How long does a final account take?

Typical residential extension: 6–12 weeks post-completion. Larger or contested: 4–9 months. Drivers: documentation quality, response time, QS presence, variation complexity. JCT-administered with QS: 6–10 weeks. Self-administered: longer due to documentation gaps.

What's the retention percentage?

JCT Minor Works default: 5% (2.5% at practical completion, 2.5% at end of 6-month DRP). JCT Domestic similar. Some contractors agree lower (3%) on shorter projects; some clients insist on 10% for unfamiliar builders. Mid-market London 2026: 5% standard.

Can I withhold retention if there are snags?

Yes — point of retention. Withhold release until contractor addresses documented snagging. Issue formal certificate of making-good defects (or solicitor letter) before final retention release.

For projects over £150–200k, recommended. QS independent assessment prevents inflated variations, accurate measurement of provisional sums, mediates disputes. £2,500–£8,500 fee usually saves multiples in avoided overcharges.

Construction Final Account London 2026 | Builderr

What Is a Construction Final Account in London?

A construction final account is the formal statement at end of build summarising total contract value: original contract sum + agreed variations - omissions + adjustments = final account. In London residential, agreement typically takes 4–12 weeks post-completion; retention (5% withholding) released 6–12 months after practical completion. Disputes resolved via adjudication, mediation or arbitration.

What's in a final account

Original contract sum: agreed at signing — e.g., £180k fixed-price extension. Variations (instructed scope increases): each priced separately and added — e.g., upgraded windows £4.5k, additional rear opening £3.2k, larger island £2.8k = £10.5k variations. Omissions (instructed reductions): subtracted. PC (Prime Cost) sums and provisional sums: pre-set allowances reconciled against actual cost — positive or negative adjustment. Loss and expense claims (client-caused delay or unforeseen ground conditions): added if substantiated. Retention: 5% withheld at completion; half released at practical completion, half after 12-month DRP.

Agreeing variations

Each variation instruction (architect's instruction or written client request) generates a written variation order (VO) confirming: scope, agreed price, time impact. Best practice: variation priced before work starts (avoid cost-plus uncertainty). Common London disputes: variation discussed verbally but not priced/agreed in writing; client later disputes. Recommend JCT Minor Works or JCT Domestic with formal VO procedure. QS involvement: £2,500–£8,500 fee on £250k project saves £5–25k+ in disputed variations.

Defects, retention and snagging

Practical completion: handover; usable but typically with snags (cosmetic, finishing items). Snagging list documented at handover; contractor returns to address each — 4–8 weeks. Defects rectification period (DRP): 6–12 months; any new defects arising contractor returns to fix. Retention: 5% withheld; half (2.5%) released at practical completion (less snagging); other half at end of DRP with certificate of making-good defects.

Disputes and resolution

Resolution hierarchy: (1) negotiation — most resolved here; (2) mediation via RIBA or RICS £1,500–£4,500; (3) adjudication under Construction Act 1996 — 28-day timetable, decision binding pending court; £4,500–£12,000 fees; (4) arbitration (rare residential); (5) court (last resort; costs disproportionate). Most residential disputes settle at mediation. QS-administered contract + clear VO procedure + monthly applications for payment prevents 90% of disputes.