Using a Secured Loan for Home Extensions — Costs, Rates & Tips

Why Use a Secured Loan for a Home Extension?

Home extensions are one of the most common reasons UK homeowners take out secured loans, and it's easy to see why. Extensions typically cost between £30,000 and £100,000+ depending on size and specification — amounts that are too large for most unsecured personal loans (usually capped at £25,000) but perfectly suited to secured lending.

A secured loan lets you borrow the full amount you need, spread repayments over up to 25 years to keep monthly costs manageable, and — crucially — keep your existing mortgage deal intact. This last point is particularly valuable if you're on a competitive fixed rate, since remortgaging would mean giving that up and potentially paying early repayment charges.

There's also a strong financial argument: a well-planned extension can add 10–20% to your property's value, often exceeding the cost of the work itself. This means the loan can effectively pay for itself through increased equity.

Typical Extension Costs in the UK (2026)

Understanding project costs will help you determine how much to borrow. Here are rough guides based on current UK building costs:

Single-storey rear extension (3m × 5m): £35,000–£55,000. This is the most popular type of extension — adding a larger kitchen-diner or open-plan living space. Costs vary by region, with London and the South East typically 20–30% higher than the national average.

Double-storey extension: £55,000–£95,000. Building up as well as out is more cost-effective per square metre than single-storey, as you share the foundation and roof costs across two floors.

Loft conversion: £30,000–£60,000. A dormer or hip-to-gable conversion can add a bedroom and bathroom without extending the footprint of your home. This is often the best value-for-money improvement in terms of added property value.

Garage conversion: £10,000–£25,000. Converting an existing garage into a habitable room is one of the most affordable ways to add space, though it adds less value than a purpose-built extension.

Remember to budget an additional 10–15% contingency for unexpected costs. Planning permission fees (£206 for a householder application in England), building regulations approval, and architect fees (typically 5–10% of build cost) should also be factored in.

What Rates to Expect

Secured loan rates for home improvements currently start from around 6.34% for borrowers with good credit and a low loan-to-value ratio. For a typical £50,000 loan over 15 years at 7.5%, monthly repayments would be approximately £464.

Rates depend primarily on your credit score, the combined LTV (your existing mortgage plus the new loan as a percentage of your property value), and the loan term. Keeping your combined LTV below 70% will generally access the best rates.

Compare this to alternatives: an unsecured personal loan for £25,000 might charge 6–8% but over a maximum of 5–7 years, resulting in much higher monthly payments. Credit cards could cost 20–30% APR. A further advance from your mortgage lender might offer similar rates but could mean losing your current deal and paying ERCs.

Practical Tips for Financing Your Extension

Get detailed quotes from at least three builders before deciding how much to borrow. Vague estimates lead to either under-borrowing (leaving you short mid-project) or over-borrowing (paying interest on money you don't need).

Consider whether you'll need the funds in one lump sum or in stages. Secured loans are typically paid as a single lump sum, so you'll need to manage the cash flow with your builder. Many builders work on a stage-payment basis — for example, 10% upfront, 30% at foundation stage, 30% at roof level, and 30% on completion.

If you're planning the extension under permitted development rights (no planning permission needed), your loan could complete in as little as 2–3 weeks. If you need planning permission, start that process first — there's no point paying interest on a loan while you wait for planning approval.

Think about the timing. Some borrowers apply for the loan while planning and design work is underway, so funds are available the moment the builder is ready to start. This avoids costly delays.

Will the Extension Add Value?

According to recent UK property data, a well-executed extension typically adds the following to your property value: single-storey extension: 5–10% uplift; double-storey extension: 10–15% uplift; loft conversion: 10–20% uplift; garage conversion: 5–10% uplift.

The key word is 'well-executed'. A poorly designed extension that's out of keeping with the property or the street can actually reduce value. Investing in good architectural design and quality building work pays dividends in the long term.

From a lending perspective, the added value also improves your equity position, which means your overall LTV decreases after the work is complete. This can be beneficial if you later want to remortgage or borrow further.

Getting Started

Use our secured loan calculator to see estimated monthly payments for your project budget. When you're ready, apply online for a free, no-obligation quote — our FCA-authorised brokers will search our full lender panel to find the most competitive rate for your home improvement loan.

Remember: your home is used as security for a secured loan. If you don't keep up repayments, your property may be repossessed. Always make sure the monthly payments are comfortably affordable before committing.