Small orangery cost

Multiply the floor area by the rate for the frame: £850 to £2,000 per m² for uPVC, £1,600 to £2,500 for aluminium and £2,000 to £3,000 for hardwood. At this size, plan on the upper half of each range rather than the lower.

The table does the sums for three common small footprints. Like every figure on this site, they are national, include VAT, and run 20 to 40% higher in London and the South East; the orangery cost calculator covers larger rooms too.

Some costs arrive whatever the size. The crew, the skip and the scaffold come for a 9 m² room as they would for a 24 m² one. The junction with the house needs the same flashing, the same damp-proof detail and usually the same lintel or beam. A lantern half the length is not half the price, because the kerb, the ridge and the fitting labour barely change.

Paperwork does not scale down either. Building control charges for a single-storey extension of 10 to 40 m² are about £700 to £1,100 including VAT, and each council sets its own. Drawings and structural calculations cost much the same for a small room as a medium one.

Spread over fewer square metres, those fixed costs push the rate up. That is why a 4 × 4 m room often costs only a little more in total than a 4 × 3 m one, and why adding a metre at the design stage can be the best value in the job.

Proportion matters more than area. Keep the floor level with the house so there is no step at the opening. Run the glazing down to the floor on the garden side. Choose slim frames: aluminium sightlines are narrower than uPVC, and in a small room the difference shows.

Size the lantern to the room, not to the budget. On a 3 × 3 m orangery a lantern of about 2 × 1 m leaves a plastered border wide enough for downlights while putting daylight over the middle of the floor. Where full building regulations apply, which for an orangery is almost always, rooflights need a U-value of 2.2 W/m²K or better, and solar-control glass is worth having on any roof that gets afternoon sun.

Think about the doors you already have. If the existing back doors open into the orangery, the room borrows the space behind them. Replacing them with a wider opening costs more but turns two small rooms into one usable one.

A room that projects 3 m or less fits the permitted development depth for any house in England, detached, semi or terrace, so many small orangeries need no planning application. The height limits still apply: no more than 4 m overall, and eaves no higher than 3 m within 2 m of a boundary. On a narrow plot that eaves limit is the one to watch.

Small does not mean exempt from building regulations. The conservatory exemption depends on at least three quarters of the roof being glazed, and a solid orangery deck falls short at any size.

On a terrace or a semi the foundations will usually be close to the neighbour. If they come within 3 m of the neighbour’s building and go deeper than its footings, the Party Wall Act requires written notice before work starts.

A 3 × 3 m room holds a table for four or a pair of chairs, not both. If the plan is a kitchen with an island and a dining table, you need nearer 20 m², and the price per square metre falls as the room grows. Test both sizes in the calculator before deciding.