Interior design project: a full breakdown

What an interior design project is

An interior design project isn't a picture or a set of ideas, but a set of documents that let the site be built without improvising decisions on the spot. It includes a layout and zoning plan, a visualisation of the future space, and technical documentation: drawings, diagrams and specifications that the crew uses as an instruction manual.

The difference between an “interior idea” and a design project lies in detail taken through to construction level. A good visualisation shows what the room will look like. A design project also shows exactly where the cable runs, at what height the lighting is fixed, what material the fireplace surround is made of, and how many tiles need to be ordered. That is the difference between “nicely drawn” and “buildable without rework”.

On the service page “Interior design project” it's described as an umbrella product: a full design project brings together everything discussed further in this article. Here we're looking specifically at how the product is put together: what it consists of, how it comes about, and how it differs from adjacent services.

In essence, a design project moves the cost of a mistake from the construction stage to the design stage: a correction to the tile layout on a drawing takes an hour, the same correction after the tiles are laid takes weeks and separate money to fix. That's exactly why the section on common client mistakes at the end of this article is worth reading not as a formality, but as a list of decisions made too late.

The absence of a design project on a construction site almost always looks the same: the crew makes decisions as the work proceeds, rather than from a document. A socket ends up somewhere other than where the furniture was planned, a TV niche turns out to be the wrong width, and materials get bought as needed, without a single schedule or an agreed budget. A design project exists precisely so these decisions get made once, before work starts, not during it.

This article is written for people who are still choosing a contractor, or are only just starting to work out why a project is needed before renovating an apartment or a house at all, rather than jumping straight to a crew. Below is how the product is put together by module and stage, an honest account of the difference between a design project and adjacent services, realistic timelines, and a breakdown of the typical mistakes that stop a project from protecting the client on site.

The logic of a design project doesn't depend on the type of property: the structure is the same for an open-plan apartment in a new-build, for a detached house, and for a non-residential space. Only the depth of detail changes: a house with its own engineering and plot usually needs a larger volume of technical documentation than a city apartment, and the timeline is correspondingly longer.

What a design project consists of: 4 modules

Strip a design project down to its essence, and it has four mandatory modules.

Measurements and the technical brief. Recording the property's actual dimensions, its building services, the client's wishes and how they actually live: the foundation without which every later decision is approximate. This is also where the style and concept are defined, not as a separate, later stage, but right alongside the measurements, while nothing has been drawn yet.

Layout. Laying out functional zones and furniture with ergonomics and the way the family lives in mind. The studio often offers the client a choice of several layouts rather than one, typically two or three for different ways of using the space. More on this module is in the separate article “What's included in an interior design project”.

3D visualisation. A realistic image of the interior with materials, lighting and furniture: a way to see the result and make corrections before work begins, rather than after the fact. It's usually preceded by monochrome 3D sketches, which are used to check the geometry and composition before the final materials are even chosen, so corrections at this stage cost less than corrections on a finished colour image.

Technical documentation. A full set of drawings: floor and ceiling plans, wall elevations, electrics and low-voltage wiring, construction details and material specifications, coordinated with the building services design. This is a document for the builders, not for the client: it's used to build from, not to admire.

Running through all four modules is one more element that simplified descriptions often overlook: the procurement schedule, a table with every item in the interior, its price and a link to the supplier. It starts at the same time as the technical brief and closes about a week after the technical documentation is delivered. Formally it is a separate service, furnishing and procurement, but in practice it runs alongside the project from the first day to the last.

The modules do not exist in isolation from one another: each builds on the decisions of the one before it. A layout done without measurements risks not matching the site's real dimensions. A visualisation done without an approved layout needs reworking the moment the arrangement changes. Technical documentation done without a final visualisation cannot fix the materials and details shown in it. It is this sequence, not simply a list of four items, that sets a design project apart from a set of disconnected services.

