The most common apartment renovation mistakes, and how to avoid them

In a renovation, mistakes do not all carry the same weight. Some are discovered the following week and fixed with a conversation. Others only become visible once the furniture is in place, and the only way to resolve them is to reopen a wall that has just been painted.

That is why this guide is not a list of ten points in order of importance. It is organised by the moment each mistake happens, because that moment determines the cost of fixing it: a badly defined scope before the start costs a meeting, the same badly defined scope in week six of the work costs demolition, wasted material and delay across every trade that was due to follow.

The criterion behind this guide The three phases are what gets decided before starting, what goes wrong while the work is under way, and what only becomes apparent after moving in. The third is the least discussed and generates the most regret, because by the time it appears there is no open site left to resolve it.

Phase 1: before starting

This is the phase with the best ratio of effort to result: everything resolved here is resolved on paper.

Starting without an overall view of the flat

This is the mistake most often cited by people in the trade and also the easiest to underestimate, because it does not look like a mistake: it looks like pragmatism. You start with the kitchen, the thing that bothers you most, and leave the rest to decide “when we get there”.

The problem is that the work does not wait. With the scope still open, decisions end up being taken with the teams already on site and under calendar pressure, and in those conditions you choose what is available rather than what makes sense. Each late decision drags the next along: moving the worktop position forces water points to move, which forces sockets to move, which forces already-laid finishes to be reinstated.

The alternative does not require a full architectural design. It requires a plan of the whole flat, including the rooms nothing will happen in, with four things decided: where each function goes (sleeping, cooking, working, storage), where the main furniture goes, which walls stay, and where the water points are. With that settled, what remains are material choices, which are reversible, rather than layout decisions.

A vague quote, with no breakdown by section

A quote that closes the job at a single figure is impossible to verify: you do not know what is included, you cannot compare it with another proposal, and there is no way to discuss a change without renegotiating everything. It is also the format that most feeds additional work midway, because nothing was described precisely enough to claim it was covered.

What a quote should have is the work divided into sections (demolition, plumbing, electrics, finishes, painting, joinery, final clean and debris removal), each with quantities, identified materials and a figure. It is that division which later allows additional work to be distinguished from work already contracted.

Not allowing slack for the unexpected

In a flat of any age, part of what sits behind the walls is only known once they are opened: degraded pipework, damp in a party wall, floors well out of level. None of these is rare and none appears on a pre-work visit. Slack of between 10 and 20% of the value of the work avoids having to choose between halting the job and cutting an item already decided. To place your own case, and see which items fall outside the per-square-metre figure, the per-m² prices and the sums for a two and three-bedroom flat are in a guide of their own.

Choosing the contractor on the lowest price

A 10% difference between proposals can be explained by efficiency or margin. A 40% difference almost never can: either the materials are not the same, or the labour is not equally qualified, or items are missing that will reappear as extra cost. Before comparing totals, compare scopes section by section and confirm the company’s registration, insurance and history. We have gathered what to check and which documents to ask for before signing in a separate guide.

Phase 2: during the work

From here on, every correction carries a physical cost: work has been executed, material applied, and teams scheduled one after another.

Changing the scope midway

Changing your mind during the work is natural. A demolished space looks bigger than it did on the plan, and the urge to take the opportunity to do one more thing is common. What is rarely anticipated is the chain effect: moving a partition wall half a metre can mean redoing the electrical layout in that area, delaying the plasterer, holding up the painter who was next, and releasing the team to another job, which means waiting for their next available window. The direct cost of the change is a fraction of the total: the rest is in lost time and redone work.

This does not mean nothing can change. It means any change should be treated as a formal decision, with the cost and the impact on the timeline in writing before anything is carried out. A change agreed verbally on site is the most frequent origin of the arguments that surface at the end.

Neglecting what stays hidden behind the walls

A renovation is not only aesthetic. Pipework, electrical installation, insulation and ventilation are the item least visible in the final result and the one that most determines whether the flat will be in good shape ten years from now.

The temptation to skip this part is understandable: it does not photograph and it consumes a significant slice of the budget. But the arithmetic does not favour deferring it, because the larger cost of redoing pipework or electrical circuits is not the material, it is opening up floors and walls and then reinstating the finishes. Anyone who lays a new floor and paints everything, only to have to open the same wall two years later, pays for that finish twice.

There are concrete signs that take this decision out of the realm of preference: old iron or lead pipework, a consumer unit with no separate circuits, recurring damp patches, or bathrooms with no effective extraction. Ventilation tends to be the forgotten one of the four and is the one that shows itself fastest, in the form of mould.

This is also where the choice of renovation level stops being a matter of taste: choosing a light scope for a flat that needs new infrastructure is, in practice, deferring that infrastructure. The difference between the three levels is explained in what changes between a light, mid and deep renovation, which helps you see whether the level chosen really covers the state of the property.

Economising on materials that wear out quickly

Not every material justifies the same investment, and the useful criterion is not price per square metre: it is what it costs to replace that item five years from now. Lower-grade paint is repainted over a weekend and a cheap tap is swapped in an hour. But flooring that warps with kitchen humidity, badly executed waterproofing, or hinges that give way after two years mean dismantling, removing and reinstalling, with all the finishing work that drags along.

