A loft conversion is one of the few home improvements where a bad choice is genuinely hard to undo. By the time the tiles are off and the steels are going in, changing builder is expensive and stressful. Most of that risk is decided in the weeks before anyone lifts a hammer.

The checks that separate a solid builder from a risky one aren't complicated. They take a couple of evenings and a willingness to ask slightly awkward questions — ideally before you commit to anything.

1. Understand what their accreditation actually covers

Membership of a trade body means something, but only if you know what you're looking at. TrustMark is the government-endorsed quality scheme for trades, and the Federation of Master Builders runs its own vetting. Competent Person Schemes let registered firms self-certify certain work, usually electrical or heating.

Note the limits. That badge rarely covers the structural and thermal elements of a loft conversion. Your local authority building control team, or a registered approved inspector, still has to sign off the work. So ask directly: who is arranging Building Regulations approval, and what will they inspect?

Then verify. Take the membership number, check it on the scheme's own website, and confirm it covers loft work rather than windows. A logo on a van proves nothing.

2. Ask for insurance certificates — and read them

Three policies matter: public liability, employer's liability (a legal requirement if they employ anyone, including casual labour), and contract works or all-risks cover for the project itself. Ask for the certificates as PDFs, not a photo of a folder.

Check they name the same company you're contracting with, that the dates still cover your build, and that subcontractors are included — most lofts involve a roofer, an electrician and sometimes a steel erector. If something doesn't add up, ask your own home insurer what would happen if the loft leaked and the builder's policy didn't respond.

3. Talk to references, then visit a job

Two glowing references on the builder's own letterhead are worth very little. Ask for three customers with lofts like yours — similar roof shape, similar dormer or rooflight — finished in the last year or two. Then phone them and ask:

  • Did the work finish close to the date you were given, and if not, why?
  • How were changes and extras priced and agreed?
  • What went wrong, and how quickly was it sorted?
  • Would you use them again?

If a customer is happy for you to look, visit a finished loft and head for the awkward places: the junction between old and new ceiling, headroom at the top of the stairs, the plastering around rooflights, the roof finish. A tidy site mid-build tells you plenty too.

4. Insist on a written, itemised quote

An estimate is a guess in writing; a quote is a price. If you want the latter, ask for the words "fixed price" and check whether it still holds if the design changes.

A useful quote is itemised enough to show what you're paying for: scaffolding, structural steel and its installation, the structural engineer's calculations, building control fees, party wall costs, skips, electrics, plumbing, plastering, insulation, stairs and VAT.

Exclusions matter just as much. Ask specifically about decoration, floor finishes, a shower room, moving a boiler or water tank, asbestos in older homes, and strengthening existing floor joists. Get the answers in writing and attach them to the quote. Anything left unwritten becomes a conversation later, usually an unpleasant one.

5. Agree a payment schedule built around milestones

A large deposit before work starts is a warning sign, and so is a request to pay in cash. A sensible schedule is tied to stages you can see: scaffold up and roof stripped, steels in, weathertight, first fix complete, plastered, snagged.

Pay against invoices that match the contract, by bank transfer, and keep records. Consider holding back a retention — a small percentage released a set period after completion, once you've lived through some heavy rain and used the stairs properly. Builders sometimes resist, but it's a normal arrangement and worth negotiating.

Read the payment terms against the programme. If most of the money is due three-quarters of the way through, you'll have very little leverage at the end. On a large project, it's worth having a professional review the contract before you sign it.

6. Pin down the structural, legal and aftercare side

Loft conversions are structural work. Confirm in writing who appoints the structural engineer, who submits and pays for Building Regulations approval, and who handles party wall matters if you share a wall with a neighbour. Party wall law is a legal area — if a dispute looks likely, take proper advice rather than relying on your builder's view.

Ask which contract will be used: a recognised form such as JCT Minor Works, with a schedule of works and start and finish dates, is a reasonable starting point. Confirm working hours, access, where materials are stored and who protects floors and furniture. Then get the guarantee in writing: what it covers, how long it lasts, whether it's insurance-backed, and what happens if the firm stops trading.

Your pre-signature checklist

Run through this the evening before you sign. If you can't tick every line, you're not quite ready.

  1. Accreditation verified on the scheme's own website, not just shown on paperwork.
  2. Public liability, employer's liability and contract works certificates checked and in date.
  3. Three recent, similar references phoned — and one loft visited in person.
  4. Fixed-price quote in writing, itemised, with exclusions listed.
  5. Payment stages tied to milestones, with a retention held back.
  6. Written contract with start and finish dates and agreed working hours.
  7. Building control, structural engineer and party wall responsibilities confirmed.
  8. Guarantee length and cover in writing.
  9. Company checked on Companies House and contactable at a fixed address, not just a mobile number.
  10. Snagging process agreed: who lists defects, and how long they have to fix them.

None of this is unreasonable to ask. A builder worth hiring will answer without flinching and put it in writing, because they want the job to run smoothly too. The ones who get defensive are telling you something useful.

Photo: jarmoluk / Pixabay