House extension costs in Bristol: single-storey guide prices for 2026
£30,000 to £140,000. That is the honest range for a single-storey house extension in 2026, and it is that wide because it hides three different questions: how big, how much glass, and how much has to move underground before you build anything. Most people asking about house extension cost do not want the range. They want to know where their kitchen-diner in Bedminster or Bishopston sits inside it. So here are the numbers we, Dan and Craig, work to, the national benchmarks we check ourselves against, and the line items that push a quote up or down. Nothing here is a special deal. It is what things cost.
House extension cost per square metre in 2026
The national cost guides agree more than you would think. Checkatrade's 2026 extension guide puts a single-storey extension at £1,800 to £3,000 per square metre, with an average of £2,400 and a typical 30 m² build around £72,000. MyJobQuote's guide, updated June 2026, quotes lower build-only rates for basic finishes but lands its 20 to 30 m² examples at £44,000 to £60,000. Our own reading for Bristol in 2026: £1,900 to £3,200 per square metre for a standard specification, and £2,800 to £3,500 or more where the design is glass-heavy. Those figures are the build, excluding VAT and excluding the kitchen units.
| Single-storey extension | Typical size | 2026 guide band (build, ex VAT, ex kitchen) |
|---|---|---|
| Side return infill on a terrace | 8 to 12 m² | £30,000 to £45,000 |
| Rear extension, standard spec | 15 to 20 m² | £35,000 to £65,000 |
| Kitchen-diner rear extension | 25 to 35 m² | £55,000 to £110,000 |
| Wraparound or glass-heavy | 35 m² and up | £90,000 to £140,000+ |
The bands are the square-metre benchmarks multiplied out and rounded, not quotes. Small extensions sit at the top of the per-metre range because the fixed costs (scaffold, skips, drainage, steels, an engineer) do not shrink with the floor area.
Kitchen-diner extensions: the Bristol favourite
Most of the extensions we build are the same brief: a Victorian terrace with a narrow back kitchen and a dining room nobody eats in, and a family who wants one big room that opens to the garden. Structurally that means opening up the back wall on steels, a run of glazing, and usually rooflights so the middle of the house does not go dark. Maeve T. wrote on Google that we "completed a rear extension and remodel of the downstairs of our Victorian terrace which we are thrilled with", and that project write-up shows what the remodel part involves. The kitchen itself is its own line on the quote. The kitchen is priced on its own line, so you can see exactly what the units and worktops add. Our kitchen-diner project for a growing family is the other worked example.
[IMAGE: Rear kitchen extension under construction with anthracite bifold doors fitted | alt: Kitchen extension in progress with bifold doors fitted, a Wilson & Cole site in Bristol] (suggested file: extension-kitchen-bifolds-wip_16x9.jpg)
Side return vs rear extension on a terrace
| Side return | Rear extension | |
|---|---|---|
| Space gained | A 1.2 to 2 m strip along the kitchen; turns a galley into a wide room | 3 to 6 m out into the garden |
| Light | Rooflights or a glazed roof along the boundary wall | Rear glazing; rooflights needed to keep the middle room bright |
| Structure | A steel along the flank wall, often another where it meets the house | One or two beams across the back wall |
| Party wall | Line-of-junction notice one month ahead; party structure notice two months ahead if we cut into the shared wall | Notice for excavation within 3 m of next door's foundations, one month ahead |
| Planning (permitted development) | Up to half the width of the original house, single storey, max 4 m high; not on designated land | 3 m beyond the original rear wall (4 m detached), or 6 m/8 m with prior approval; max 4 m high, 3 m at the eaves within 2 m of a boundary |
| Guide band | £30,000 to £45,000 | £35,000 to £65,000 for 15 to 20 m² |
The planning limits are from the Planning Portal's extension guidance; the notice periods come from the Party Wall etc. Act 1996, and our Party Wall guide for Bristol terraces walks through the neighbourly version. On many BS3 and BS5 terraces the answer is both, a wraparound, which is where the £90,000-plus figures come from.
