Chapter 3 of 10 · Rates, lenders and switching · 1 of 10
A mortgage top-up in Ireland: borrowing for an extension or a retrofit
Checked 21 Oct 2026the Central Bank's mortgage measures, Revenue's rules and the scheme operators' published terms.
Topping up your mortgage for an extension or retrofit: lender rules, green top-ups, valuations and how it compares with a personal loan.
Check before you hire: a architect should be on the register kept by the RIAI. RIAI: register of architects
Written in plain English for the person buying, selling or switching. This guide covers the Republic of Ireland only.
A top-up is extra money borrowed from your mortgage lender, secured on your home, usually to pay for an extension, a renovation or an energy upgrade. It is the most common way to fund building work on a home you already own. This guide explains how a top-up works, what the lender checks, the green top-ups for retrofits, and how a top-up compares with a personal loan.
What a top-up is
A top-up is a second loan from your mortgage lender, held in its own account beside your existing mortgage. It has its own rate, its own term and its own monthly payment. The lender secures it on your home, like the first loan. See the glossary for terms.
Your existing mortgage does not change. If you hold a tracker, a top-up lets you keep it on the old balance and borrow the extra at a new rate. Our tracker guide explains why that matters.
What the lender checks
Three things decide whether you get a top-up and how much.
The value of your home
The lender sends a valuer (with a PSRA licence) to put a figure on your home, and in some cases on its value after the works. The fee is about €185. See what a valuer does. The Central Bank's limit of 90% of value applies to your whole borrowing, old loan plus top-up. Most lenders set their own limit below that for a top-up.
Your income and spending
The lender runs the same tests as for a new mortgage: your income, your outgoings, a stress test at a higher rate, and your age at the end of the term. A top-up for building work is new lending, so the lender looks at the Central Bank's income multiples as well as its own rules. Switching and restructuring are outside those limits, but extra borrowing is not. Our guide on the Central Bank rules sets them out.
The works
The lender wants to know what the money is for. It usually asks for:
- A description of the works and a plan or drawings.
- Quotes from builders, or a cost estimate from an architect (on the RIAI register) or an engineer or building surveyor (Engineers Ireland or the SCSI). See what an architect does.
- Planning permission, or a note that the works are exempt.
- For a large build, release of the money in stages as the work is certified.
A worked example
Say you want to borrow €40,000 for an extension. Your lender offers the top-up at 3.5% fixed. The table shows the cost over three terms, from our repayment calculator.
| Term | Monthly payment | Total interest |
|---|---|---|
| 10 years | €396 | About €7,470 |
| 15 years | €286 | About €11,460 |
| 20 years | €232 | About €15,680 |
A longer term costs less each month and more in total. Most lenders let you pick a term up to the end of your existing mortgage, and some allow longer. The rate is the lender's rate for the top-up, which can differ from the rate on your main loan.
A top-up against a personal loan
A personal loan is unsecured, which means the lender has no claim on your home. The rate is higher and the term is shorter, usually 1 to 7 years. Personal loan rates are not on this site; the CCPC's comparison tool lists them.
To show the shape of the comparison, take the same €40,000 with a personal loan at 7% over 5 years. That rate is an illustration, not a quote.
| Top-up at 3.5% over 20 years | Personal loan at 7% over 5 years | |
|---|---|---|
| Monthly payment | €232 | €792 |
| Total interest | About €15,680 | About €7,530 |
| Secured on your home | Yes | No |
| Valuation and lender's checks | Yes | Fewer |
The top-up costs less each month and twice as much in total, because it runs four times as long. The personal loan costs more each month and less in total, and does not put your home at risk. A top-up over 5 years at 3.5% would cost about €3,670 in interest, less than either.
The honest comparison is at the same term. If you can afford the higher payment, a shorter term on either loan saves the most interest.
Green top-ups
Some lenders offer a green top-up: borrowing at a lower rate for works that cut the home's energy use. In the lenders' published terms in October 2026, four of the ten lenders on our pages offer one. The usual works are insulation, windows and doors, a heat pump, and solar panels.
The lender typically asks for:
- A BER (a Building Energy Rating) before the works, from a BER assessor (on SEAI's register). See what a BER assessor does.
- A plan showing the works bring the home to a set rating, often B3 or better, or that the works are on SEAI's grant list.
- A new BER after the works, in some cases, to keep the rate.
Our green mortgage guide covers the ratings and the rates.
SEAI grants first
SEAI pays grants for the same works: attic and wall insulation, heat pumps, solar panels, windows and doors. The grant reduces what you borrow. Apply for the grant before the works start, as SEAI does not pay for work already done. The One Stop Shop route handles the grant and the works together for a deep retrofit. SEAI's page lists the amounts.
Planning permission
An extension at the rear of a house of up to 40 square metres is usually exempt from planning permission, as long as the conditions on height, garden space and earlier extensions are met. Anything larger, or to the front or side, needs permission. The lender asks for the permission or for a note from your architect that the works are exempt. Our guide on planning permission sets out the rules.
The steps
- Get a cost for the works from an architect or a builder, with a margin for the unexpected.
- Check SEAI's grants and take them off the cost.
- Ask your lender what it offers: a standard top-up, a green top-up, and the terms for each.
- Compare the top-up against a personal loan at the same term.
- Apply with the drawings, the quotes and the planning position.
- The valuation, then the loan offer.
- The money is released, in one sum or in stages as the work is certified.
Where this leaves you
Put the amount you need into the repayment calculator at two or three terms, and see what each costs a month and in total. The self-build journey covers building work step by step, from the architect to the certificates. Get quotes from architects on the RIAI register and BER assessors on SEAI's register for the plan and the rating.
Questions people ask
What is a mortgage top-up?
A top-up is extra borrowing from your mortgage lender, secured on your home, usually for building work. It is a separate loan account at its own rate and term, alongside your existing mortgage.
How much can I top up my mortgage by?
The lender measures your whole borrowing, old loan plus top-up, against the home's value and your income. The Central Bank's 90% limit on value applies, and the lender's own affordability tests apply. The amount also depends on the cost of the works.
Is a top-up cheaper than a personal loan?
A top-up usually has a lower rate but a longer term, so it costs less each month and more in total. A personal loan has a higher rate and a shorter term. In our example, a €40,000 top-up over 20 years costs about €15,700 in interest and a 5-year personal loan about €7,500.
Do I need planning permission for a top-up?
The lender needs to know the works are lawful. An extension of up to 40 square metres at the rear is usually exempt from planning permission if it meets the conditions. Larger works need permission, and the lender asks for a copy.
What is a green top-up?
Extra mortgage borrowing at a lower rate for energy works such as insulation, windows, a heat pump or solar panels. Some lenders offer one. The lender usually asks for a BER before and after, or for the works to be on SEAI's list.