4m x 3m conservatory cost: what the job involves and who is registered to do it

How 4m x 3m conservatory cost works

1. Understand what twelve square metres does to the fixed costs. Excavation, the concrete, the damp proof membrane, the opening into the house and the day the fitters lose to setting up do not shrink much with the footprint. On a room this size they are a large share of the total, which is why halving the floor area does not halve the price and why a slightly larger room often looks better value per square metre.
2. Decide the roof pitch early on a 3m projection. Three metres out from the house is where the roof shape starts to matter. A lean-to has to clear the ground floor windows above it and still shed water, and on a bungalow or under a low eaves that gets tight. A hipped or Victorian roof buys height but costs more in bars, glass and labour, and it changes the frames underneath.
3. Check where you sit against the exemption threshold. The conservatory exemption has a floor area limit, and twelve square metres is comfortably inside it, which is one of the reasons this size is so common. That keeps the room outside the full thermal requirements as long as the separating doors stay in place and the heating is not extended into it.
4. Price the glazing area, not the floor area. A conservatory of this size is mostly glass, so the unit specification matters more than the footprint. Solar control coatings on the roof glass and a sensible make up in the side frames are what decide whether the room is usable in July, and that decision is worth more here than an extra half metre of floor.

Insurance and paperwork

Common questions

Is 4m x 3m big enough for a dining table?

Twelve square metres takes a table for six comfortably if the doors from the house open into the house rather than into the room, and much less comfortably if they do not. Draw the door swings before you settle the size, because that decision is cheap on paper and expensive afterwards.

Will a room this size need a structural opening in the house wall?

Only if you want one. If the conservatory connects through an existing patio door opening the wall is untouched, and if you want the opening widened it becomes structural work with a calculation and a lintel of its own. That is the single largest optional cost on a room this size.

Does the shape matter as much as the area?

Yes. A 4m by 3m room is a different building from a 6m by 2m room with the same area, because the perimeter and therefore the frame count and the glass area are different. Price is closer to perimeter than to floor area at this scale.

Registered contractors by region

• Registered roofers in the East Midlands postcode area
• Registered roofers in the East of England postcode area
• Registered roofers in the London postcode area
• Registered roofers in the North East postcode area
• Registered roofers in the North West postcode area
• Registered roofers in the Scotland postcode area
• Registered roofers in the South East postcode area
• Registered roofers in the South West postcode area
• Registered roofers in the Wales postcode area
• Registered roofers in the West Midlands postcode area
• Registered roofers in the Yorkshire and The Humber postcode area