Self-build mortgage for a barn conversion

Costs verified against BCIS Online (May 2026 release) and ONS Construction Output Price Index, April 2026. Class Q rules current to the 21 May 2025 GPDO amendment.

Barn conversion finance is a niche of the self-build mortgage market. Ecology Building Society, several regional building societies and Buildstore-introduced lenders cover the bulk of barn cases. LTV is typically capped at 75% of end value or 80% of cost.

Arrears vs advance

Arrears. Funds released after each stage is independently valued. You bridge the cash for each stage. Typical for new-build self-build.
Advance. Funds released at the start of each stage. Better cashflow for barn conversion where stages have lumpy spend (re-roof, M&E first fix, kitchen).

Documentation

Lenders require detailed plans, a costs schedule signed by a chartered surveyor, programme, contractor warranty (typically 10-year Premier Guarantee or LABC) and proof of planning consent. Class Q approval counts as planning consent for this purpose.

Typical rates

Self-build rates run 1.5 to 2.5 percentage points above mainstream residential. Arrangement fees £1,500-£3,000. Buildstore aggregates the market; BSA lists building-society members.

Sources cited on this page