How to Finance Your Home Extension or Loft Conversion
A practical guide to your options — remortgage, further advance, personal loan, second charge, and more. Written from the perspective of a contractor who's seen what works and what doesn't.
📌 Rule #1: Get a realistic estimate before speaking to a lender — lenders need a clear project scope and a credible figure. Use our cost calculator or book a free survey.
Your Finance Options — Explained
The right route depends on your equity, current mortgage situation, project size, and timeline. Here's what each option means in practice.
Remortgage
Most popularRemortgage to a higher loan amount using your existing equity, releasing cash to fund the build.
✅ Pros
- +Usually the cheapest rate (2–5% typical)
- +Large sums available (£50k–£250k+)
- +Interest spread over mortgage term
⚠️ Cons
- –Early repayment charges may apply on current deal
- –Requires equity (typically 75–80% LTV max)
- –Takes 4–12 weeks to complete
Best for
Projects over £40,000 where you have at least 25% equity in the property
💡 RCB tip
Get your project estimate from RCB first — lenders want a clear figure and scope before agreeing to the additional borrowing.
Further Advance
Low frictionBorrow additional funds from your existing mortgage lender without switching products.
✅ Pros
- +No product switch — simpler process
- +Single lender relationship
- +Usually faster than full remortgage
⚠️ Cons
- –Limited to your current lender's rates
- –Not always competitive vs market remortgage
- –Must meet lender's affordability criteria
Best for
Clients happy with their current lender and deal, or in a fixed-rate period with high ERCs
💡 RCB tip
Ask your current lender for a further advance illustration before assuming you need to remortgage.
Personal / Home Improvement Loan
Fast to arrangeUnsecured personal loan or a secured home improvement loan for smaller to mid-range projects.
✅ Pros
- +No remortgage required
- +Available up to £25,000–£50,000 unsecured
- +Can complete in days vs weeks for mortgage products
⚠️ Cons
- –Higher interest rates (5–15%+ typical unsecured)
- –Shorter repayment term increases monthly cost
- –Not suitable for large-scale projects
Best for
Projects under £30,000 where remortgaging is not viable or practical
💡 RCB tip
Compare credit union rates and high-street bank home improvement products before using a comparison site.
Second Charge Mortgage
Keep your current dealA second mortgage secured against your property, sitting behind your first charge lender.
✅ Pros
- +Keeps your first mortgage rate intact
- +Can release substantial equity
- +Suitable if high ERCs make remortgage expensive
⚠️ Cons
- –Higher interest rates than first charge
- –Two mortgage payments
- –Specialist product — needs a broker
Best for
Clients locked into a competitive first mortgage with high ERCs who still need £20k–£100k+
💡 RCB tip
Always use an independent mortgage broker for second charge products — rates and lender criteria vary widely.
Equity Release (Lifetime Mortgage)
For 55+ homeownersRelease equity from your home without monthly repayments — interest rolls up and is repaid on sale or death.
✅ Pros
- +No monthly repayments required
- +Available to homeowners aged 55+
- +Can fund large projects with no income test
⚠️ Cons
- –Reduces estate value (compound interest)
- –Early repayment charges are typically severe
- –Specialist legal advice required
Best for
Older homeowners with significant equity who want to fund improvements without monthly payments
💡 RCB tip
Always take independent financial and legal advice from an equity release specialist before proceeding.
Self-Build / Green Mortgage Products
Eco projectsSpecialist mortgage products for energy-efficiency improvements, available from an increasing number of lenders.
✅ Pros
- +Lower rates for qualifying green improvements
- +Government incentives may stack on top
- +Available for new loft/extension + retrofit
⚠️ Cons
- –Limited lender availability
- –Requires qualifying improvements (EPC uplift)
- –Can be slow to arrange
Best for
Extensions or refurbishments that meaningfully improve your property's EPC rating
💡 RCB tip
Pair with the Boiler Upgrade Scheme (£7,500 for heat pumps) or a Heat Network Grant where applicable.
The Right Order of Events
Getting the sequence right saves time and protects you. Here's what experienced clients do.
Get a realistic estimate first
Before speaking to any lender, get a detailed estimate from a reputable contractor. Lenders want to see a clear project scope and a credible figure — a ballpark alone is rarely enough.
Choose your finance route
Assess which option suits your situation — equity available, current mortgage deal, project size, and timeline. An independent mortgage broker can model the options side by side.
Get a Decision in Principle (DIP)
For remortgage or further advance routes, a DIP confirms the lender's appetite before you commit to a build start date. Most lenders will require a full valuation of the property.
Align finance drawdown with your build stages
Understand how and when you'll release funds. Many contractors work in milestone-based stage payments — make sure your finance is available when each stage falls due.
Set a realistic contingency
Always budget 10–15% above your estimate. Structural surprises, soil conditions, and scope changes are common — and you don't want finance to run short mid-project.
Sign the contract and start the build
Once finance is confirmed, a reputable contractor will issue a contract with a payment schedule. RCB's contracts always include a defined stage-payment structure so you can match it to your drawdown plan.
Finance FAQs
How long does it take to arrange finance for an extension?
A personal loan can be arranged in days. A remortgage or further advance typically takes 4–12 weeks, including valuation and conveyancing. Factor this into your project start date.
Will my lender need to know about the building work?
Yes — if you're remortgaging or taking a further advance, the lender will value the property and will want to know the project scope. For personal loans, no mortgage notification is usually required, but always check your mortgage terms.
Can I start building before the finance completes?
Not advisable. Confirm your finance before committing to a build start date or signing a contract. Starting without confirmed funds is a significant risk to both you and your contractor.
Does planning permission affect my ability to get finance?
Yes — some lenders require confirmed planning or Permitted Development status before agreeing to fund a project. RCB can help confirm your planning position before you approach lenders.
What happens if the build costs more than expected?
This is why a 10–15% contingency is essential. If costs exceed your original finance amount, you'll need to arrange additional funds. Detailed scoping and a fixed-price contract reduce the risk of unexpected overruns.
Ready to Get a Proper Estimate?
Lenders need a real figure. Book a free survey with RCB — we'll measure up, assess the scope, and give you a detailed estimate you can take to your mortgage adviser.