Quick answer

The costs most often missing from building quotes are professional fees (design and structural engineering), council and building control fees, party wall surveyors, drainage work and build-over agreements, skip and parking permits, temporary works, kitchen and finishes left as “client supply”, decorating, landscaping, VAT and a contingency for hidden conditions. A low quote that leaves these out can end up the most expensive option. Ask for an itemised quote with a clear list of exclusions.

Prohaus guidesProhaus Ltd, Kingston upon Thames
Updated October 20265 min read
Building work in progress with a temporary steel stair and exposed structure, Florian Road, Putney
Florian Road, Putney: structural work in progress
12 items
often missing from cheap building quotes

Key takeaways

  • Compare quotes by what they include, not by the total.
  • Professional, approval and party wall costs sit outside most build prices.
  • “Provisional sums” are guesses. The more there are, the less certain the price.
  • Period houses need a contingency.
  • A written contract should say how changes are priced before they happen.

01The 12 hidden costs

# Cost Why it gets missed
1 Architect or designer fees Often arranged separately by the homeowner
2 Structural engineer Needed whenever walls are removed or steel is used
3 Planning or prior approval fees Only needed for some projects, so often forgotten
4 Building control fees Required for almost every extension and loft
5 Party wall surveyors Only needed if a neighbour does not consent
6 Drainage diversion and build-over agreements Drains are not visible until digging starts
7 Skip, scaffold and parking permits Council licences on the road or pavement
8 Temporary works and protection Propping, dust screens, floor protection
9 “Client supply” items Kitchen units, sanitaryware, flooring, light fittings
10 Decorating and making good Sometimes stops at “plastered ready for decoration”
11 Garden and landscaping Paths, steps, patios and fences after the build
12 VAT and contingency Quotes shown without VAT, and no allowance for surprises

Swipe the table sideways to see every column.

1 and 2: Design and engineering

Planning drawings, building regulations drawings and structural calculations are essential for most extensions and lofts. Prohaus works closely with professional architects, designers and structural engineers through our planning and design service.

3 and 4: Approvals

Planning or prior approval fees are paid to the council. Building control fees are paid to the council or a registered building control approver. See our planning permission guide.

5: Party wall

If a neighbour does not consent in writing, surveyors must be appointed, and the building owner usually pays both. See our Party Wall Act guide.

6: Drainage

Side returns and rear extensions often sit over drains. Diverting them, adding access chambers or agreeing a build-over with the water company adds cost.

7: Permits

Skips and scaffolding on the road or pavement need council licences. Parking suspensions for deliveries are common on terraced streets in Fulham, Putney and Clapham.

8: Temporary works

Propping the house while steel goes in, protecting floors and stairs, and sealing off dust are real costs that a good quote includes.

9 and 10: Finishes

Check who supplies and pays for the kitchen, bathroom fittings, flooring, light fittings and decorating. Two quotes can differ simply because one includes them.

11: Outside

The garden is often damaged during a build. Levels, steps and paving outside new doors should be planned with the extension, as on our Park Way project on the Wimbledon page.

12: VAT and contingency

Prohaus guide prices are shown plus VAT. A contingency covers conditions that cannot be seen before work starts, especially in older houses.

Ground-screw foundations being installed for a garden office, Maple Road, Surbiton
Maple Road, Surbiton: ground-screw foundations going in

02What is a provisional sum?

A provisional sum is an allowance in a quote for work that cannot be fully priced yet, for example “£X for drainage”. The final cost may be higher or lower. A quote with many provisional sums is less certain than it looks. Ask how each one was estimated.

House exterior during building work, with new glazing and site hoarding, Florian Road, Putney
Florian Road, Putney: building work under way

03How to protect your budget

  1. Ask for an itemised quote with a list of exclusions.
  2. Fix the design and specification before pricing.
  3. Check every quote covers the same scope.
  4. Keep a contingency for the age and condition of the house.
  5. Agree in writing how changes (variations) are priced before they are carried out.
  6. Read our guide to itemised and lump-sum quotes.

At Prohaus, every project starts with a site visit, a detailed and transparent itemised quotation, and a written, agreed contract.

04Frequently asked questions

How much contingency should I allow?

It depends on the age and condition of the house and how much is known before work starts. Older houses with lots of structural and services work need a larger allowance than a new extension on a modern house.

Why are quotes so different?

Usually because they cover different scopes, specifications or exclusions. Compare them line by line.

Is the builder responsible for building control?

It should be agreed in writing who applies to building control and who pays the fees.

Do extension prices include the kitchen?

Often not. Check whether the kitchen is included, and if so, which units and appliances. See our kitchen and bathroom cost guide.

About Prohaus

Prohaus Ltd is a building company based in Kingston upon Thames, registered in 2015 and built on more than 20 years of residential building experience. We carry out extensions, loft conversions, renovations, new builds, kitchens and bathrooms, glazing, bespoke joinery and garden offices across Kingston, Surbiton, Richmond, Barnes, Putney, Fulham, Chelsea, Clapham and Wimbledon. Every project runs under a written contract with a 1-year guarantee.

Sources

Get a clear, itemised quote

Send us your address, drawings if you have them, and what you want to build. We will visit and provide a written, itemised quotation with exclusions listed.

07960 958286Use the contact form info@prohaus.co.uk