Renovating One Partner's Flat When Two People Live There

The work begins with a conversation, not a quote

A couple has been living together for three years. The flat belongs to one of them: they bought it before the relationship started, they are still paying the mortgage, and the other person contributes a monthly amount they both pompously call rent even though it is really a contribution to shared expenses. So far, more or less in order. One day, over a long lunch, someone says: we should redo the bathroom. The other replies: and while we're at it, the kitchen. And there, without anyone noticing, a financial negotiation has begun that probably won't be voiced as a negotiation.

Because a renovation is not the same as changing the sofa. Painting the walls, replacing the flooring, tiling the bathroom or swapping the kitchen units are investments that become part of the property. And the property, legally, still has a single name on the deed. That asymmetry, which everyday life hides because one and the other do the shopping, split the electricity and take turns picking up the weekend bills, reappears in all its starkness the day someone has to open their wallet for a six-thousand-euro job.

It is not a legal matter in the first instance, it is a matter of honesty. Anyone putting money into an improvement that stays in a home that isn't theirs should know, before contributing, in what form they are contributing.

What creaks in the informal model

The most common model, and the most dangerous, is the silent model: both pay halves, nobody talks about the legal side, and the couple trusts that if something breaks in the future they will sort it out like adults. It is a model based on optimism, not on logic.

The first crack appears with the simple passage of time. If after five years the new kitchen has cost nine thousand euros and the couple separates, that kitchen doesn't get uninstalled. It stays. The investment has been amortised in a home that legally still belongs to the owner, and the non-owner has financed part of someone else's asset. The second crack, even before any separation, is emotional in nature: the non-owner starts to feel they don't make decisions about the flat because it isn't theirs, and at the same time they are paying as if it were. That dissonance turns into small fights (the choice of wall colour, the brand of oven) that are really echoes of the big unspoken fight.

The only way to avoid the wear and tear is to put a name to the legal arrangement before signing the first quote. There are three reasonable options, and it is worth knowing them so you can choose the one that fits the couple's stage, not to avoid choosing.

1. The contribution is treated as a documented loan

One pays, the other appears as borrower for their corresponding share, and a private loan contract is signed with a repayment schedule. It sounds cold, and it is, but it is the option that protects the non-owner. If the relationship ends, the loan is cancelled with repayment; if the relationship lasts a lifetime, the loan is paid off calmly. The taxation of a private loan in Spain requires declaring the transaction and applying an interest rate at least equal to the legal rate of money, but the tax cost is manageable and the legal security is high.

Made-up numerical example: the bathroom renovation costs 7,200 euros. The couple decides the flat's owner puts in 4,000 and the other 3,200 as a five-year loan. The monthly instalment is around 55 euros, and the day the relationship ends (whether through separation or a formalised marriage) there is a clean balance to cancel.

2. The contribution is treated as a conscious gift

The non-owner gives the money away. Full stop. They know that money stays in a home that isn't theirs and accept it as part of the cost of living together. It is the most honest option when the couple has a very long-term view and considers the difference in ownership residual compared to the shared project. It has its legal form, the gift between private individuals, its tax implications (inheritance and gift tax, which varies a lot by region) and its zero emotional cost if everything goes well. But it is the most vulnerable option if things go wrong, and it is worth knowing that beforehand, not afterwards.

3. The contribution is treated as a claim on future capital gains

This is the most sophisticated formula and the least common. The two people sign a private agreement in which they acknowledge that the non-owner's contribution will be returned, adjusted, the day the flat is sold, whether or not that coincides with a separation. If the flat was bought for 220,000 and sold fifteen years later for 310,000, the adjustment can apply the percentage of the capital gain to the initial investment. It is the closest thing to a startup's sweat equity: you work (or contribute) in exchange for a future stake in the asset you help build.

The secondary problem nobody sees

Beyond the chosen model, there is an operational problem couples tend to underestimate: documenting the process. The plumber's invoice, the delivery note from the tile supplier, the transfer that covered the painter's labour. If in three or seven years the need arises to prove who paid what, and there is no record, the conversation turns into a duel of memories. Each renovation expense should be logged with its date, amount, supplier and proportion of contribution. Not out of distrust, out of hygiene. The same way you sign a rental contract even though you like the person.

And then there is another layer: when the renovation overlaps with the flat's everyday expenses (electricity, water, building charges, minor repairs), everything tends to blur into a single confusing set of accounts. It is worth keeping the renovation in an isolated category, separate from the monthly flow, precisely so that when the time comes to settle accounts (or, hopefully, not to have to settle them) the numbers are clean.

How to close it without making it a taboo subject

The first thing is to talk it through calmly, away from the excitement of the renovation idea. The second is to choose the arrangement: loan, gift, capital gains or any reasonable hybrid. The third is to document: every euro contributed must be traced to its category. This is where an expense-sharing tool designed for couples adds real value, not just for the day-to-day but for recording extraordinary expenses with a contribution perimeter different from the normal one. Any decent system should let you create separate categories, different splitting proportions and export the history to the cent. ControlarGastos does exactly that, and that frees the couple from arguing about figures: all that's left to discuss is which category applies.

Conclusion: the renovation as a maturity test

Renovating one partner's flat when two people live there is, in reality, a maturity test for the shared project. Not because you need to sign contracts to love someone, but because signing a contract is the only way to stop thinking about the contract. Once it is clear what is a loan, what is a gift and what is a contribution to shared enjoyment, the couple can choose the wall colour without the conversation dragging financial tension along underneath. What destroys long-term projects is not money, it is ambiguity. And ambiguity, in a renovation, is exactly what you can least afford.