How House Extension Expert works
Two things happen here: you work out what you are allowed to build and what it should cost, and — only if you want to — you get put in front of people who can build it.
1. Work out whether you are allowed to build it
Most extensions in England are decided by one of two routes: permitted development, which needs no planning application if you stay inside specific limits, or a full planning application. The limits depend on the property type, whether it is a rear or side extension, how many storeys, and whether the property sits on designated land. Our planning pages set out the actual limits with the Planning Portal and GOV.UK sources next to them.
Either way, Building Regulations almost always apply. Permitted development is not an exemption from Building Control — a point that catches a lot of people out.
2. Work out what it should cost
Our cost pages give indicative 2026 ranges by extension type, storeys and region, plus the decisions that move the number more than floor area does — ground conditions, steelwork, glazing, drainage. The figures come from BestBuilders’ 2026 regional cost model (published national cost guides × a regional labour index, averaged across 519 UK towns). They are a sanity check against the quotes you receive, not a substitute for them.
3. Get quotes, if and when you want them
When you are ready, the quote form asks nine questions about the job and then your postcode. We pass your enquiry to our lead partner, Bark, which runs the network of tradespeople; specialists who cover your area contact you directly. Typically that is a handful of them, usually within a day or two.
You are not matched to anyone by us, and nothing is booked on your behalf. Any quote, contract, price and guarantee is between you and the builder you choose — and you are free to choose none of them.
What we do not do
- We do not vet, accredit or inspect the specialists who contact you, and we do not verify their insurance, qualifications or trade-body membership. Ask for proof of public liability insurance and recent references, and check them yourself before work starts.
- We do not sell your details to a list. They go to our lead partner for the purpose of getting you quotes, as set out in the privacy notice.
- We do not charge you anything, at any point. We are paid by the partner — see how we get paid.