How much does it cost to build a 100m² house?
Short answer
Applying Build It magazine’s 2026 cost per m² figures to 100 m² of gross internal floor area gives a construction cost of roughly £250,000 to £300,000 for an average self build. A simple, self-managed build could be nearer £220,000, and a high-spec one £320,000 or more. That is the cost of building the house only, before land, fees, connections and contingency.
The arithmetic
Build It’s 2026 guide puts the average self build at £2,500 to £3,000 per m² of gross internal floor area (GIA), with cost-conscious simple builds from about £2,200 and high-end builds above £3,200. Multiplying those rates by 100 m²:
| Level | Build It 2026 rate per m² | x 100 m² |
|---|---|---|
| Low (simple, self-managed) | about £2,200 | about £220,000 |
| Typical (average self build) | £2,500 to £3,000 | £250,000 to £300,000 |
| High (high-end detailing) | £3,200+ | £320,000+ |
These figures are our arithmetic on Build It’s published rates, not quotes. Construction cost only, and they say nothing about how VAT applies to your project.
What a 100m² home usually looks like
At 100 m², people are typically building one of these:
- A two or three bedroom bungalow. Single storey living is a common reason to build at this size, especially for downsizers.
- A compact two storey, two or three bedroom house.
- An annexe or a home on a tight plot, where the planning permission or the site limits the footprint.
Why small homes can cost more per m²
Some costs barely change with size. You need a kitchen, at least one bathroom, a heating system, utility connections, a warranty, design work and planning whether the house is 100 m² or 250 m². On a small house those fixed costs are spread over fewer square metres, so the rate per m² often lands higher than on a bigger home of similar spec.
Bungalows add their own twist. A single storey home of 100 m² has a bigger footprint than a two storey house of the same area, so it needs more foundation and more roof for the same floor space. Those are two of the more expensive parts of a build. If you’re comparing a bungalow and a two storey design, expect the bungalow to cost more per m², not less.
So for a 100 m² home it’s sensible to plan nearer the upper half of the band unless your spec is genuinely modest.
What’s not in these figures
- The land, and the tax and legal costs of buying it
- Architect, engineer, surveys, planning and building control fees
- Structural warranty and site insurance
- Water, power, drainage and broadband connections
- Driveway, landscaping and any garage
- Finance costs and where you live during the build
- Contingency: Penrith Building Society asks for evidence of a 15% contingency
The full checklist is in what’s not included in the cost per m².
How to refine your 100m² estimate
- Confirm the floor area. On a small house, a few extra square metres is a bigger share of the total. Make sure 100 m² is the internal area on the drawings, not a rounded target.
- Decide early on the kitchen and bathrooms. At this size they are a large part of the budget. A mid-range kitchen versus a high-end one can move the total noticeably.
- If it’s an annexe, check what’s shared. Using the main house’s drainage or power supply can save money, but get the connection routes checked before you count on it.
- Check the footprint against the ground. A bungalow’s wider footprint means groundworks findings have more effect. Get a ground investigation before you firm up the budget.
- Get quotes against the same scope. Compare quotes line by line so you know what each one includes.
How Self Build Budget helps
The free ranged estimate takes your floor area, quality level and region and gives you a low and high figure, with the high end as your planning figure. On the Standard plan you can then break that into UK build stages and replace estimates with quotes and payments as they come in, so you can see if a small build’s fixed costs are pushing the total up.
Questions people also ask
Can I build a 100m² house for £200,000? That’s below the lowest rate in Build It’s 2026 guide when applied to 100 m², before land and fees. It would need a very simple design, a modest spec and a lot of self management, and even then it’s tight.
Is a 100m² bungalow cheaper than a 100m² two storey house? Usually not. The bungalow needs more foundation and roof for the same floor area.
How many bedrooms fit in 100m²? Two or three is typical, depending on layout and how much space goes to living areas.
Does 100m² include the walls? Build It’s per m² rates are on gross internal floor area, which is measured inside the external walls.
Sources
- Build It: How much does it cost to build a house in 2026? (published July 2026, updated October 2026)
- Penrith Building Society: Self build and renovation mortgage scheme