Cost guide
House extension cost in Glasgow
Real guide figures for Glasgow properties in 2026 — per square metre, by extension type, and with the fees most quotes leave out.
Written byMichael Redwood, Construction & Technical Lead
Typical 20 m² build
£40k – £60k · 12 weeks
Glasgow · Scotland
180+
Glasgow extensions delivered
Warrant & completion certificate included
A house extension in Glasgow costs approximately £2,000 to £3,000 per square metre for a standard-specification single-storey build, excluding VAT, professional fees and kitchen or bathroom fit-out. A 20 m² rear extension therefore lands between £40,000 and £60,000 for the build alone, with total project cost typically 20 to 30 per cent higher once fees, VAT and finishes are included.
What drives the cost per square metre
Floor area sets the baseline. Complexity sets the rate. Two extensions of identical size in the same street can differ by £20,000 because of ground conditions, glazing and structural spans.
- Ground conditions — made ground, shallow Victorian foundations and mine workings in parts of the east and south of the city all increase groundworks cost.
- Structural spans — wide open-plan openings need heavier steel and sometimes padstones into existing sandstone.
- Glazing — a run of sliding doors or a structural glass corner is often the single largest line item after the shell.
- Drainage — moving an existing sewer or building over a public drain requires Scottish Water approval and adds cost and time.
- Roof form — flat roofs cost less than pitched; pitched roofs with rooflights and slate to match a sandstone home cost most.
- Access — a narrow tenement lane or a rear garden with no vehicle access adds labour to every material movement.
Guide costs by extension type
| Extension type | Typical size | Build cost range | Cost per m² |
|---|---|---|---|
| Single-storey rear | 18–25 m² | £40,000 – £70,000 | £2,000 – £2,800 |
| Side return | 10–14 m² | £28,000 – £45,000 | £2,400 – £3,200 |
| Wrap-around | 28–34 m² | £62,000 – £95,000 | £2,200 – £2,900 |
| Two-storey | 2 × 16–20 m² | £75,000 – £115,000 | £1,900 – £2,600 |
| Porch | 3–5 m² | £7,000 – £14,000 | £2,200 – £3,000 |
The costs quotes commonly leave out
Professional fees
Architectural design, structural engineering and warrant drawings typically total 7 to 12 per cent of the build cost. A structural engineer is not optional where you are removing load-bearing wall.
Statutory fees
A planning application fee applies where permitted development does not cover the works, and a building warrant fee is calculated from the value of the works. Both are paid to Glasgow City Council and both are separate from your builder's price.
VAT
Extensions to an occupied dwelling are standard rated at 20 per cent. Treat any quote that does not state its VAT position as incomplete.
Finishes
Kitchens, sanitaryware, flooring and joinery are usually priced separately. A mid-range kitchen in a new extension typically adds £12,000 to £25,000.
Budget the whole project, not the shell
Take the build cost range, add 10 per cent for fees, add 20 per cent VAT, then hold a further 10 to 15 per cent as contingency. That total is the number your bank or savings need to cover.
Is an extension worth it in Glasgow?
An extension adds value where it corrects a functional shortcoming — a cramped rear kitchen, a missing ground-floor WC, a two-bedroom home in a three-bedroom street. Value uplift is capped by the ceiling price of the street, which varies sharply across the city. Spending £90,000 on a property in a street with a £250,000 ceiling rarely returns the outlay; the same spend in Bearsden, Newton Mearns or the West End often does.
Frequently asked questions
What is the cheapest way to extend a house in Glasgow?
A simple rectangular single-storey rear extension with a flat roof, standard rooflights and no relocation of drainage is the lowest cost per square metre. Complexity — glazing runs, steel spans, level thresholds and drain diversions — is what raises the rate, not floor area alone.
Does a two-storey extension cost twice as much?
No. A two-storey extension typically costs around 60 to 75 per cent more than the equivalent single-storey, not double, because the foundations, roof and groundworks are shared across two floors.
Do I pay VAT on a house extension?
Yes. Extensions to an existing dwelling are standard rated at 20 per cent VAT. Certain conversions and properties empty for over two years can qualify for a reduced rate, which should be confirmed with HMRC guidance and your accountant.
What contingency should I hold for a Glasgow extension?
Hold 10 to 15 per cent of the build cost as contingency. Older Glasgow properties commonly reveal shallow foundations, unrecorded drainage runs and sandstone repairs once the ground is opened up.
Single-storey vs two-storey
Which gives more usable space for the money on a Glasgow plot.
Planning permission in Scotland
Whether your extension needs an application at all.
Building warrant explained
The Scottish approval you cannot start work without.
The build process
Stage by stage, with realistic timings.
Want a costed range for your property?
Tell us about your property and what you want to gain. We will talk you through the realistic cost, the planning route and the build sequence — no obligation.