In short
The two cost much the same per m², with timber frame often a little cheaper on paper, and every builder knows brick and block. Timber frame is faster, gives thinner walls for the same insulation and copes better with a winter start. For most single-storey rooms the finished result is the same, so choose on programme and on which builder you trust.
On this page
Strip away the sales talk and the two methods differ in one layer of the wall. The foundations, the roof covering, the windows and everything inside are identical. So the comparison is narrower than it first looks.
Side by side
| Timber frame | Brick and block | |
|---|---|---|
| Typical cost per m², including VAT | £1,400 to £2,400 | £1,800 to £3,000 |
| Shell weathertight | About 2 weeks after the slab | A month or more after the slab |
| Wall thickness at 0.18 W/m²K | 250 to 280 mm with board or render | 330 to 350 mm |
| Building in frost and rain | Carries on | Mortar cannot be laid in frost |
| Changes once work has started | Costly after panels are made | Easier, block by block |
| Hanging heavy things | Needs backing boards planned in | Fix anywhere |
| Builders who do it | Fewer, more specialised | Almost all |
These are typical national ranges for 2026 for a single-storey extension, including VAT. London and the South East usually cost 20 to 40% more. A guide, not a quote.
Cost
On paper, timber frame often comes out a little cheaper per m². In practice the gap is smaller than the two ranges suggest, because the ranges overlap and the finish, glazing and roof cost the same whichever way the walls go up.
Time also has a price. Scaffold, a site toilet and a skip are hired by the week, and so, in effect, is the builder. A job that finishes a month sooner costs less to run. If you are renting while the work is done, add the rent.
For a small plain room, a good bricklayer will be cheaper. For a larger extension with wide glazing, the two usually come out within a few per cent of each other. The cost calculator shows both figures for any size.
Speed
This is the real difference. Blockwork goes up in lifts of about 1.5 m, each needing time to cure, and stops in heavy rain or frost. A timber frame is made indoors while the groundworks are done, then stood in days.
Getting the roof on early has a second effect. Electricians, plumbers and plasterers can start inside while the cladding goes on outside, instead of queueing behind the bricklayer. And a dry shell does not need weeks to dry out before floors and paint.
The catch is lead time. Panels take four to eight weeks to draw and make, and the design has to be frozen before that clock starts.
Space and warmth
Both walls must meet the same insulation standard. A timber frame holds its insulation between the studs, in space a masonry wall fills with block, so it reaches the target in less thickness. With board or render cladding the saving is 70 to 100 mm on every external wall. On a 6 m by 4 m room that is roughly a square metre of extra floor.
Add a brick skin to the frame and the advantage disappears.
Masonry stores heat and releases it slowly, which evens out summer temperatures. A lightweight room with a lot of south-facing glass warms up faster, so give it shading or opening rooflights.
Noise and solidity
Mass stops sound. A brick and block wall is better than a bare stud wall at keeping out traffic rumble. A frame with a brick outer skin, or two layers of dense plasterboard inside, gets close.
Inside, stud walls sound hollow if you knock on them. Some people mind. They also need plywood backing wherever a kitchen unit, radiator or television will hang, which has to be decided before plastering.
Lifespan, mortgages and resale
A timber frame kept dry will outlast its owners. Warranty standards work to a structural life of at least 60 years, and the frame is protected by a membrane, a ventilated cavity and treated timber at the base. Brick is more forgiving of neglect: a blocked gutter soaks a brick wall for years before anything rots.
Lenders and insurers treat modern timber frame as standard construction, especially with a brick or rendered face. Buyers rarely know, or ask, how an extension was built. What they and their solicitor want is the building regulations completion certificate, and that is the same piece of paper for both.
Planning
Planning rules do not distinguish between the two. What they care about is what the outside looks like. A boarded extension on a brick house falls outside permitted development whichever structure is behind the boards.
Which to choose
Choose brick and block if the extension is small and simple, if your preferred builder works that way, or if you expect to change your mind as you go.
Choose a timber frame extension if you are going up two storeys, starting between October and March, short of width on the plot, or simply want the disruption over sooner.
Either way, pick the builder before the method. A good one will build well in whichever they know best.