Self-Build Mortgages: How Funding Works at Every Stage

How self-build and custom-build mortgages release funds across the build; arrears versus advance stage payments, land and deposit planning, and what lenders need at each stage.

A client called us last spring, three weeks into their self-build, to ask why their bank account had gone from comfortable to empty. They had assumed the mortgage funds would arrive before they needed to pay the groundworks contractor. Their lender operated on an arrear’s basis. The contractor needed paying before the stage was signed off. Nobody had explained the gap.

That gap is the single most common reason self-builds run into difficulty in the early stages, and it is entirely avoidable with the right preparation. Self-build mortgages work differently from any other mortgage product in the market, and understanding those differences before you put a spade in the ground makes the difference between a project that flows and one that stalls.

This guide explains how self-build and custom-build mortgages release funds, what lenders need to see at each stage, and how to plan your finances so the cashflow gap never becomes a crisis.

What is a self-build mortgage and how does it differ from a standard mortgage?

A standard mortgage releases a single lump sum on completion of a property purchase. A self-build mortgage releases funds in stages, timed to match specific milestones in the construction process. Rather than receiving the full amount upfront, you draw down tranches of the loan as the build progresses, with a surveyor appointed by the lender visiting the site to confirm each stage is complete before the next payment is released.

This staged structure exists because the lender is taking on a different kind of risk. At the point of application, there is no finished property to secure the loan against, only a plot of land and a set of plans. The stage payment mechanism lets the lender control its exposure throughout the process, releasing money only once value has demonstrably been added.

The interest structure is also different. During the build phase, you typically pay interest only on the funds that have been drawn down, not on the full loan amount. So, if your total mortgage is £400,000 but only £80,000 has been released after the first stage, you pay interest on £80,000. Payments rise as each further tranche is drawn. Once the build is complete and the full sum is released, the mortgage converts to a standard repayment basis, at which point most borrowers remortgage onto a conventional residential product at a more competitive rate.

The lender pool is smaller than for standard mortgages. Around 26 providers currently offer self-build products in the UK, the majority of which are building societies rather than high street banks. Specialist intermediary services such as BuildStore and BuildLoan work exclusively with self-build lenders and have access to products not available direct to the public.

Stage payments: arrears versus advance, and why it matters for cashflow

Every self-build lender operates one of two payment models, and the distinction between them has more practical impact than almost any other feature of the mortgage.

Arrears stage payments are the more common arrangement. Funds are released after each construction stage has been completed and signed off by the lender’s surveyor. This means you pay for materials and labour out of your own cash, and the mortgage then reimburses you once the stage is verified. The lender’s risk is lower, which is why arrears products typically carry slightly better interest rates. The trade-off is that you need meaningful cash reserves to bridge each stage.

Advance stage payments release funds before the stage begins. You receive the agreed drawdown at the start of each phase, which you use to pay contractors and purchase materials. This is the structure that removes the cashflow gap described above. Fewer lenders offer advance products and rates are usually modestly higher, but for borrowers who do not have large reserves sitting in cash, the advance model is often the only practical option.

The typical stages at which funds are released are broadly consistent across lenders, though the exact percentages and number of tranches vary:

Build Stage	Milestone
Foundations	Groundwork and foundations complete
Wall plate level	External walls built to eaves height
Wind and watertight	Roof on, windows and external doors fitted
First fix	Internal framework, wiring and plumbing rough-in
Second fix and completion	Plastering, joinery, fixtures and fittings, final certificate

On a £400,000 total mortgage across five stages, the arrears model means you need to find perhaps £60,000 to £80,000 per stage from your own resources before the lender reimburses you. If you have that liquidity, arrears works well and costs you less. If you do not, advance is the right structure regardless of the marginal rate difference.

Land purchase, deposit and total cost planning

The deposit requirement for a self-build mortgage is higher than for a standard residential mortgage. Most lenders ask for a minimum of 25% of the total project cost, defined as land plus build, and some require up to 40% or 50% depending on the complexity of the build and the LTV relative to the anticipated end value of the finished home.

If you already own the land, its current market value counts towards the deposit. This is a significant advantage that many clients do not realise when they first approach us. A plot valued at £150,000 on a £500,000 total project represents a 30% deposit before you have put any additional cash in. Lenders will instruct an independent valuation of the plot, and the figure they use is that surveyed value rather than what you paid for it, which can work in your favour if you bought the land some years ago.

