1. A provisional sum is an estimate, not a price
A provisional sum (sometimes "PC sum" or "allowance") is a placeholder the builder includes in a quote when the exact cost isn't yet known. It's an honest "we'll spend roughly this much" — not a fixed price.
2. Why builders use them
Some items genuinely can't be priced up front: a kitchen the homeowner hasn't chosen yet, electrics that depend on layout, tiling that depends on which tiles are bought. Provisional sums let the quote move forward without inventing a fake fixed price.
3. Why they can hurt UK homeowners
In practice, provisional sums almost always go up, rarely down. A low provisional sum can make a builder's overall quote look competitive on paper, then drift higher once real decisions are made.
4. Common provisional sums to watch for
- Kitchen supply allowance
- Bathroom sanitaryware and tiles
- Flooring (especially engineered wood and large-format tiles)
- Electrics and lighting
- Bifold or sliding doors
- Decoration and second fix joinery
- Drainage diversions
5. How to keep them under control
- Get them quoted properly before you sign, not after
- Specify the products you actually want
- Ask the builder what realistic high/low range looks like
- Track each provisional sum against actual spend in writing
- Agree how variations to provisional sums get approved
6. Provisional sums vs variations vs extras
A provisional sum is an allowance in the original quote. A variation is a change to the agreed scope. An extra is work outside the original scope. All three should be priced and signed off in writing before they happen.
7. The questions to ask before you accept
Send the builder a short, polite email: which lines are provisional sums, what assumptions are they based on, what's the realistic upper limit, and how will any overspend be agreed? The Homeowner Quote Checker Pack includes a provisional sums tracker and a clarification email template. The free Builder Quote Checklist covers the basics if you only have one quote in front of you.
Use this on your actual project
The free Builder Quote Checklist gives you a short printable pack to sanity-check any UK builder quote. The Homeowner Quote Checker Pack goes further with the exact ground covered in this article.
The Builder's Brief UK provides practical homeowner guidance based on real trade experience. It is not legal, financial, architectural, structural engineering, planning or building-control advice, and is not a replacement for project-specific guidance from suitably qualified professionals.