Self Build Blog

Can I Get a Mortgage for a Self-Build Extension or Renovation?

Written by Emma Corfield | 3.3.2026

If you’re planning a major home renovation or extension, one of the first questions you’ll ask is: Can I get a mortgage to fund this?

The short answer is yes — but the type of mortgage, how it works, and how much you can borrow will depend on your project and your circumstances.

During the latest Self-Build Hour, hosted by architect Jenny Chandela of AC Architects, self-build finance specialist Tom McSherry of BuildStore explained the funding routes available to homeowners looking to extend, renovate or convert property.

Here’s what you need to know.

WHAT TYPES OF PROJECTS CAN BE FINANCED?

Specialist lenders can support a wide range of renovation and extension projects, including:

  • LIGHT REFURBISHMENTS – cosmetic upgrades or modest improvements

  • STRUCTURAL RENOVATIONS – reconfigurations, major upgrades, or bringing a property back into use

  • EXTENSIONS – single-storey, double-storey, or wraparound additions

  • CONVERSIONS – including barns, churches, or other non-standard buildings

  • UNINHABITABLE PROPERTIES – homes requiring significant work before they can be lived in

The important point is that these projects are often funded by the same specialist lenders who support self-build homes — but using products tailored to renovation.

START WITH YOUR BUDGET, NOT YOUR DESIGN

One of the strongest messages from the session was this to establish your budget before progressing with your design. It can be tempting to develop plans and then “hope” they fit in with your finances.   

However: 

  • Your budget defines what’s realistically achievable.

  • It determines the scale of your extension.

  • It affects specification and finishes.

  • It influences contingency planning.

Your full budget should include the property purchase price, construction costs, professional fees, insurances and warranties and contingency plans. For older or listed properties, a higher contingency — sometimes closer to 20% — is advisable, as hidden issues often emerge once work begins.

WHAT ARE YOUR MORTGAGE OPTIONS?

Your funding route will depend on whether you already own the property. 

 

STANDARD REMORTGAGE OR FURTHER ADVANCE

This may be suitable for light improvements or smaller extensions. However, this will come with limitations such as your borrowing is capped against the current property value and funds are usually released in one lump sum. You may also pay interest on money that you haven't yet spent. This option can work well for straightforward improvements- but its often restrictive for larger renovations.  

BRIDGING FINANCE

Bridging can be used for:

  • Purchasing un-mortgageable property

  • Short-term funding while renovating

HOWEVER:

  • It’s typically limited to 12 months (for regulated residential cases)

  • Usually capped at around 70% loan-to-value

  • It’s generally more expensive than standard mortgages

 A key risk is that property values often drop during renovation, meaning you can’t rely on increased value mid-project to release further funds. Bridging works best where there is a clear, short-term exit strategy.

 

SPECIALIST RENOVATION OR STAGE PAYMENT MORTGAGES 

For larger or more complex projects, this is often the most effective solution.

These mortgages differ significantly from standard lending:

  • You can often borrow against the end value of the property (once works are complete), not just its current value.

  • Up to 95% of construction costs may be available (subject to criteria).

  • Funds are released in stages as work progresses.

  • During construction, the mortgage may be interest-only.

  • Once complete, you typically transfer onto a standard residential product.

This structure improves cash flow and reduces the need to self-fund large portions upfront.

WHY STAGE PAYMENTS MATTER

One critical consideration in renovation finance is that your property may fall in value during construction. If your borrowing is tied to current value, that can create funding gaps. Stage payment mortgages are designed specifically to manage this risk. Instead of relying on the property’s temporary value mid-renovation, funds are released based on agreed construction stages. This can make a major difference to project viability.

WHAT ABOUT INSURANCES AND STRUCTURAL WARRANTIES?

If you are undertaking structural work, especially on:

  • Major renovations

  • Conversions

  • Projects involving significant alteration

You should strongly consider a 10-year structural warranty.

Even if you plan to stay long-term, circumstances change. If you sell within 10 years, buyers (and their lenders) will often expect a warranty in place.

Arranging this early in the project is essential — it cannot usually be added retrospectively once works are complete.

You must also ensure:

  • The property is properly insured during works

  • Vacant property rules are understood

  • Site insurance reflects the construction phase

 WHEN SHOULD YOU SPEAK TO A SPECIALIST?

The answer: as early as possible.

 

Even if:

  • You’re buying in cash

  • You haven’t found a property yet

  • You’re only exploring ideas

 

Early advice helps you:

 

  • Understand borrowing capacity

  • Set a realistic project brief

  • Assess viability before committing

  • Avoid purchasing something you cannot afford to complete

 

You may even discover you can achieve more than you initially thought.

 

KEY CHALLENGES TO BE AWARE OF 

Before proceeding, consider:

  •  Is the property currently mortgageable?

  • Will it remain habitable during works?

  • Do you need planning permission?

  • How long will the project realistically take?

  • Are you using a main contractor, project manager, or DIY approach?

  • Is your contingency sufficient?

Renovation projects are inherently less predictable than new builds. The deeper you go into an existing structure, the more unknowns can emerge.

Lenders prefer to see that you’ve planned for this.

Financing a self-build extension or renovation is absolutely possible — but it requires the right product and early, informed planning. Taking the time to plan and consider your budget and speaking to the right professionals so that you have a clear understanding of your mortgage options may be the most valuable first steps that you take.

If you would like to speak with a member of our team about designing your home, get in touch. 

 
 
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