Planning Your Own Grand Design? Get a Mortgage to Fund a Self-Build or Home Extension
Guest author: Aaron Strutt, Product and Communications Director, Trinity Financial
Estimated reading time: 7 minutes
Whether you are planning a kitchen extension, loft conversion, basement excavation, barn conversion, eco-home or a complete knockdown and rebuild, arranging the right finance is essential. In this guest article, Aaron Strutt of Trinity Financial sets out the options, from remortgaging and further advances through to specialist self-build mortgages and staged drawdown.
What has been happening to mortgage rates?
Rates, lender names and product terms in this section were correct at time of publication, August 2026, and are subject to change.
The mortgage pricing merry-go-round has continued over the last few weeks with banks and building societies raising the cost of their fixed and tracker-rate deals after a prolonged period of making their mortgages more competitively priced. The mortgage hikes resumed after the bombing in Iran started again and problems intensified in the Strait of Hormuz pushing up borrowing costs.
Despite the recent increases, Trinity Financial's brokers still have access to competitive two and five-year fixed-rate mortgages starting from around 4.6% and tracker rates from 3.99%. Lloyds Banking Group has started to push its cheap mortgages available to new and existing Lloyds Premier current account holders earning £100,000 or more as part of the announcement that the Halifax brand is going to be retired after 173 years.
As an incentive to open their current account, Lloyds typically issues rates 0.2% lower than the standard Halifax mortgages, meaning higher earners can often get access to the best mortgage rates in the market and they currently start from just over 4.45%. HSBC and Barclays are also offering mortgage and current account incentives for higher earners which include income stretches, lower fixed rates and cheaper arrangement fees.
Can you remortgage to pay for a home extension?
Homeowners with sufficient equity may be able to remortgage and borrow additional funds for home improvements. It often makes sense to do this when your fixed, or tracker rate is due to expire, so if you need to remortgage to another bank or building society to raise the funds you need then you should not have to pay early repayment charges. Some lenders will want to see a breakdown of costs if you are doing a substantial renovation while others will not.
The amount of money you can borrow will depend on:
The value of your property
Your outstanding mortgage balance
Your income, and your credit commitments such as credit cards, loans and childcare costs
The cost and scale of the proposed work
The lender's loan-to-value limits, based on the outstanding balance and the value of the home
Income multiples, which range between four and 6.5 times single and joint salaries
For example, somebody with a property worth £750,000 and a £300,000 mortgage may be able to release some of their equity to fund an extension or major renovation.
Some lenders are more comfortable than others with capital raising for building work, particularly where the project is extensive.
If you are going to do structural work, it is worth making sure you have adequate buildings insurance in case something goes wrong.
Should you remortgage or take a further advance to pay for the work?
Remortgaging is not always the best option, especially if your current mortgage has a low fixed rate or a substantial early repayment charge. While many of the ultra-cheap mortgages have finished now, some homeowners still have time to run on their two or three per cent mortgage deals. This is not something homeowners should give up lightly.
Your options may include:
Remortgaging to a new lender
Applying for a further advance when your fixed rate finishes as part of the product transfer process, or taking a further advance or additional borrowing from your existing lender
Arranging a second-charge mortgage
Using short-term bridging or renovation finance
A good mortgage broker, like Trinity Financial, can compare the overall cost of each option, rather than focusing only on the headline interest rate. It is worth noting that if you take additional borrowing you may well have two parts to your mortgage which have different end dates. This can make refinancing more difficult.
When is a self-build mortgage required?
A specialist self-build mortgage may be needed when you are buying land, constructing a new property or carrying out work that makes the home temporarily uninhabitable.
Self-build mortgages can be used for:
New-build homes
Knockdown and rebuild projects
Barn, windmill and commercial property conversions
Major structural renovations
Eco-homes and modern glass houses
Partially completed projects requiring additional funds
While most high-street banks do not offer self-build mortgages, a number of building societies, specialist lenders and private banks operate in this market. Some private banks also offer competitive terms if you are looking for a larger self-build mortgage, typically over £1 million.
How does a self-build mortgage work?
Unlike a standard mortgage, where the money is normally released in one payment, self-build mortgage funds are usually released in stages.
These may include:
Purchasing the land
Completing the foundations
Building to wall-plate level
Making the property wind and watertight
Completing the internal work and receiving the final completion certificate
Some lenders release funds after each stage has been completed, while others can provide advance-stage payments or more flexible monthly drawdowns.
It is important to understand when the money will be available, as builders and suppliers may require payment before a lender releases the next instalment.
Get your finance agreed before building work starts
The most organised borrowers arrange their finance well before construction begins.
Lenders may request:
Full planning permission
Architect's drawings
A detailed schedule of works
A breakdown of building costs
Details of the contractor
Structural warranties
A contingency budget
The expected value of the finished property
They will also assess whether the mortgage is affordable both during construction and after the property has been completed.
Many lenders will review the local authority planning portal as part of the application process.
Can you release equity from another property?
It may be possible to remortgage another residential or buy-to-let property to help fund the work.
This can sometimes be cheaper than bridging or development finance, although the lender must be comfortable with the reason for raising the money.
Borrowers should consider a flexible mortgage with limited early repayment charges if the property may later be sold or refinanced. Some private banks may even be able to take cross charges on multiple properties to release a sufficiently large mortgage.
What happens to the self-build mortgage when the property is complete?
Once the property has been finished and signed off by building control, it should be possible to refinance onto a standard residential mortgage.
The new mortgage could be used to:
Repay the self-build lender
Clear a bridging loan
Repay family members
Move onto a lower mortgage rate
Release further equity
The property will normally need the correct completion certificates, warranties and Land Registry details before a mainstream lender will accept it.
Are private banks suitable for larger projects?
Private banks can be worth considering for self-build mortgages of £1 million or more.
They may take a broader view of income, bonuses, investments, business profits and other assets. They can also be more comfortable with complex borrowers, unusual properties and bespoke construction projects.
Are eco self-build mortgages available?
Some lenders offer preferential mortgage rates or reduced fees for energy-efficient homes aiming for an EPC rating of A or B.
However, borrowers should check that unusual materials or construction methods will be acceptable to mortgage lenders once the property is complete.
Speak to a specialist mortgage broker
Trinity Financial's mortgage brokers have access to lenders providing finance for home extensions, major renovations, conversions, basement excavations, new-build homes and knockdown-and-rebuild projects.
We can also help borrowers who have started building work and need additional funding after costs have increased or the project has taken longer than expected.
Speaking to a broker early can help you understand how much you may be able to borrow, when the funds will be released and whether remortgaging or a specialist self-build mortgage is the most suitable option.
To discuss financing a home extension, renovation or self-build project, contact Trinity Financial's mortgage brokers.
→ Contact Trinity Financial on 020 7016 0790 or visit www.trinityfinancial.co.uk
→ Or email enquiries@trinityfinancial.co.uk
For the design, planning and delivery side of an extension, renovation or self-build:
→ Email us at info@visionanddesign.co.uk
→ Or call us on 07931910243
Your home may be repossessed if you do not keep up repayments on your mortgage. Bridging loans and some forms of development finance are not regulated by the Financial Conduct Authority.
The information contained within was correct at time of publication, August 2026, but is subject to change. It is for general information purposes and is not advice.
Guest article contributed by Trinity Financial. Published by Vision + Design, 26 August 2026.