The stages of a design project, from brief to delivery

The simplified formula “brief → layout → visualisation → documentation” really only covers the concept and technical stages. The studio's actual process is more detailed and has seven steps.

1. First meeting and contract. The first meeting, getting to know the brief and the site, and signing the contract. Work on the project doesn't begin before this point.

2. The technical brief. A questionnaire for the client, measuring the property, photographing it, analysing the building services, functional zoning, and the choice of style, concept and references, which other studios often leave to a separate, later stage while we settle it straight away. The result of this stage is a bound A3 document that the client signs as an agreed starting point. On average it takes around two weeks.

3. Layout. One or several zoning and layout options for the client to choose from, usually two or three for different ways of living. This module is covered in the article “Space-planning solution for an apartment” and in the service “Space planning”.

4. Visualisation. First monochrome 3D sketches to check geometry and composition, then the selection of materials and equipment, then the final colour visualisation with lighting design. Together with the layout, this stage takes from 20 working days for a project of around 100 m², and longer for elaborate styles such as Art Deco.

5. Technical documentation. A full set of drawings, diagrams and schedules, coordinated with the building services: ventilation, electrics and water supply. Takes around another 20 working days for a project of the same floor area.

6. Furnishing and procurement. The schedule with items, prices and suppliers is closed about a week after the technical documentation is delivered.

7. Handover for construction and design supervision. The design project is handed over to the builders, and checking that the site matches the documentation is a separate service, covered in the article “Design supervision: what it is and why a site needs it” and on the service page “Design supervision”.

Add up the usual benchmarks for each stage, around two weeks for the technical brief, from 20 working days for the concept design and another 20 or so for the technical documentation, and you arrive at roughly 2.5 months for a property of around 100 m². This is not a rigid guarantee but a planning model: the real schedule always depends on how quickly the client approves decisions at each meeting, and a delayed answer at one stage pushes back every stage that follows.

Every approval is recorded in writing, as minutes in the shared chat with the client. This isn't bureaucracy for its own sake, it's insurance: months later, both sides remember exactly what was approved and when. A more detailed breakdown of every stage is in the article “Stages of a design project: from measurement to completion”.

Who's involved in the project: the designer, the architect, the Chief Designer

A design project isn't the work of one person, but of a team with clearly divided areas of responsibility.

The interior designer runs the project from the technical brief to the delivery of the documentation: layout, style, materials, visualisation, construction details. This is the main author of the decisions, and the person the client talks to at every meeting.

The architect gets involved when the work affects load-bearing structures, involves reconfiguration or building services design, or when a house is being designed from scratch. That area of responsibility extends beyond the interior and calls for a separate qualification.

The Chief Designer oversees the project as the studio's senior specialist, checking the quality of the decisions, how the modules tie together, and whether the concept is being followed at every stage, from sketch to final drawings.

The engineer gets involved at the technical documentation and design supervision stages, wherever a design decision has to be tied in with the real engineering systems: ventilation, electrics, water supply. It is the engineer, together with the designer, who visits the site during supervision and checks the installation against the positions and heights set out in the project.

This division is not a formality. It means that the furniture layout, the engineering decisions and the final check of the drawings are each the responsibility of a different specialist, rather than one person doing everything. For the client this shows up in a concrete way: the meetings and the approval minutes make clear exactly who made a given decision and on what basis, which makes it easier to talk to the contractor if a question comes up on site.

For the client, the team also means a predictable rhythm of communication, rather than a string of random calls. The first meeting takes place at the site, every presentation of decisions is followed by minutes in the shared chat, and any changes after approval are recorded in writing. The client doesn't need to remember verbal agreements or dig them out of a week-old conversation: the whole history of decisions is documented and available at any point in the project.

Design project, space-planning project and architectural design: what's the difference

These three terms are often confused, and the difference between them decides what the client actually ends up with.

