How Much Should I Pay My Builder Upfront? A Stage Payment Guide for UK Extensions

You have found a builder, agreed the work, and now they want payment. But how much should you pay upfront? When should the rest be due? And what is fair for both sides?

This is the most common question homeowners ask when planning an extension, loft conversion, kitchen or bathroom. Get it right, and the project runs smoothly. Get it wrong, and you are either chasing a builder who has disappeared with your money, or your builder is carrying thousands of pounds of unpaid work.

Here is a clear, stage-by-stage guide to payment schedules for the most common UK building projects.

The golden rule: pay for work done, not work promised

Stage payments should be tied to completed milestones, not calendar dates. When a builder says "I need £5,000 next Friday," the right question is: "What milestone will be complete by then?"

This protects both sides. You are not paying for work that has not happened yet. The builder gets paid promptly when they hit each stage. Nobody is out of pocket for long, and both sides have an incentive to keep the project moving.

A good builder will welcome a clear payment schedule. It protects them too — they get paid at defined points, which is better than chasing a lump sum at the end.

How much deposit is reasonable?

A deposit of 10-15% of the total contract value is standard for most domestic building work. This covers the builder reserving time in their diary, initial material orders, and site setup.

A higher deposit — up to 25% — can be reasonable if the builder needs to order expensive materials upfront. Bespoke kitchen units, structural steelwork, or specialist tiles often need to be paid for before they are delivered. In that case, the builder should explain exactly what the deposit covers.

Red flags on deposits:

• A builder who asks for 50% or more before any work starts
• A builder who will not provide a written breakdown of what the deposit covers
• A builder who wants cash only and will not give a receipt
• A builder who pressures you to pay quickly "before the price goes up"

A professional builder understands that trust works both ways. They should be happy to explain their payment structure and put it in writing.

Stage payment guide: single-storey extension

A single-storey rear or side extension is the most common domestic building project. Here is a typical payment breakdown:

Stage 1: Deposit (10%)

Paid on signing the contract. Covers diary reservation, initial material orders, and site setup (skip hire, scaffolding arrangement).

Stage 2: Foundations complete (20%)

The footings are dug, the concrete is poured, and the foundations have been signed off by Building Control. This is a significant milestone — it means the builder has committed equipment and labour to your project.

Stage 3: Walls to wall plate level (20%)

The blockwork or brickwork is up to the point where the roof structure will sit. The extension is taking shape. Lintels are in, and any structural steelwork is installed.

Stage 4: Roof complete and watertight (20%)

The roof structure is on, the tiles or membrane are laid, and the extension is weathertight. This is a major milestone because the building is now protected from the elements and internal work can begin.

Stage 5: First fix complete (15%)

All the behind-the-wall work is done: plumbing roughed in, electrics cabled, plasterboard up, plastering complete. This stage is less visible than the structural work, but it represents a significant amount of skilled labour.

Stage 6: Second fix and completion (10%)

Final finishes: kitchen or bathroom units fitted, sockets and switches installed, doors hung, painting and decorating complete. The extension is ready to use.

Stage 7: Retention (5%)

Held back for 30-90 days after practical completion. Released once all snagging items (minor defects, touch-ups, adjustments) have been completed to your satisfaction.

Stage payment guide: loft conversion

Loft conversions follow a slightly different pattern because structural steel often needs to be ordered and installed early. The steelwork is typically the single most expensive material cost, and it needs to be fabricated and delivered before the main build can start.

Deposit (10%)

Covers steel order and initial materials. Structural steel alone can cost £2,000-£5,000 depending on the span and complexity. Your builder may need to pay the steel fabricator upfront, which is why this deposit is important. They should be able to show you the steel order or invoice if you ask.

Steelwork and structural alterations (25%)

The steel beams are in, the floor is strengthened, and the structural work is complete. This is the most disruptive phase and involves the highest-value materials. Building Control will need to inspect the steelwork before the build can continue — make sure your builder has arranged this before you sign off on this stage.

Dormer or roof alterations complete (20%)

If the conversion includes a dormer, it is built and weathertight. The roof is tiled or clad. The loft space is enclosed. At this point, the major structural risk is behind you — the building is weathertight and the internal fit-out can begin.

First fix (20%)

Staircase installed, plumbing and electrics roughed in, insulation fitted, plasterboard up, plastering done. The staircase is a significant milestone — it connects the new space to the rest of the house and makes the loft feel like a real room rather than a building site.

Second fix and completion (20%)

Bathroom fitted (if en-suite), electrics finished, flooring laid, decoration complete. Final Building Control sign-off should happen at or shortly after this stage.

