- Single storey rear extension (~20–30m²): Spruce £800–£2,100 | Larch £1,100–£3,000 | ThermoWood £1,500–£3,900 | Charred £1,900–£4,950 — all fully installed.
- Board cost per m²: Spruce £20–£35 | Larch £35–£65 | ThermoWood £55–£95 | Charred £75–£130.
- Installation: £20–£35 per m². London/South East add 25–35% to labour.
- Scaffolding: £600–£1,200 per elevation for installation. Required again every 2–3 years for spruce maintenance — totalling £7,500–£23,250 over 30 years.
- VAT: 20% on alterations to existing homes. 0% on qualifying new build. 5% where EWI is included.
- Fire rating: Required within 1m of a boundary — +£29.99/m² for Euroclass B-s1,d0 treatment.
The cost to clad a house extension is one of the most commonly searched questions by homeowners mid-project — and one of the most poorly answered. Most online guides quote board prices without addressing the critical hidden cost: scaffolding. On a house extension, every future maintenance visit requires scaffolding. If you specify treated softwood, you need scaffolding every 2–3 years. Over 30 years that is £7,500–£23,250 in access costs alone. This guide gives you complete honest pricing for 2026 — by extension type, by species, with scaffolding, VAT, regional variation, fire treatment, and profile choice all covered.
Why Species Choice Matters More on an Extension Than a Shed
When you clad a garden shed you can reach every board from the ground — maintenance is a half-day job with a stepladder. When you clad a house extension, the entire maintenance context changes. At 2.5–4m elevation, any maintenance activity requires scaffolding. That means £600–£1,200 every visit, before you buy a single tin of treatment.
Nordic spruce requires preservative treatment every 2–3 years. On a house extension, that is 10–15 scaffolding cycles over 30 years — £6,000–£18,000 in access costs alone, plus materials and labour. This number is almost never mentioned in cladding cost guides. It is the single most important figure in the whole-life cost calculation, and it is why ThermoWood and Siberian larch — which need zero scaffolding-dependent maintenance ever — are the only genuinely cost-effective specifications for house extensions when viewed over 10 years or more.
Cost by Extension Type — 2026 UK Prices
The claddable wall area varies significantly by extension type. Figures below use London April 2026 market rates — deduct 20–30% for labour outside London and the South East. All figures include materials, breather membrane, battens, A4 stainless fixings and installation. They exclude scaffolding, VAT and fire treatment.
| Extension type | Typical wall area | Spruce installed | Larch installed | ThermoWood installed | Charred timber installed |
|---|---|---|---|---|---|
| Single storey rear extension | 20–30m² | £800–£2,100 | £1,100–£3,000 | £1,500–£3,900 | £1,900–£4,950 |
| Kitchen extension | 15–25m² | £600–£1,750 | £825–£2,500 | £1,125–£3,250 | £1,425–£4,125 |
| Side return extension | 10–20m² | £400–£1,400 | £550–£2,000 | £750–£2,600 | £950–£3,300 |
| Two storey extension | 35–55m² | £1,400–£3,850 | £1,925–£5,500 | £2,625–£7,150 | £3,325–£9,075 |
| Wrap-around extension | 40–70m² | £1,600–£4,900 | £2,200–£7,000 | £3,000–£9,100 | £3,800–£11,550 |
Cost per m² — All Species Fully Broken Down
| Species | Boards/m² | Membrane + battens + fixings | Installation/m² | Total/m² | 30-yr maintenance/m² |
|---|---|---|---|---|---|
| Nordic Spruce | £20–£35 | £8–£12 | £20–£35 | £48–£82 | £240–£720 + scaffolding |
| Siberian Larch | £35–£65 | £8–£12 | £20–£35 | £63–£112 | £0–£10 (optional oil) |
| ThermoWood | £55–£95 | £8–£12 | £20–£35 | £83–£142 | £0 |
| Charred Timber | £75–£130 | £8–£12 | £20–£35 | £103–£177 | £0 |
The Scaffolding Cost — The Number That Changes Everything
This is the section most online cost guides skip. On a house extension, scaffolding is not a one-time installation cost — it is a recurring maintenance cost that multiplies every time you need to re-treat, repaint, or replace boards on the elevation.
| Species | Treatment frequency | Scaffolding per cycle | Materials + labour per cycle | 30-yr total maintenance |
|---|---|---|---|---|
| Nordic Spruce | Every 2–3 years | £600–£1,200 | £150–£350 | £7,500–£23,250 |
| Siberian Larch | Never required | £0 | £0 | £0 |
| ThermoWood | Never | £0 | £0 | £0 |
| Charred Timber | Never | £0 | £0 | £0 |
The upfront cost premium of ThermoWood over spruce on a 25m² rear extension is approximately £875–£1,500. The 30-year scaffolding-plus-treatment saving is £7,500–£23,250. The species upgrade typically pays for itself within the first maintenance cycle — approximately 2–3 years after installation. For any extension where you plan to stay for more than 5 years, ThermoWood or Siberian larch is the rational whole-life specification.
