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How do I know if I can enlarge my house

How do I know if I can enlarge my house. It’s common to find ourselves in a situation in which our house is too small, and it’s not the same to look for a house as a single or with your partner, than to do it once we have formed a family. Given the exorbitant prices of sale and rent of apartments that we find today, it’s logical that most choose to renovate or expand their current home to gain that extra room or bathroom. But while renovating a house can be done in almost any situation as it’s a minor work, extending a house is a very different story.


To extend a house you need a project, an architect and a building permit, no matter if we are talking about a villa or an apartment in a residential building. In most cases, in order to make an extension, we need to intervene in the structure. 


In cases where light enclosures (sometimes removable) are created to close terraces, roofs or patios, although we do not alter the structure, we do modify the appearance of the facade and change the amount of floor area, so a project is still necessary. If, in addition, the house to be extended is within a community of owners, the permission of the same is required to carry out the works.


What does it depend on whether an extension is legal or not?


Erisa-How do I know if I can enlarge my house-What does it depend on whether an extension is legal or notThe legality or illegality of an extension depends essentially on the town planning regulations that affect our house.


This regulation can be consulted freely on the web of our corresponding city council and, if we do not find it, we can always go directly to speak with a technician of the city council so that it facilitates the data that we want to know. 


The information that we must obtain is the following:


Buildability, How do I know if I can enlarge my house


It’s the relationship between the square meters of land of a plot and the square meters of roof that can be built within that plot. Usually the promoters completely exhaust the buildability of the plots since it usually means a higher profitability, but the regulations are changing over the years and it’s not strange to find that our plot has plenty of buildability. 


This data can be very complicated to understand because each regulation specifies exceptions of rooms that do not count for the buildability, either totally or partially, such as, for example, storage rooms, parking, stairs, balconies, terraces and more.




Erisa-How do I know if I can enlarge my house-Setbacks

This is the minimum distance that a building must have with respect to the boundaries (edges) of the plot.


Usually the setback for the top floor of the building is greater than for the rest of the floors, so penthouses are usually more recessed with respect to the facade line.


Occupancy, How do I know if I can enlarge my house


This is the maximum percentage of land that a building can occupy within its plot. Normally this data is only relevant in the extensions of single-family houses when you want to create a new building volume attached to the existing one.


Number of floors and maximum height


This is the easiest data to understand. The majority of urban planning regulations set the maximum height (or cornice height) that a building or dwelling can have, as well as the maximum number of floors, both above ground and below ground (basements). If our intention is to expand by creating a new floor we must be very attentive to this section.


What is the first thing I should do if I want to enlarge my house?


Erisa-How do I know if I can enlarge my house-OccupationTo make sure that you do not make any mistake that could cause you problems in the future, the most advisable thing to do is to talk to the town hall and contact an architect. If you live in a small town it’s very likely that in your town hall you can speak directly with a technician who will provide you with all the necessary information. 


If, on the other hand, you live in a big city you will probably have to make more than one trip to the town hall to get the information you are looking for, and talking to the technicians can be very complicated.


Once we have spoken to the relevant town hall it’s time to contact an architect. The architects will take care of checking the data of the urban planning regulations and verify the feasibility of the extension. In addition to carrying out the corresponding project and obtaining the necessary licenses.


Why are there so many extensions in cities?


Erisa-Why are there so many extensions in citiesUnfortunately, many people, when they want to extend their house, do not turn to an architect, nor do they approach their town hall to know with certainty and security if they can make the extension. 


Most go directly to a construction company to get a budget to do it. If the builder has a certain reputation or size, he will probably advise the owner of the necessary licenses and refuse to do the work without them.


But if we contact the typical neighborhood builder, he will be happy to accept the job even knowing the consequences (if he knows what they are).


What happens if I enlarge my house without the necessary permit?


Erisa-BuildabilityTown halls are becoming more and more involved in the search for illegal extensions, what at first seemed like an easy problem to ignore is now getting out of hand and can be dangerous.


For this reason, more and more aerial flights, either with satellites, airplanes, drones or helicopters (the latter two allow 45º views so that terraces can be seen), are made every day to monitor uncontrolled and illegal growth in cities.


If the municipality discovers your extension, either by a neighbor’s complaint or by aerial photos, and it turns out to be illegal, the following can happen:




This is the best case scenario, the extension you have made was not licensed but could have been. If this is your case all you need is to legalize the extension, for which you need an architect to make the project of the work already done. 


You will have to pay the project, the license fees and an increase on these depending on the time that has passed since the works were done. The costs of the fees depend on each municipality and some may not even consider the increase or fine.


Fines, How do I know if I can enlarge my house


Erisa-Number of floors and maximum heightThis is the intermediate case, you have made an extension to your house, the town hall knows about it and there is no way to legalize it.


When this happens the town hall technicians will contact you so that a demolition of the extension can be carried out and the original state of the house can be restored. 


If the extension does not cause problems to the building, the plot or the neighbors the most usual thing is that the town hall will start to send you fines in compensation for the illegal work and leave aside the demolition.




This is the same case as above, the fines, only here the extension is causing some kind of problem and the council will demand the complete demolition of the extension. It does not need to be a serious problem such as an overweight building damaging the structure of the building, something as simple as the extension causing a leak to the neighbor below may be enough. It’s rare that it comes to these extremes and in most cases it’s solved with fines, but it’s important to know that this can happen.

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