A space-planning project is only zoning and layout: how the space will be organised, where the walls, doors and furniture go. No visualisation and no technical documentation. It's a stand-alone, faster service, covered in more detail in “Space-planning solution for an apartment” and on the service page “Space planning”.

An interior design project includes the layout, but adds visualisation and a full set of technical documentation, taking the decisions all the way to a state that is ready for construction. Covered in full in this article.

An architectural design is a broader term, concerned with the building itself or its structure: load-bearing walls, façades, the building's engineering systems as a whole, not just the interior spaces. For an apartment or a house with an open-plan layout, the architectural part may be needed before the designer's work even starts, for example when load-bearing structures are being moved.

Put briefly: a space-planning project answers “how to arrange it”, a design project answers “how to arrange it, what it will look like, and how to build it”, an architectural design answers “what can be changed in the building itself”.

In practice, the choice between services depends on what's already been decided. If the client has a rough layout and only wants to check the furniture arrangement, a space-planning project is enough. If they need to see the future interior and get documents for construction, a full design project is needed. If load-bearing walls are being moved, the façade is changing, or the property is being built from scratch, the architectural part is needed first, and the designer develops the interior on that basis.

A common mistake at this point is to order the visualisation alone, expecting the crew to “finish it off from the picture”. Visualisation really is part of a design project, but on its own it fixes neither the construction details, nor the specifications, nor the positions of services, and those are exactly what the crew needs if it is not to make decisions on its own, on site, rather than at the negotiating table.

How long it takes, and what the price depends on

The development timeline depends on the property's floor area, how elaborate the chosen style is, and how quickly the client approves decisions. For a project of around 100 m², a realistic benchmark is about 2.5 months, given quick client responses at every stage: the technical brief takes around two weeks, the concept design with layout and visualisation takes from 20 working days, and the technical documentation takes around another 20 working days. On larger floor areas and in more detailed styles, the timeline grows in proportion to the volume of decisions that need to be worked out and approved. The range for each stage, across different floor areas and styles, is wider than the averaged benchmark for 100 m²: the concept usually takes 5 to 15 working days, visualisation 15 to 40, technical documentation 10 to 63. The final figure for a specific property is fixed in the contract, not taken from an averaged table.

The price of a design project is made up of several variables, not a single rate per square metre: the property's floor area, how complex the layout decisions are, the volume and detail of the visualisation, how deep the technical documentation and construction details go, and the style. The denser the decor and the more non-standard the structures, the more decisions have to be designed and drawn. The 2026 starting rate is from €50 per m². The studio works out the exact cost individually for each property, based on these parameters rather than an averaged figure.

The rate quoted is a starting benchmark, not a final estimate: a full cost calculation for a specific property deserves its own separate discussion. The other side of the question matters just as much. The cost of a design project does not include the building work itself, materials and furniture, or securing official approval for a reconfiguration. Those are separate items of cost, worked out on their own once the project is ready. Mixing up the design budget with the building budget is a common reason a client's expectations about the final renovation total end up out of line with reality.

You can discuss the parameters of your own site and get a benchmark for timeline and price structure at a designer consultation.

What happens after the project: construction and design supervision

Delivering the technical documentation is not the end of the story, it is the handover of the project to construction. At this stage, decisions made on paper meet the real site, the contractor and the materials, and this is where deviations from the approved project are most likely to arise if nobody checks the process against the documentation.

Design supervision is regular monitoring by the designer and the engineer to check that construction matches the approved project: the layout, the construction details, the positions of services, the heights and the materials. It is a checking function, not a managing one: the designer does not run the crew, but checks the result against the intent and stops deviations before they end up in the finishes.

A telling example from practice: on a routine site visit, the specialists rejected the decorative plaster on an entire floor, where bulges, bubbles and too coarse a texture did not match the project, and sent the work back to the contractor to be redone. On the same site, porcelain tiling in the lift lobbies was halted because of uneven joint widths and lippage between tiles, and the contractor was required to replace the tiling and fit the inserts specified in the project. Had there been no design supervision on that site, both defects would have gone into the finish work, and the rework after handover would have cost several times more.

