How much does a double-storey extension cost?
Last reviewed July 2026
A two-storey extension adds bedrooms and bathrooms as well as ground-floor space, and it spreads the cost of footings and roof across far more square metres, which usually makes it better value per m². Here’s what affects the cost.
The short answer
It depends on the size, the spec and how much structural work is involved, so there’s no reliable figure to put online. What we can say is that a two-storey extension usually gives you better value per square metre than a single-storey one, because the expensive footings and roof are shared across two floors. We give you a fixed written price for free after a visit.
What affects the cost
Every job is different, so we don’t put a figure on this page that we’d then have to caveat. These are the things that move the price up or down. The only accurate number is a measured written quotation, which we give for free.
Why the per-m² value is better
Footings and the roof are among the priciest elements of any extension. A two-storey extension uses the same footprint of foundations and roof to deliver two floors of space, so you get more house for each pound spent.
Matching the existing house
A convincing two-storey extension has to match brick, mortar and roofline across a bigger, more visible area. This is where bricklaying skill earns its keep. A good match reads as original; a poor one is obvious from the street.
Structural work and disruption
Two-storey work usually means more structural openings, more scaffolding and more time with the house opened up, all of which factor into the price and the programme.
Common questions
- Is a two-storey extension better value than single-storey?
- Per square metre, usually yes. The expensive foundations and roof are shared across two floors. If you need bedrooms as well as living space, it’s often the smarter spend, and we’ll quote both so you can compare.
- How long does a two-storey extension take?
- Typically a few months on site, depending on size and spec. We give you a week-by-week programme with the quote so you know what’s happening when.