Per Flat is Non-Negotiable
Mechanical Ventilation with Heat Recovery (MVHR) is one of the most commonly debated items in a conversion QS. Developers often try to cut it. We always push back.
Here’s why: Part F of Building Regulations requires whole dwelling ventilation in new residential units. In a listed building conversion, you can’t just open windows and rely on background ventilation — especially if you’re airtightening the envelope for energy performance. MVHR provides the continuous, controlled ventilation that Part F demands, while recovering heat from extract air to reduce energy bills.
Per flat, MVHR adds approximately £2,500–£3,500 to the M&E package. Against a flat conversion budget of £40,000–£55,000, that’s 6–8% of the build cost. Against the Building Control approval risk of not having it, and the tenant comfort problems of inadequate ventilation in a conversion, it’s not negotiable.
The Listed Building Prelims — What a 20-Week Build Actually Costs
Preliminaries on a listed building conversion are a different beast from a standard domestic refurb. Our prelims for the Palmer Street scheme included:
- Project manager at £65/hr for 20 weeks: A dedicated PM is essential for coordinating heritage officer visits, managing subcontractors on a restricted site, and keeping the programme on track. At 40 hours per week, that’s £52,000 in PM time alone.
- Heritage protection boarding: All listed elements, fireplaces, windows, cornicing, and historic joinery protected before works commence. Not cheap, but non-negotiable under the listed building consent conditions.
- Listed building officer attendance: Every significant stage of the works — structural interventions, opening up, M&E installations in listed walls — requires sign-off. We built in officer attendance time explicitly.
- Party wall surveyor: The building shares walls with neighbouring properties. The Party Wall Act 1996 applies. An agreed surveyor needs to be in place before works start on the shared walls.
The Total Development Picture
Here’s the number that matters — the total development spend:
| Flat conversions (7 units) | £465,120 |
| Commercial shell-and-core | £96,500 |
| Building-level preliminaries | £96,500 |
| Total conversion budget | £561,620 |
| Building-level other costs | £96,500 |
| Total development spend | ~£658,000 |
That’s approximately £94,000 per unit across 7 flats in Frome, Somerset.
To put that in context: residential property in Frome is currently selling at £250,000–£350,000 for a 1–2 bedroom flat. At £94,000 build cost per unit plus land, finance, and developer margin, the numbers on a listed building conversion in Frome can work — but only if you know what you’re building before you commit to a purchase price.
This is exactly why an accurate bill of quantities isn’t a luxury on a scheme like this. It’s the difference between a viable development and a financial disaster.
Lessons for Developers and Builders
If you’re looking at a listed building conversion — whether in Frome, Bath, Bristol, or anywhere in Somerset or the South West — here are the key lessons from the Palmer Street scheme:
- Price per flat, not per building. A blended rate misses the variation between units. You’ll overprice the small flats and underprice the complex ones.
- Include building-level costs from day one. Groundworks, mains connections, and external refurbishment aren’t optional — they’re part of the scheme cost.
- Budget for heritage prelims properly. The listed building officer doesn’t work to your programme. You work to theirs.
- Don’t cut MVHR. Part F compliance isn’t discretionary and tenant comfort in a conversion depends on it.
- Get your QS done before you appoint a contractor. A contractor’s estimate without a proper BOQ is a guess. A guess on a listed building conversion is a risk you can’t afford.
Ready to Price Your Listed Building Conversion?
Working on a listed building conversion? Get an accurate QS before you commit to a contractor. At RapidQS, we produce detailed bills of quantities for residential and commercial conversions across the UK — from Somerset to Surrey, from single-unit conversions to multi-flat development schemes.
Get in touch today for a no-obligation conversation about your project. Whether you’re at planning stage or ready to tender, we’ll give you a clear picture of what your conversion will actually cost — not a guess, not a lump sum, but a line-by-line breakdown you can tender with confidence.
📞 Contact RapidQS | 🌐 rapidqs.co.uk