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Can I buy a house and build an extension?

Buying a house and building an extension

You have finally signed your mortgage and bought your house, but you can see that you may outgrow it in a few years. One option would be to extend and renovate your current property to add a bedroom or bathroom.

But beware, as always, you need to be informed before you start: renovating a house is simple as it is small-scale building work. Extending a building is quite a different matter, as it usually involves structural alterations. This will require an architect to draw up a technical project and obtain a building permit, regardless of whether your home is a flat or a detached house.

In any case, the work must always be made legal, especially if it is an extension; local councils are increasingly aware of uncontrolled population growth, they monitor illegal extensions and are equipped with more resources (drones, helicopters and satellites).

What do I need to consider when extending my property?

As we have said, it is extremely important to get information from the local council and hire an architect who will still check the urban planning regulations and certify the viability of the work, draw up the technical project and obtain the permits. It is very common that, when carrying out a renovation, people hire a builder directly, ask for a quote and carry out the renovation. And if the builder is not reputable, there is a risk that the builder will not comply with the regulations. If you have carried out an illegal renovation, you have at best carried out an extension without planning permission, but you would have obtained it if you had applied. You would only have to hire an architect to draw up the technical project of the work that you have already carried out, obtain the planning permission and make the renovation legal.

Conversely, it may be the case that the local council is already aware of this extension and it is no longer possible to make it legal. In any case you will have to pay a fine, and also demolish the extension if the local council so demands.

How much can it cost me?

In truth, it is not going to be a cheap project. Before signing your mortgage to buy your home, first of all, you will have to do the numbers: building up savings to cover the 20% that the bank will not finance, and adding other additional expenses: including the notary and land registry fees as well as taxes. You will also have to add the cost of renovating the property, for which you will have to pay the fees of the architect who will draw up the technical project. And then add the municipal building permit fee (which varies depending on the municipality and local council) and the first occupancy licence fee. In other words, it is an option that requires a lot of investment. In addition, when negotiating a larger amount of financing, the financial institution will assume a higher risk, so it will ask for more demanding conditions.

If you already own the home, another option is to apply for a mortgage loan to pay for this renovation. Compared to the option of requesting a personal loan (a good option if the budget is low, as it will normally have a limit of around €30,000), the mortgage will allow you to benefit from a lower interest rate and longer terms to make the payments (starting from a minimum of ten years), and will finance around 65% of the appraisal value. Conversely, the formalities and paperwork will be longer, and the responsibility much greater. In addition, their conditions are different to loans that also finance purchasing the property. This is a more atypical product that is not available at all banks.

When is it legal to extend?

This will depend on the urban planning regulations and the type of extension you want to carry out. If, for example, you want to create an enclosure for a terrace, patio or roof terrace, you will be modifying the appearance of the façade and it will also affect the amount of metres built. For this reason, you will need a technical project. And if you are in a residential building, you will also have to request a permit from the community of owners.

In any case, we insist that it is very important to consult the urban planning regulations. To find them out, just take a look at the website of the local council where the property is located.

If you cannot locate it, you will have to talk to a technician from the city council to clarify any doubts. In any case, you will have to obtain the following data: Firstly, the buildability, or the ratio between the square metres that can be built on a given plot (floor and ceiling).

This can sometimes be difficult to understand because the regulations provide for exceptions that do not include: storage rooms, staircases, balconies or garages. Normally, from its initial construction, the builder has taken advantage of the maximum buildable area to obtain maximum profitability, but sometimes you find that the limit has been exceeded. The setback, which is the minimum distance a building must have from the boundaries of the plot.

Occupancy, which is the maximum amount of land that a building can occupy. This is important in the case of houses. Finally, the maximum height, or number of floors. Regulations usually determine the maximum height and the number of floors above ground and basements. You will have to take this section into account if you want to create a new floor.


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