Retention (5%)

Held back until snagging is complete. Common snagging items on loft conversions include staircase finishing, skirting boards, paint touch-ups around Velux windows, and any issues where the new build meets the existing house.

Stage payment guide: kitchen

Kitchen projects are faster but still benefit from staged payments.

Deposit (15%)

Covers kitchen unit order (units often need to be paid for weeks before delivery). A higher deposit is reasonable here because the material cost is a large proportion of the total.

Strip-out and preparation complete (20%)

Old kitchen removed, walls prepared, any structural work done (removing a wall, fitting a beam).

Plumbing and electrics roughed in (20%)

First fix plumbing and electrics are in place, ready for the units to go in.

Units and worktops installed (30%)

The kitchen units are fitted, worktops templated and installed, and the kitchen is taking shape.

Completion and snagging (15%)

Tiling, splashbacks, appliances connected, final decoration, and snagging. This payment includes a small retention element.

Stage payment guide: bathroom

Bathrooms are typically the smallest of these projects, but the same principles apply.

Deposit (15%)

Covers ordering bathroom suite, tiles, and specialist materials.

Strip-out and plumbing roughed in (25%)

Old bathroom removed, plumbing repositioned if needed, any structural changes made.

Tiling complete (30%)

Walls and floors tiled, waterproofing done. This is the most labour-intensive part of a bathroom refit.

Fixtures fitted and completion (25%)

Bathroom suite installed, glass shower screen fitted, accessories mounted, grouting finished. Includes a small retention element.

Snagging (5%)

Held back for any final adjustments — silicone touch-ups, grout repairs, fixture adjustments.

What if my builder wants a different payment schedule?

These are guidelines, not rigid rules. Every project is slightly different, and experienced builders may have their own preferred schedule. That is fine — the important thing is that both sides agree the schedule in writing before work starts.

Questions to ask if a builder proposes a different schedule:

• What milestone does each payment correspond to?
• Why is the deposit higher than 15%? (There should be a specific reason, like material costs.)
• Is there a retention element? (There should be.)
• What happens if a milestone is delayed — does the payment date move too?

A builder who can clearly explain their payment schedule and put it in writing is someone who runs their business properly. A builder who cannot explain it, or who gets defensive when you ask, is someone to be cautious about.

"My builder wants 50% upfront"

This is one of the most searched questions homeowners ask — and for good reason. A builder who wants half the money before any work is visible is asking you to take a significant risk.

There are very few situations where 50% upfront is justified. If the builder needs to order extremely expensive materials (a £15,000 bespoke kitchen on a £30,000 project, for example), a higher deposit may be reasonable. But they should be able to show you the material invoices.

In most cases, a request for 50% or more upfront is a warning sign. It may mean the builder has cash flow problems (they need your money to finish someone else's job), or worse, they may not be planning to come back.

If a builder insists on 50% upfront and will not discuss alternatives, find a different builder.

Retention: the final piece

Retention is a small percentage (typically 2.5-5%) held back from the final payment until all snagging items are completed. Snagging includes minor defects, touch-ups, and adjustments that are noticed after the main work is finished.

Retention gives the builder an incentive to come back and finish the small things. Without it, the priority often shifts to the next job once the big money has landed. That is human nature, not bad intent — but retention solves the problem.

Retention should be released within 30-90 days of practical completion, once all snagging items on the agreed list have been resolved. Do not hold it indefinitely — that is not fair to your builder. For a full explanation, see our article on what retention money is and how it works.

Put it in writing

Whatever payment schedule you agree, put it in the contract. A verbal agreement on payment terms is a recipe for a dispute later. The contract should clearly state each milestone, the percentage or amount due at each stage, and any retention terms.

This protects you, and it protects your builder. Both sides know exactly when each payment is due, what it is for, and what happens if there is a delay. For more on why putting agreements in writing matters, see our article on whether WhatsApp agreements are legally binding and our guide on the difference between quotes and estimates.

The best builders do not wing their payment terms — they agree them in writing before work starts. If your builder sends you a TradeContract to sign, it means they take your project seriously. Learn more about TradeContract.

Are you a tradesperson?

If you are a builder, plumber, or any other trade reading this — a clear payment schedule protects you as much as it protects your customer. You get paid at defined milestones instead of chasing a lump sum at the end. You never carry more than one stage of unpaid work. And if a customer refuses to pay at any stage, you can stop work without having done thousands of pounds of free labour.

TradeContract builds the payment schedule right into the agreement. Both sides know exactly when each payment is due. Try it free at TradeContract.