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What changes the price of building work?

The size of the job is only part of the picture. Two extensions with similar floor areas can need different foundations, access arrangements and finishes. An early budget estimate is easier to compare once each builder has the same drawings and description of the work.

• The existing building: its condition, what needs removing and whether further investigation is needed before a firm price can be given.
• Plans and specifications: the structure, layout, insulation, windows, doors and finishes you want.
• Access and site arrangements: room for deliveries, scaffolding, skips and storage, and whether you will be living at home during the work.
• Other trades: who will arrange plumbing, electrical work, plastering and decorating, and whether their charges are included.
• The point at which the job ends: a weatherproof shell, a plastered room and a room ready to use are different scopes of work.

Give each builder the same starting point

You can ask for help before every detail is settled. Say which decisions are still open so the builder can explain what they need to check. Once you are ready for detailed quotes, share the same information with everyone you approach:

• What you want built or changed, with drawings and specifications where available.
• Your preferred materials and finishes, including anything you will buy yourself.
• Which rooms need to stay usable, and any restrictions on access, parking or working hours.
• Your preferred timing and whether you need help arranging other trades.
• Which permissions, design work and inspections have already been discussed or arranged.

What should a written builder’s quote include?

• The agreed work: drawings or a clear description, materials and the finish you should expect.
• The price: labour, materials, VAT where applicable, and any allowances or exclusions shown separately.
• Practical arrangements: deliveries, scaffolding, waste removal and protection of the parts of your home being kept.
• Timing and payments: a proposed start, the main stages and when payments are due.
• Changes and completion: how extra work will be priced and agreed, and how you will record any items still to finish.

Is it a quote or an estimate?

A quote gives an agreed price for specified work. An estimate is an indication of the likely cost and can change. Ask which you have received, what assumptions it uses and which items still need a firm price. Keep the agreed details in writing.

Before work begins

Agree who will check permissions and arrange any required inspections. Planning permission and building regulations approval are separate matters; the requirements depend on the work and where you live. Check with the relevant local authority rather than assuming the quote covers every approval.

For a larger project, ask the builder to explain the sequence of work and the points when you will need to make decisions. A final walk-through and a written list of unfinished items can help everyone agree what remains to be done.

For more detail, see Citizens Advice on arranging work at home and GOV.UK’s building regulations guidance. These pages explain the rules in England and link to guidance for other parts of the UK.