VAT — What Rate Applies to Extension Cladding?
VAT on cladding a house extension depends on the nature of the work — and it is one of the most misunderstood cost elements:
- 20% standard rate: Alterations and improvements to existing residential properties. This covers the majority of extension cladding projects — where cladding is being applied to an existing or new extension on an occupied house
- 0% zero rate: Qualifying new build residential construction only — where the building is constructed from scratch as a new dwelling. A retrofit extension on an existing home does not qualify
- 5% reduced rate: Available where the project includes fitting external wall insulation (EWI) under the energy-saving materials provisions. The insulation element may attract the reduced rate — the cladding boards remain at 20%
VAT rules are complex and individual project circumstances matter. Always confirm the position with your contractor and HMRC guidance before finalising your budget. The reduced rate for EWI requires specific qualifying conditions — do not assume it applies without confirmation.
Regional Price Variation — London vs Rest of UK
Timber cladding board prices are consistent nationally — we supply from Cambridgeshire to the same price anywhere in the UK. Labour and scaffolding costs vary significantly by region:
| Region | Installation labour/m² | Scaffolding per single elevation | vs Midlands baseline |
|---|---|---|---|
| London | £28–£45 | £900–£1,600 | +25–35% |
| South East | £25–£40 | £750–£1,400 | +15–25% |
| Midlands / East Anglia | £20–£32 | £600–£1,100 | Baseline |
| North of England | £18–£28 | £550–£950 | −5–10% |
| Scotland / Wales | £18–£30 | £550–£1,000 | −5–10% |
Fire-Rated Cladding for Extensions — When Required, What It Costs
Under Approved Document B, if any part of the extension wall is within 1 metre of a boundary, the external cladding surface must achieve at least Class B-s3,d2 reaction to fire performance. Our factory fire treatment achieves Euroclass B-s1,d0 — available on all species and profiles at +£29.99 per m². For extensions over 11 metres height, additional compliance requirements apply and a fire engineer should be consulted. See our fire-rated cladding for extensions guide, Approved Document B guide, and ThermoWood cladding cost guide.
Profile Choice and Its Effect on Cost
Within each species, profile choice adds 10–25% to board cost. Shadow gap and triple shadow gap dominate architect-designed extensions. Shiplap and feather edge suit traditional and barn-style projects.
| Profile | Cost vs shiplap baseline | Typical use on extensions |
|---|---|---|
| Shadow gap | +10–20% | Contemporary extensions — most specified |
| Triple shadow gap | +15–25% | High-end contemporary, architectural statement |
| Shiplap | Baseline | Traditional, barn-style, rural extensions |
| Feather edge | Baseline | Rural, agricultural character |
| Rainscreen open joint | +5–15% | Maximum ventilation, contemporary open-joint look |
How much does it cost to clad a house extension in the UK?
Single storey rear extension (20–30m²): spruce £800–£2,100 installed; larch £1,100–£3,000; ThermoWood £1,500–£3,900; charred timber £1,900–£4,950. Plus scaffolding £600–£1,200, fire treatment if required (+£29.99/m²), and 20% VAT on alterations. London labour adds 25–35%.
How much does it cost to clad a single storey rear extension?
A single storey rear extension typically has 20–30m² of claddable wall area. In Nordic spruce: £800–£2,100 installed. Siberian larch: £1,100–£3,000. ThermoWood: £1,500–£3,900. Charred timber: £1,900–£4,950. Plus scaffolding (£600–£1,200) and 20% VAT on alterations to existing homes.
What is the cheapest timber cladding for a house extension?
Nordic spruce is cheapest upfront at £20–£35/m². But on a house elevation requiring scaffolding maintenance every 2–3 years, the 30-year scaffolding-plus-treatment cost adds £7,500–£23,250. Siberian larch at £35–£65/m² with zero maintenance is typically cheaper whole-life, paying back the premium within 4–6 years.
Is VAT charged on cladding a house extension?
20% VAT applies to alterations and improvements to existing residential properties — the most common situation. Zero rate applies to qualifying new build. 5% may apply where external wall insulation is included in the same project. Confirm with your contractor and HMRC guidance before budgeting.
Do I need fire-rated cladding on a house extension?
If the extension wall is within 1 metre of a boundary, Approved Document B requires at least Class B-s3,d2 external cladding performance. Our fire treatment achieves Euroclass B-s1,d0 at +£29.99/m². Confirm with your building control officer before specifying.
Free Extension Cladding Quote — All Species, Fire Treatment, UK Stock
We supply ThermoWood, Siberian larch, charred timber and Nordic spruce for house extensions from UK stock. Fire treatment to Euroclass B-s1,d0 available on all species. Tell us your extension dimensions for a complete material cost and board quantity. Nationwide delivery 7–14 days.