Hence the practical rule: economise on what is on show and can be swapped without building work, invest in what sits underneath, inside or behind. That includes waterproofing, pipework, cabinet hardware and flooring in wet areas.

Working without stages or a fixed timeline

The renovation that never ends is a real and recurring problem. There is, right now, a public discussion on the Fórum da Casa dedicated to exactly this, titled “A eterna remodelação”, which gives a sense of how many people find themselves in this position.

The mechanism behind it is almost always financial: when the amount already paid runs ahead of the work executed, there stops being any practical reason for the team to prioritise that job over the next one. The work is not abandoned, it advances when there is spare capacity.

What prevents this is contract structure, not insistence. Three elements resolve most cases: a fixed price in writing before the start, a work plan with stages and associated dates, and payments released only when each stage is complete and verified on site. That way, at any moment the money handed over corresponds to work you can see. A single project manager coordinating every trade resolves the other half of the problem, the sequence between them: the electrician has to come before the plasterer, the plumber before the waterproofing, and a delay on one front propagates to every one that follows.

Phase 3: what only shows after moving in

These are the mistakes nobody spots at the final inspection. The flat looks immaculate and nothing seems missing. The problem appears in the first week of normal life, and by then there is no open site left to resolve it.

Sockets and power points planned last

This is the most frequent mistake of this phase, and it comes from an inverted order. Power points are usually defined with the work already under way, after the flooring has been chosen and without the furniture being settled. The installation follows the default pattern, one socket per wall, and only afterwards does it become clear where life actually happens.

The correct order is the reverse: first decide where the sofa, the bed, the television, the desk and the appliances go, and only then mark the power points on the plan. It is an afternoon’s conversation that has to happen before the electrician runs any cable.

When this fails the result is not dramatic, it is permanent: extension leads under furniture, chargers competing for the same socket, and cables crossing skirting boards. It is worth planning sockets on both sides of the bed, beside each end of the sofa, at the point where you work and along the kitchen worktop. Adding them during the work has a marginal cost; afterwards it means chasing, replastering and repainting.

Lighting treated as a detail

Lighting usually enters the conversation at the decoration stage, when light fittings are chosen. By then, what counts is already inside the walls: how many light points exist in each room, where they are and which switches control them.

A room with a single central point serves to light everything evenly and little else. It does not serve for reading on the sofa, working at a desk or cooking with the worktop properly lit. That requires different layers (general light, task light, indirect light) on separate circuits, so you can switch on only what you need. Fittings can always be changed, but adding a light point where no cable was run means opening a ceiling or a wall. The lighting plan is decided at the same time as the sockets, and for the same reason: it depends on where the furniture will be.

Not enough storage

When planning, attention concentrates almost entirely on the social areas. The living room and kitchen are the rooms imagined and discussed in detail; storage is left to the end, with whatever space remains.

But storage is not a room, it is a quantity: unless it is counted in linear metres of cupboard and in usable volume, the sums do not add up. And they add up even worse when wardrobes are removed to gain apparent floor area, or when a pantry is knocked through to open the kitchen onto the living room. This only becomes obvious on moving day, when the boxes come off the van and there is nowhere to put them, and from that point the solution is always worse: standalone furniture bought in a hurry, taking up floor area and never quite fitting.

The exercise that avoids this happens before the work. List what actually exists (clothes for each season, bed linen, crockery, cleaning products, tools, bicycle, vacuum cleaner) and check, room by room, where each category will live. Habitually wasted zones, such as the space above doors, the hallway, or the height between wardrobe and ceiling, resolve much of the problem when they enter the plan from the start.

Focusing only on looks and forgetting how it is used

The three previous mistakes are particular cases of the same pattern: deciding on appearance and checking use too late. It shows up in other common choices too: a kitchen worktop that is handsome but short, with no landing space between hob and sink; a bathroom with high-end tiling and no surface to put down what you use every day; a pale matt floor in a home with animals or children.

The check that catches nearly all of these is done on the plan, before ordering material: walk mentally through a normal day, room by room. Arriving home with shopping bags, cooking a full meal, running a load of laundry from start to finish, getting ready in the morning with someone else using the bathroom. Wherever the route snags, there is a detail to resolve while it is still cheap.

Summary: mistake, consequence and when it can still be fixed

Mistake	Consequence	Fixable without building work until
No overall view of the flat	Decisions under pressure, with a chain effect	Before the start
Quote with no sections	Proposals impossible to compare	Before signing
No slack for the unexpected	Work halted or items cut	Before the start
Scope changes midway	Redone work and propagated delay	Only in writing, with cost and timeline
Hidden infrastructure deferred	New building work a few years later	While the walls are still open
Fast-wearing materials	Early replacement with building work attached	Until the order is placed
No stages or deadlines	Work that drags on with no end date	In the contract
Sockets decided last	Extension leads and visible cables, permanently	Before the electrical installation is run
Lighting left to the decoration stage	A single layer of light, no separate circuits	Before ceilings and walls are closed
Storage left over from the rest	Standalone furniture bought in a hurry	While the plan can still change