What a builder's quote for an extension should actually include

Groundworks and foundations

The quote should state the foundation type and the assumed depth, and explain what happens if ground conditions differ. Excavation, spoil removal and any drainage alterations belong here. If a drain runs under the footprint, look for how it is dealt with.

• Foundation type and assumed depth
• Muck-away and skip allowance
• Drainage diversions or new connections
• What happens if deeper foundations are needed

Structure: walls, floor, steels and roof

Look for the wall construction (blockwork, cavity, insulation type), the floor construction and the roof structure and covering. Where the extension opens into the house, the steel or beam and the removal of the existing wall should be listed, together with who supplies the structural engineer's calculations.

If the roof has a lantern or rooflights, they should be named. For flat roofs, the covering system should be stated rather than just 'flat roof'.

Windows, doors and glazing

Glazing is often one of the largest single items. A good quote says whether bi-folds, sliders or French doors are included, the frame material and who supplies them. If it says 'client to supply', you need to budget separately.

First fix, plastering and second fix

Electrics, plumbing and heating are usually subcontracted. The quote should say how many sockets, lights and radiators are allowed, or state a provisional sum. Plastering, skirting, architraves and internal doors complete the internal finish.

• Number of sockets, switches and light points
• Heating: radiators or underfloor, and who connects it
• Plastering to walls and ceilings
• Second fix joinery and internal doors

Finishes and what is excluded

Kitchens, flooring, tiling and decoration are the items most often left out of an extension quote and then assumed by the homeowner to be included. A clear exclusions list is a sign of an honest quote, not a mean one.

Provisional sums and prime cost items

Some things cannot be priced exactly until work starts — deeper foundations, the condition of a wall once plaster is off. These should be shown as provisional sums with a stated amount, so you can see where the final figure could move. Prime cost sums cover items you have not chosen yet, such as sanitaryware.

Approvals, programme and payments

The quote should say who handles building control submissions and inspections, and whether planning drawings are included or provided by your architect. It should give a realistic programme and a payment schedule tied to stages of work, not dates.

Anthony runs our extensions directly, so the quote also tells you who is on site and who your single point of contact is.

Common questions