Question 1

How accurate is a build cost calculator?

Accepted Answer

For a straightforward project on a standard South London property, a well-built calculator lands within about 15% of the final contract price. It cannot see what is under your floor, how your neighbour will respond to a party wall notice, or what the planning officer will ask for. Treat the range as a budgeting tool for deciding whether a project is viable, then get a survey before you commit to anything financially.

Question 2

Does the estimate include VAT?

Accepted Answer

Yes. Extensions, loft conversions and refurbishments on existing homes are standard-rated at 20%, and it is shown as its own line in the breakdown. Only new-build housing is zero-rated.

Question 3

Are architect and structural engineer fees included?

Accepted Answer

They are, under design and approvals. On an extension that line covers drawings, structural calculations, the planning or permitted development application, Building Control and party wall notices, and usually runs from GBP 6,000 to GBP 11,000. Fees paid directly to the council, and your neighbour's own surveyor if one is appointed, sit outside the figure.

Question 4

Why is there a range rather than one price?

Accepted Answer

Two identical 25 square metre extensions two streets apart can differ by GBP 25,000 on glazing, foundation depth and finish alone. The honest answer before a survey is a band, and then a fixed price once the drawings are settled.

Question 5

How much should I hold back as contingency?

Accepted Answer

Ten per cent of the total on a typical project, and closer to 15% on a Victorian property that has never been opened up. The most common reasons it gets spent are foundations that need to go deeper than expected, drainage in a different place to the plans, and decisions changed mid-build.

Question 6

Do I need planning permission, and does it cost extra?

Accepted Answer

Many rear extensions and rear dormer loft conversions fall under permitted development, which is quicker and cheaper. Full planning is normally needed for mansards, front-facing changes, work in a conservation area and anything beyond the permitted limits. Either route is covered inside the design and approvals line, though the council application fee is separate.

Question 7

Which parts of South London does AXE Construction cover?

Accepted Answer

AXE Construction works across South and South West London from a base in Streatham, including Clapham, Balham, Battersea, Wandsworth, Putney, Fulham, Wimbledon, Tooting, Dulwich, Sutton and Worcester Park.

Question 8

How soon can I get a fixed price?

Accepted Answer

AXE Construction usually surveys within five working days and returns an itemised written breakdown three to five days after that. The price becomes fixed once drawings and specification are agreed.

Build cost calculator

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