A beautiful set of drawings is only as good as the team that builds them. On a high-end extension, the main contractor decides whether you get the finish you were promised, on the date you were promised, for the price you agreed.
Most extension horror stories don’t start with bad luck. They start with the wrong builder: vague quotes, no proper contract, nobody running the site, and costs that creep week after week.
If you’re planning an extension, basement or major renovation in London, Bromley, Bexleyheath, Canterbury or anywhere in the South East, these are the questions worth asking every builder on your shortlist before you sign anything.
10 questions to ask any extension builder
1. Will we sign a proper building contract?
A serious contractor will put the job on a recognised contract, such as a JCT Minor Works or JCT Homeowner contract. It sets out the price, the programme, how changes are handled and what happens if things go wrong. If the answer is “we’ll just go off the quote”, keep looking.
2. Is the price fixed, and what’s excluded?
Ask for a fully itemised quote, not a single figure. Check what’s included (skips, scaffolding, structural steel, making good, decoration) and which items are provisional sums. The fewer surprises on paper, the fewer on site.
3. How are changes (variations) priced and agreed?
Changes happen on almost every job. The right answer is that every variation is priced and agreed in writing before the work is done, so you always know where the budget stands.
4. Who will actually be on site every day?
Some builders win the job, then leave it to a rotating cast of subcontractors. Ask who runs the site day to day, who your single point of contact is, and how often you’ll get progress updates.
5. What insurance do you carry?
Ask to see public liability and contractor’s all-risks cover, and employer’s liability if they have staff. Check the certificates are current and the cover is suitable for the value of your project.
6. Can I see similar projects and speak to past clients?
Look for work of a similar size and spec to yours, ideally nearby. A good builder will happily put you in touch with previous clients and, where possible, show you a finished job in person.
7. What does the programme look like?
Ask for a written programme showing the key stages and a realistic completion date. Find out how delays are communicated and what allowance has been made for weather and lead times on materials.
8. How are payments structured?
Payments should follow progress, either at agreed stages or by monthly valuation of work done. Be wary of large upfront deposits. Ask whether a retention will be held back until any snagging is complete.
9. Who handles building control, party walls and sign-off?
Check who deals with building control inspections, any Party Wall Act notices with neighbours, and the final completion certificate. You’ll need that certificate when you sell, so make sure it’s part of the handover.
10. What happens at handover?
Ask what you’ll receive at the end: certificates, guarantees, warranties for installed products and an operation and maintenance pack. Ask how snagging is handled and how long the builder stands behind the work.
Red flags to walk away from
- A quote that’s far cheaper than the others with no clear reason why
- Pressure to start quickly or pay a big deposit in cash
- No written contract, or reluctance to use a standard one
- Can’t or won’t show insurance certificates
- No address, no landline, no past clients you can speak to
- Vague answers on who will run the site
- “We don’t need building control for that” without checking
How we work at Ryan and Sons
We’re a family-run main contractor delivering high-end extensions, basement and loft conversions, refurbishments and new builds across London and the South East. Every project gets complete cost transparency, a realistic programme and a member of our team on site from start to finish.
We work on proper contracts, price every variation before it happens, and hand over a full certificate and maintenance pack at the end. Quality, integrity and client focus aren’t slogans for us; they’re how we keep winning work through recommendation.
Planning an extension in Bromley, Bexleyheath, Canterbury or London? Get in touch to book a site visit and talk through your project.
