Case Study

Basement Conversion

Clapham, London

Basement excavation beneath a Clapham terrace with propping, ducting and an access ramp into the dig

Project type

Underpinned basement conversion

Contract value

£337,000

Programme

38 weeks

Retention

5% per sub-contract

James L. is the principal of a small development company that specialises in basement digs. At any one time he has two or three underpinned excavations running across South London, each a long programme of high-value, safety-critical work billed monthly. Before BuildFlow, his payment admin was a folder of spreadsheets that only he understood, and his biggest fear was paying against work he could not see, twenty feet below a house.

Connor B. is contracts manager at the groundworks and basement specialist delivering the job. His labour force sits inside the Construction Industry Scheme, and reconciling CIS deductions against certified payments used to be its own monthly job.

A bill that mirrors the engineering

The BoQ was structured around the engineer's underpinning sequence: pins in numbered batches, then the slab, waterproofing, and fit-out. Connor claimed each month against measured work, with photos from the dig attached to the pins and pours they evidenced. For work that is buried or tanked over within weeks, that photographic record against specific BoQ lines mattered to everyone, including the warranty provider.

James certified from the dashboard, comparing each claim against the previous month and the photos before approving. One month, with the slab pour behind programme, he issued a reduced certificate; BuildFlow tracked the pay-less notice deadline so the reduction was communicated inside the statutory window, documented, and accepted without friction.

CIS handled where the payment happens

BuildFlow calculated the CIS deduction on the labour element of every certified payment at Connor's verified 20% rate, showing gross, deduction and net on each certificate. Connor's office stopped re-deriving the figures in a spreadsheet, and James's accountant got a clean deduction record for the monthly CIS return.

Retention was held at 5% on the sub-contract and tracked automatically: half released at practical completion, the balance scheduled against the end of the defects period, both triggered deliberately rather than discovered in a year-old spreadsheet.

“Basement work gets buried. If you can't prove what you did before it disappeared under concrete, you're negotiating from memory. Every pin we claimed had photos on the line item, the CIS came out right on every certificate without my office touching a calculator, and when James reduced a valuation he did it properly, with notice, through the system. No drama.”

Connor B.

Contracts Manager, basement and groundworks specialist

CIS-registered labour force of 22

The portfolio view

This dig was one of three schemes on James's portfolio dashboard. Certified to date, paid to date, retention held and upcoming notice deadlines across every project sat on one screen, with each site pinned on the map. Month-end went from a weekend of reconciliation to a Monday morning review.

Monthly valuations across the dig

20%

CIS deducted and logged automatically

Live projects on one portfolio dashboard

“I'm certifying work I will never see again once it's tanked and backfilled, on three sites at once. BuildFlow gives me the evidence against every line, the statutory deadlines tracked for me, and the whole portfolio's payment position on one screen. I used to dread month-end. Now it's forty minutes with a coffee.”

James L.

Principal, basement development company

Three concurrent underpinned digs