Steels, glazing, groundworks: the line items that move the number
Three things swing a single-storey extension quote more than anything else.
Steels. Opening a back wall needs an engineer's calculations and one or more beams. Checkatrade's RSJ guide puts a small beam at about £200 for the steel and £300 to fit, and a 5 m beam at about £950 plus £750 to install; a kitchen-diner opening can need two or three, plus padstones and temporary works. Longer spans, heavier sections and awkward access all add.
Glazing. A 3 m three-panel aluminium bifold runs £3,000 to £4,500 supplied and fitted according to Checkatrade's bifold guide, with the average aluminium set around £5,000; sliding doors, glazed roofs and big rooflights climb from there. Glass is where "standard" becomes "premium".
Groundworks and drainage. Foundations go deeper near trees and on clay, existing drains and manholes often sit exactly where the new room wants to be, and building within 3 m of a public sewer means a build-over agreement with Wessex Water. MyJobQuote's worked example of a £52,000 extension shows the shape of it: £8,000 on groundworks and foundations, £18,000 on structure and roof, £4,500 on windows and doors, £6,000 on plumbing and electrics.
On top of the build sit the fees: drawings, the engineer, building control, and a party wall surveyor if your neighbour appoints one, typically £700 to £1,500 per surveyor in 2026.
What our detailed, itemised quote includes
Every quote we give is detailed and itemised: groundworks, structure, roof, glazing, first and second fix, plaster and decoration, each on its own line, with provisional sums shown clearly for things you have not chosen yet, like tiles or the kitchen. Once you are in the diary we ask for a modest booking deposit of around 10%, never a large payment up front, and the rest is staged as the work goes in. VAT is 20% on most extensions; a reduced 5% rate applies to some work, such as renovating a home that has been empty for two years or more, and VAT Notice 708 has the detail, so ask us whether your project qualifies.
A single-storey extension takes us 10 to 16 weeks on site, and for most of it your kitchen is out of action; we set up a temporary one and seal the build off from the rest of the house, as described in how we keep your home liveable during a build. On value, Nationwide's research reported by Which? found that a 10% increase in floor area adds around 5% to a home's value, and our loft-or-extension comparison weighs that against a loft. If you want to compare quotes properly, the questions that separate good Bristol builders explains what an itemised quote should show; the house extensions service page has more of our work, and our written guarantees are on the FAQ page. We are Federation of Master Builders members with a 5.0-star Google rating from 25 or more reviews.
Frequently asked questions
How much does a 20 m² single-storey extension cost in Bristol?
Around £40,000 to £65,000 for the build in 2026, excluding VAT and the kitchen units, based on £1,900 to £3,200 per square metre. Glass-heavy designs, deep foundations and long steels push it towards the top; a simple rendered box with standard glazing sits nearer the bottom.
Do I need planning permission for a single-storey extension?
Often not. Permitted development allows a rear extension up to 3 m beyond the original wall (4 m on a detached house), or 6 m and 8 m with prior approval, no higher than 4 m, and a side extension up to half the width of the house. Conservation areas and flats need permission, and building regulations always apply.
How long does a single-storey extension take?
Ten to 16 weeks on site for a typical rear or kitchen-diner extension. Add around eight weeks if planning permission is needed and one to two months for party wall notices before work starts.
Does a kitchen extension add value to a Bristol home?
Nationwide's research suggests a 10% increase in floor area adds around 5% to value, and a well-planned kitchen-diner is the room buyers respond to most. The bigger uplift, up to 24%, comes from adding a double bedroom and bathroom, which is why we sometimes suggest a loft first.
Is VAT charged on a house extension?
Yes, at 20% for most extensions. A reduced 5% rate applies to some qualifying work, such as renovating a home empty for two years or more, and some energy-saving materials are zero-rated until 31 March 2027. Ask us whether your project qualifies.
We have capacity this year. Let's talk before it's gone. Send us your plans, or just a photo of the back of the house, through our contact page and we will call you back within one working day with a detailed, itemised quote to follow.
