Arrears vs advance self-build mortgages explained
Self-build mortgages release funds in stages tied to construction milestones — typically: land purchase, foundations, walls to plate, roof watertight, first fix, second fix and completion. Under an arrears model, the lender values the partially completed structure at each stage and releases that stage's funds after the work is done. This requires the borrower to fund each stage from cash or short-term credit, then claim reimbursement. Under an advance model, the lender releases funds at the start of each stage based on the contractor's valuation or surveyor sign-off. Advance is the only viable route for borrowers without £100k+ working capital — it adds typically 0.25–0.4 percent to the rate. Buildstore Mortgage Services originated the advance product and remains the dominant broker, working with Mansfield Building Society, Hanley Economic, Loughborough, Furness and several others.
Lender criteria for London self-build in 2026
London self-build lenders apply tighter criteria than mainstream residential lending. Typical 2026 requirements: detailed planning permission in place (outline planning is not enough), JCT or NHBC-aligned contract with a registered contractor, fixed-price build cost or contingency of 10–15 percent, structural warranty in place at start of works (NHBC, Premier Guarantee, LABC Warranty, Build-Zone, BLP Insurance, or Protek), professional consultant certificate (PCC) from a chartered architect or surveyor in lieu of warranty for some lenders, contingency cash reserves of 10–15 percent of build cost, and proof of income supporting full-build affordability. Maximum LTC (loan-to-cost) of 75–85 percent on land plus build, with maximum LTV (loan-to-value) of 65–75 percent on the completed home. London land values often constrain the LTC test before the LTV test bites — a £700k land plot with a £700k build budget needs ~£250k cash deposit to clear most lenders' LTC ceilings.
Self-build mortgage rates and fees in 2026
2026 self-build rates in London sit at 5.7–7.2 percent for a 5-year fixed product (compared to 4.5–5.4 percent for equivalent standard residential mortgages). Variable-rate self-build products are available at 6.0–7.5 percent linked to Bank of England base rate. Arrangement fees are 1.0–1.75 percent of the loan amount, plus £200–£400 valuation fee per stage drawdown (typically 6 stages, so £1,200–£2,400 of staged valuation fees). Broker fees of £1,500–£3,000 are common because the products are intermediary-only. On completion, most borrowers refinance to a mainstream residential product within 6–12 months to drop the rate by 1.0–1.8 percent — early repayment charges on self-build products are typically waived during the 6-month post-completion window for exactly this purpose.
Cash flow strategies and the role of bridging finance
Even with an advance-stage self-build mortgage, most London self-builders use bridging finance to smooth cash flow between stages. Typical bridge use cases: (1) initial land purchase where the self-build lender requires planning permission before they fund — bridge buys the land, planning is then obtained, self-build mortgage refinances the bridge; (2) gap funding between drawdowns where contractors require monthly progress payments but lender drawdowns happen every 6–10 weeks; (3) end-of-build top-up to fund snagging and landscaping while waiting for final valuation. Bridging rates in 2026 are 0.65–1.1 percent per month for prime London property, with 1–2 percent arrangement fees. A typical London self-build uses £150k–£400k of bridging at peak. Always model cash flow weekly through the build, not monthly, because contractor cashflow demands rarely align with stage drawdowns.
