How we chose
We began with the extension builders serving Telford. Scheme memberships were sourced from the Federation of Master Builders and TrustMark registers and each firm's own website [1] [2]. Every business first had to meet our basic checks: it is who it says it is, it is trading today and can be reached, and anything it must hold by law is in place. A dozen firms met all three and ten are ranked. What customers say counts most toward the score, qualifications count next, then trading history, stated cover, pricing clarity and website detail. All evidence is dated September 2026.
How to hire
Start by matching the professional to the job. An extension builder owns the foundations, walls, roof and knock-through; a design practice such as LMDS Architectural produces the drawings and steers the planning submission; a kit supplier such as Timber Kit Solutions designs and cuts the timber frame your own builder then raises. Most extensions also need a structural engineer for the steels and foundations, whatever route you take. Decide which of these you need first, and ask each firm what it does in house.
Then settle the planning question. Many single-storey rear extensions count as permitted development and need no application, within strict limits on height, width and how far they project behind the original house [5]. Larger rear extensions can go further under a neighbour consultation scheme with prior approval from the council, but flats, converted houses and streets with an Article 4 direction are excluded, so never assume [5]. Telford & Wrekin Council takes applications through the Planning Portal, so check its pages and, where the answer is borderline, apply for a lawful development certificate before you build [6].
Planning permission is only half the paperwork: almost every extension also needs building regulations approval, even where no planning application is needed [4]. In Telford you apply through the council's building control team, either with full plans checked before work starts or, for straightforward jobs, a building notice two days before work begins [7]. Surveyors inspect the work at key stages, and the completion certificate at the end matters when you sell or remortgage, so arrange the final inspection and hold the last payment until the certificate is in your hands [7].
If your house shares a wall or sits close to a neighbour, the Party Wall Act applies on top of both regimes. For a semi or terrace with a shared wall, or foundations dug near a neighbour's building, you must give written notice describing the work, generally two months ahead for work to the shared structure and one month for new walls on the boundary or nearby excavation, with any agreement in writing [3]. Talk to the neighbours first with drawings in hand, since an early conversation beats a formal dispute with surveyors later. The party wall agreement is separate from planning permission and building control, and you need all three where all three apply [3].
Check credentials before you book. Extension building has no mandatory registration scheme, so treat memberships as evidence rather than licences: search the Federation of Master Builders or TrustMark registers for the business name and confirm the entry matches the firm on your quote [1] [2]. Ask for public liability insurance details in figures and in writing, plus recent local jobs you could view, and read the reviews on each source rather than the headline score alone. Citizens Advice publishes plain-English guidance on hiring traders and template letters if things go wrong, worth reading before you sign [9].
Get three itemised written quotes on the same written scope so you compare like with like, as TrustMark recommends [2]. Each quote should separate labour, materials and VAT, name what is included down to steels, glazing and making-good, and set dates, hours, access, waste removal and payment stages. A deposit for materials is normal; full payment before completion is not. Use a written contract covering all of it, and agree any change to the scope in writing with its price before the work happens [2] [9].
At the end, collect the paperwork before you pay the balance: the building control completion certificate, structural calculations, guarantees for glazing and roofing, and every invoice marked paid [7]. Photograph each stage so hidden items such as foundations, steels and insulation are on record. File everything with the house papers, since buyers and lenders will ask for the completion certificate and the guarantees when you sell or remortgage [7].
Pricing
As of summer 2026, a builder-written national cost guide puts a standard single-storey shell at £1,500 to £2,000 per square metre, rising to £2,000 to £2,800 for a good specification with bifold doors, a rooflight and underfloor heating, and £2,800 to £4,000 for a high-specification glazed design [8]. On that basis a typical twenty-square-metre rear extension at mid specification costs £40,000 to £56,000 for the shell before VAT [8]. London and the South East add a fifth or more to every band, so Telford jobs usually land below those headline pressures [8].
Glazing moves the price most: bifold or sliding doors and rooflights add thousands against standard windows, and a fully glazed wall lifts the whole project a band [8]. The roof build-up, the steel for the knock-through into the existing house, and ground conditions under the foundations each swing the total by thousands more, while a kitchen fit-out on top of the shell adds roughly £10,000 to £25,000 for units, worktops, appliances and plumbing [8].
Those per-metre rates exclude VAT, professional fees and fit-out, so budget beyond the shell [8]. Expect drawings and any planning submission around £1,500 to £3,500, structural engineering around £600 to £1,200, and the building control application around £500 to £1,200, plus a contingency of a tenth or so for what the ground or the existing walls reveal [8]. Ask whether each quote includes VAT and at what rate, since the construction VAT rules carry exceptions and the wrong assumption is expensive [10].
Get the scope in writing before work starts: exactly which foundations, walls, roof, glazing, electrics, plumbing and finishes are included, how waste is removed, which certificates you will receive, and what changes the price if the builder finds worse ground or weaker walls than expected. Agree payment stages tied to visible milestones and keep every quote, invoice and certificate together [9].
Red flags
Prices a full extension from a phone description alone, without visiting, seeing drawings or checking ground conditions.
Starts structural work without telling you which building-control route the job follows [7].
Hands you a single lump sum with no breakdown of labour, materials and VAT [9].
Wants the whole price in cash up front before any written agreement exists [9].
Claims a scheme membership you cannot find when you search the register yourself [1] [2].
Brushes off party-wall notices where the work touches a shared wall or digs near a neighbour's foundations [3].
Will not put the scope, price, start date and payment stages in writing before starting [2].
The bottom line
For most people planning an extension in Telford, start with Randle Building Solutions: one established firm for the building work plus solar panels, heat pumps or charging points, with scheme membership on record and cover stated in figures. It publishes no rates, so ask for an itemised fixed quote and proof of cover before you agree anything.
Match the firm to the job where your brief is narrower. LMDS Architectural draws and steers the plans, Timber Kit Solutions supplies the timber frame your own builder raises, Rubik Builders owns energy-led retrofit work, and Tradestone paves and landscapes the ground around it all. Get two or three itemised quotes on the same written scope, and hold the final payment until the completion certificate is in your hands.
Corrections and business responses
Tell us what needs checking, or ask to claim a listing and reply to an assessment.