Renovating a flat is one of the most important —and most stressful— decisions you can make about a home. When it goes well, it completely transforms a space. When it goes wrong, it can turn into a months-long nightmare of blown budgets and results that bear no resemblance to what you had in mind.
The curious thing is that renovation mistakes are almost always the same ones. They don't depend on the size of the project or the budget. They depend on how it's planned, who you work with, and what decisions are made —or avoided— at each stage. Here are the most common ones, and above all, how to sidestep them.
1. Starting without a real budget
This is the most common mistake and the one with the most consequences. Many people launch into a renovation with a figure in mind based on rough estimates, comments from acquaintances, or quick quotes that don't include everything. The result is almost always the same: the final cost far exceeds what was expected.
A real budget includes the work itself, materials, professional fees, necessary permits and licences, and a contingency margin —between 10% and 15% of the total— for unforeseen issues. In structural renovations, surprises are very common once walls are opened or floors are lifted: damp, old installations that need replacing, structures that aren't where they should be.
Tip: Get at least three detailed quotes and make sure they all cover the same line items. A very low quote almost always means something isn't included.
2. Not defining the scope clearly before starting
Starting a renovation without a clear picture of exactly what you want to do is one of the most common sources of conflict between owners and contractors. Changes of mind mid-works are costly: something that would have cost nothing in the planning phase can multiply in price once work has begun.
Defining the scope means deciding in advance: which rooms are being renovated, what stays and what changes, which materials will be used, and what the expected final result looks like. The more detailed this definition is before work begins, the less friction there will be during the process.
Tip: For a full renovation, it's worth investing in an interior design project before requesting construction quotes. It will save you far more than it costs.
3. Choosing a contractor based on price alone
The lowest quote isn't always the best. Behind a price well below market rate there may be lower-quality materials, unrealistic timelines, uncontrolled subcontracting, or simply a company that doesn't have the real capacity to execute the project.
Choosing who will renovate your home is a decision that deserves time and careful judgement. Ask for references, visit previous projects if possible, verify that they are properly registered and have public liability insurance. A contractor with a solid track record and clear communication is worth far more than a cheap one who disappears halfway through the job.
Tip: Be wary of quotes that arrive within 24 hours without a prior visit to the property. A serious estimate requires seeing the space in person.
4. Underestimating timelines
Renovations almost never finish on time. This is a reality of the industry, not an exception. Delays can come from materials taking longer to arrive, trades not coordinating well, unforeseen technical issues, or simply poor initial planning.
The problem isn't that delays happen —some margin should always be built in— but that many people plan their lives around a completion date that is too optimistic. If you're between two properties or have a hard deadline, always calculate with more margin than you're given.
Tip: Add 20–30% to the estimated timeline for your personal planning. If the work finishes early, great. If not, you won't be caught off guard.
5. Not obtaining the necessary permits
Some renovations require a municipal licence and some don't. The line between the two isn't always obvious, and the temptation to skip the process —to save time or money— can prove very costly. Work carried out without the relevant permits can result in fines, an obligation to undo what has been done, or problems when it comes to selling the property.
In general, any work affecting the building's structure, the façade, the internal layout, or the installations requires some form of notification or licence. Regulations vary by municipality, so the safest approach is to consult a technical specialist or the local council before starting.
Tip: Always ask the contractor to specify which permits are needed and who is responsible for processing them. Don't assume it's included.
6. Neglecting installations in favour of finishes
It's easy to become focused on tiles, flooring, or wall colours and push into the background what can't be seen: the electrical installation, plumbing, and climate control. This is a mistake that tends to be costly, because updating an old installation once everything is finished means opening things up and closing them again.
If the property is more than twenty or twenty-five years old, the installations likely need a serious review. Taking advantage of the renovation to do everything at once is more efficient and far cheaper than doing it separately.
Tip: Before finalising the budget, have an electrician and a plumber assess the condition of the installations. The investment in that prior assessment always pays off.
7. Having nothing in writing
Verbal agreements are a source of conflict in many renovations. What was included, what wasn't, when the work was due to finish, how changes would be handled… if it isn't written down, each party remembers what suits them.
A building contract doesn't need to be a complicated document, but it should set out the scope of works, the agreed materials, the total price, the payment terms, the timeline, and the conditions in the event of any issues. It's the best protection for both parties.
Tip: Don't start any work without a signed contract. And if changes arise during the works, ask for them to be documented in writing too, along with their impact on price and timeline.
8. Making material decisions in a rush
Choosing materials once work is already underway is one of the mistakes that causes the most delays. If the tiles you want have a six-week delivery lead time and the work has been going for two, there's a problem. And rushed decisions tend to be ones you regret later.
The selection of materials —flooring, wall finishes, sanitaryware, taps, joinery— should be completely finalised before work begins. Not just to avoid delays, but to calculate the budget accurately and avoid surprises with delivery timelines.
Tip: Make a list of all the materials you need before requesting the first quote. Confirm availability and lead times before signing the building contract.
Plan today to enjoy tomorrow
A well-executed renovation begins long before the builders arrive. The difference between a smooth experience and one full of setbacks usually comes down to prior planning: setting clear objectives, establishing a realistic budget, choosing the right professionals, and anticipating potential issues. Most of the mistakes that drive up costs or cause delays can be avoided with thorough preparation and well-informed decision-making from the outset.
At aProperties, we work every day with owners who renovate their homes both to increase their market value and to adapt them to their long-term needs. Our experience has shown us that those who take the time to analyse each phase of the project before starting not only optimise their investment, but also enjoy a much smoother process and a final result that truly meets their expectations.