Garden Room Cost UK 2026: What Builders Actually Quote

Every homeowner who calls about a garden room has already read one of the cost-guide sites. They'll quote you a number back - '£15k to £50k, right?' - like it means something. It doesn't. That range is wide enough to cover a flat-pack shed with a window and a fully kitted-out home office with underfloor heating. It's not a quote. It's not even close to one.

Forget the Range You've Read Online

A real quote isn't a single number pulled from a guide - it's a sum of parts, and the parts are what actually move the price: the foundation type, the frame, the cladding choice, how much glazing is in the front elevation, the electrics spec, and the internal finish. Two garden rooms the same size can differ by £10,000 depending on those choices alone.

Foundation

Ground screws typically run £30-£50 per m² for straightforward ground; a concrete slab is closer to £80-£180 per m². Sloped or clay-heavy ground pushes either option up - sometimes by thousands - before a single stud goes in. This is the line most likely to get underquoted because it's invisible once the room's up.

Frame, Roof and Glazing

A timber stud frame generally costs £350-£500 per m² in materials. Glazing is priced per opening rather than per m² - a standard window runs £500-£700, and a set of bifold doors (the usual choice for a garden-room frontage) is £1,800-£2,500 on its own. Frame, roof structure and glazing together are usually the single largest line on the quote.

Cladding

Timber cladding materials alone are around £50-£75 per m²; priced with labour, cladding (timber, composite or metal) typically lands at £170-£330 per m². The choice isn't just looks - metal and composite cost more up front but need far less maintenance than timber, which is worth saying to the customer before they pick on price alone.

Electrics

Basic wiring and a consumer unit connection is £800-£2,000; a full Part P certified installation (sockets, lighting, data points, certification) is more realistically £1,500-£3,500. This is a job for a qualified electrician, not a line to estimate loosely - the certificate is what makes the room legal to use, not just wired.

Internal Finish and Insulation

Insulation (floor, walls and roof together) is typically £1,500-£3,000 for a standard-sized room - it's one of the cheaper lines, which is exactly why it gets cut on budget builds, and exactly why those builds are only usable six months of the year. Internal fit-out on top of that ranges from £200-£400 per m² basic to £400-£800 per m² for a proper mid-range finish.

That total sits comfortably inside what cost-guide sites call a 'typical insulated garden room' - but notice it didn't come from a range. It came from six real decisions, each with its own cost. Change the cladding to metal, add a second bifold, upgrade the fit-out, and the number moves in a way you can actually explain to the customer - not just a bigger guess.

Why This List Still Gets Guessed

Nobody sits down and genuinely estimates all six of these from scratch on every job - there isn't time, so most builders carry a rough number in their head and adjust it by feel. That's the same guesstimating trap that eats margin on any job: the price in your head is six months old, and it was never broken down by line in the first place. The only way to quote a garden room properly, every time, without it taking an evening, is to have the breakdown built in.

This is exactly what PriceM8's Garden Rooms add-on does. One task prices the whole build - foundation, frame, cladding, roof, electrics and internal finishes - with the frame studs calculated at a fixed 400mm centres and cladding (cedar, larch, composite or metal) priced separately for the front and for the sides and back, because that's how it's actually specified and bought. It isn't a flat per-m² guess. It's the same six-line breakdown above, done automatically, every time.

It's a one-off £99 add-on on top of a Landscaping subscription, and your subscription includes 2 free Garden Room quotes to try it before you buy. See the full garden room estimating breakdown or check pricing.