In practice, design supervision isn't a one-off visit but a regular cycle: planned site visits every week, on average four to six times a month, plus unscheduled ones when needed. The minimum contract term for construction support is three months. Between visits, the team and the client stay in touch in a shared Telegram chat with the builders, and every visit is followed by a report with photo records in an electronic log, so the client always has a history of what's been checked and what's been fixed.

It's also important to be honest about the boundary: design supervision is responsible for making sure the property is built exactly as designed, matching the layout, the construction details and the materials, not for making sure construction follows building codes, for as-built documentation, or for managing contractors on time and budget. That is the domain of construction or technical supervision, a separate function that the studio does not take over.

A detailed breakdown is in the article “Design supervision: what it is and why a site needs it” and on the service page “Design supervision”.

Common mistakes when ordering a design project

Most rework on site has less to do with the quality of the project itself than with how clients handle the finished decisions once building starts. Here are the recurring situations from the studio's practice.

1. The renovation starts before the concept design and visualisation are finished. The client is in a hurry to start building while the design part is not yet fully approved, so the work proceeds “in broad strokes” and the precise decisions on materials and construction details arrive later, alongside the installation work. The result is rework and unnecessary spending in places where the decision would already have been fixed in the documentation, had building started after the project was delivered instead of running ahead of it.

2. Ordered items are changed without checking with the designer. Swapping one tile or light fitting for “something similar but cheaper” seems like a small thing, but it breaks the way the project ties together: the dimensions, construction details and layout calculated for that specific item from the schedule. The studio's systematic approach is written approval for any substitution before ordering, not after the fact, once the material has already been bought and delivered to the site.

3. Cutting corners on design supervision. The client decides that once the project is ready, the crew can manage on its own from there. Without regular checks, deviations on site build up unnoticed, as in the plaster and porcelain tile example above, and only come to light once fixing them is already expensive, rather than at the stage where a single planned visit could have prevented it.

4. Procurement is handled independently, without the studio's schedule. The client orders furniture and materials directly, going by the visualisation rather than the exact items in the specification. The result is complaints about mismatched items and missed delivery dates, because the purchasing happened without a single table checked against the project and without agreed logistics timelines.

5. Engineering is underestimated at the layout stage. Ventilation, air conditioning and humidification get planned for “later, once the layout is clear”, but if these systems aren't factored in at the zoning stage, they're hard to hide neatly and tie in with the interior later, and relocating engineering points on site costs more than it would on paper.

6. Ergonomics and installation heights are ignored. The result is “uncomfortable to live in”: furniture blocks doors from opening, the plumbing outlet doesn't line up with the fixture, and there isn't enough storage for the family's actual belongings. Technical documentation fixes heights and dimensions in advance precisely to avoid this, not just to “have something to show the builders”.

7. Client involvement drops off towards the end of the build. Once the most interesting part, choosing the style and the visualisation, is behind them, clients pay less attention to detail at handover, and that's exactly when it matters most not to lose focus: handover is the moment when a deviation can still be fixed without extra cost, not a formality before moving in.

All seven points are answered by the same principle, a systematic one: the project is finished before the renovation starts, any changes are approved in writing, design supervision runs regularly, and everything is procured against a single schedule rather than decided on the spot.

If the whole article were reduced to one thought: an interior design project isn't a formality before a renovation, it's a working tool that removes the need for the client and the contractor to negotiate by eye. The more fully every module is carried through, from measurements to technical documentation, and the more consistently the stages are followed, the fewer decisions are left to chance once construction begins.

For an apartment, a design project is put together following the same logic described above, the same four modules and the same order of stages, but adjusted for the typical constraints of city housing: load-bearing walls, ventilation shafts, approved reconfigurations in neighbouring apartments, and the management company's requirements. These details are covered separately on the service page “Design project for an apartment”.