The key numbers to build your budget around:

Cost element	Typical range / guidance
Land cost	30 to 50% of finished home value (varies significantly by region)
Build cost per sq metre	£2,300 to £3,600+ depending on specification (Source: MyBuildAlly / Livedin, 2026)
Professional fees	10 to 15% on top of the build contract sum
Contingency fund	Minimum 15%, recommended 20% of total build cost
VAT reclaim	Available on materials via HMRC DIY Housebuilders Scheme (VAT431NB)

A note on VAT: self-builders who will occupy the finished home as their primary residence can reclaim the VAT paid on eligible materials via HMRC’s DIY Housebuilders Scheme (form VAT431NB). Labour on a new build carried out by a VAT-registered builder is zero-rated so VAT does not arise on the construction contract itself. The materials reclaim can amount to several thousand pounds and must be submitted within six months of completion. You can only make one claim, so keeping meticulous receipts throughout the build matters.

Self-build versus custom build: understanding the difference

The terms are often used interchangeably, but they describe distinct routes to building your own home.

A self-build is a project where you directly commission and manage the construction of a home on land you own or are purchasing. You appoint the architect, obtain planning permission, engage a contractor or manage subcontractors yourself, and take full responsibility for the build programme. It offers the most control and typically the highest scope for personalisation.

A custom build sits closer to the developer model. A developer or enabler company prepares a serviced plot, connects utilities and obtains the planning framework. You then commission your home to be built to your specification within that framework. The developer manages much of the infrastructure, and some custom build schemes offer plots with a permitted design envelope. Hinckley and Rugby Building Society, for example, has a dedicated custom build mortgage product available via BuildLoan, with rates from 4.74% on a three-year discount and borrowing available to 90% of total project cost.

For clients more comfortable with a structured process and fewer moving parts, custom build is often the more manageable route. For those who want full control from the ground up, self-build delivers that, with a correspondingly more intensive management requirement.

What lenders need at each stage

Lender requirements at application are more extensive than for a standard mortgage, and it pays to have everything assembled before approaching a lender. A well-packaged application moves considerably faster than one assembled piecemeal.

At application stage, you will typically need: full planning permission (outline permission can be acceptable on some products, but full permission significantly strengthens the case), detailed architectural drawings, a costed schedule of works from your builder or quantity surveyor, confirmation of site insurance arrangements, evidence of a structural warranty in place or arranged, and your usual income and credit documentation.

Income assessment for self-build follows the same affordability principles as for any mortgage, but with one important additional dimension. Lenders assess whether you can service the interest payments during the build phase on top of any current housing costs such as rent or an existing mortgage. For clients with complex income, whether that is as a company director drawing salary and dividends, a self-employed professional with variable earnings, or a foreign national with income denominated in another currency, the lender selection matters considerably. Mainstream lenders who offer self-build products often have conservative income assessment models. The specialist building societies tend to apply more considered underwriting and will look at a fuller picture of your finances.

During the build, your lender will instruct a surveyor to inspect and sign off each stage before releasing the next tranche. The documentation required at each stage inspection is usually straightforward: evidence of the works completed and confirmation from your architect or main contractor that the stage is finished. Stage inspections are typically managed within a few working days, though it pays to give the lender advance notice before you expect to reach each milestone.

A short case study

A client approached us with a plot in Surrey that she had purchased outright two years earlier for £220,000. She was a company director with a combination of salary and dividends and wanted to build a four-bedroom detached home to a high specification. Total project cost was budgeted at £760,000 including land, build, professional fees and contingency.

With the land already owned, the £220,000 equity represented 29% of the total project cost before she contributed any further cash. We sourced a specialist self-build mortgage at 85% of projected end value, structured on an advance basis given that her day-to-day cash reserves were tied up in the business. The advance model meant funds were available at the start of each stage, which her main contractor was comfortable with.

The finished home was valued at £1.1 million on completion. She remortgaged at that point onto a five-year fixed rate at 65% LTV. The combination of land she had already owned, the advance stage payment structure, and the ability to present her director income correctly meant she built a home worth considerably more than the all-in cost of delivery.

Frequently Asked Questions

Nothing in this article constitutes financial or legal advice. Mortgage eligibility depends on individual circumstances. Always speak to a qualified specialist before proceeding.

Planning a self-build and want to understand how the finance works for your situation?  Speak to a London FS adviser