Family room extension cost in 2026

Question

We are in a detached house and have some space down the side which I think it'd be possible to use to add a metre or so to the lounge area. How much does a family room extension like this cost? Just need an average number at this point from the pros!

Omid · Answer

Hi it’s cost about £2500 per square meter first fix and second fix it’s on you

Alistair · Answer

Hi it’s cost about £2500 per square meter first fix

Kevin · Answer

Depending on square meters of the project and the opening you would like to create in to the main house it’s hard to give an accurate price 
Most construction companies will charge 2k a square meter depending on how complex and how far you would want to go with the project hope this helps

Alex · Answer

Average cost per square metre:
• A single-storey extension typically costs roughly £1,800 – £3,000 per m² of new internal space. The exact figure varies by location, quality of finish and complexity — and costs in the South East (including Kent) tend to be toward the higher end of the national range.

📏 Example Budgets

If you’re extending the lounge a bit sideways — say adding:
👉 10 m² (small): approx. £18,000 – £30,000
👉 15 m² (medium): approx. £27,000 – £45,000
👉 20 m² (larger): approx. £36,000 – £60,000

These are very rough averages covering labour and basic materials only. Planning fees, architect/structural engineer costs, VAT (20%), and anything bespoke (like bi-fold doors, high-end finishes, structural work) are on top.

Craig · Answer

So to dig out foundations Concrete build put on Roof  timber and tile Totton dab plastering electrics, plumbing Screed floor fit Windows £2000 a square meter

Kim · Answer

Depending on your location. But normally £2,500 + vat per square metre

Edmund · Answer

🧱 Typical Cost Ranges (UK 2025–26)
📏 Cost per square metre (single-storey extension)
• Low/standard build: £1,800 – £2,200 per m²
• Mid-range: £2,200 – £2,700 per m²
• Higher-spec/premium: £2,700 – £3,300 per m²
(These are typical build + labour costs — VAT and fees extra) �
SECalcs
📍 Side extensions specifically
• A single-storey side extension often comes in around £1,900 – £3,000 per m² depending on quality and complexity. �
SECalcs +1
📌 Rough Budget Examples
Let’s say you want to add about 1 m extra width to your lounge:
If your lounge runs ~4–5 m deep, that’s ~4–5 m² extra floor area.
Applying typical costs:
£1,800 × 4 m² = ~£7,200 up to
£3,000

Thanks
Eddie

Rick · Answer

It depends on the existing house structure (brick or render etc) .
1500 - 2000 per square meter

Dale · Answer

Depending on location,  access, finished article,  between £2100 -£2500.sqm

Dean · Answer

£3000 per sq metre at least. To be honest, for an additional 1 metre's width in the living room, it would be more cost effective to build a fully powered, fully insulated garden room giving you much more space.

Family room extension cost in 2026

Follow Us

Cookies

Manage Cookies

Essential cookies

Analytics & Tracking

Advertising