The short answer: an interior designer plans everything inside the existing shell: spatial quality, layout, light, materials, joinery. An architect plans the shell itself and anything touching structure, envelope or building law. We have both disciplines and the construction management in our own team, and in practice the question is rarely "which one". It is usually about the point at which the second discipline joins, and who is responsible for the handover between them.
Most articles on this topic explain job profiles. That helps very little when you are standing in a Palma townhouse or a finca outside Sóller and want to know who to call first, the interior design studio on Mallorca or the architect. So this article works through concrete projects and who is responsible for each.
What an interior designer plans
In our projects, interior architecture starts with whether the existing layout suits the way someone actually wants to live, and it ends at the position of every socket. In between sit room sequences, sightlines, lighting design, the material concept, kitchen and bathroom layouts, built-in joinery detailed to the millimetre, and the full set of construction drawings the trades work from.
The difference between an interior designer and a decorator shows up at shell stage: moving partitions, rerouting service ducts or dropping a ceiling is already constructive planning within an existing building. That is our daily work in interior design.
When an interior designer is enough
For a large share of the enquiries we receive, interior design alone is enough. Typical cases:
- A full apartment or house refurbishment with no intervention in load-bearing elements.
- New kitchen and bathrooms, including rerouted services, new floors, new electrics.
- Removing or adding non-structural walls to open up a layout.
- A complete material, colour and lighting scheme, built-in storage, doors, surfaces.
- A holiday home or rental property that needs redesigning and furnishing.
The rule of thumb we use internally: as long as facade, structure, roof and building volume stay untouched, it is an interior project. The moment one of them is altered, it becomes an architecture project, even when it feels to the owner like "just a renovation".
When you need an architect
You need an architect as soon as the building itself changes. As a rule that applies to:
- Opening load-bearing walls, forming openings with a new beam, cutting a slab for an internal stair.
- Extensions, added storeys, loft conversions, new dormers or enlarged window openings.
- Change of use: commercial to residential, attic to habitable space.
- New build, demolition and replacement.
- Anything requiring a building permit or a formal notification to the authority.
- Work on listed fabric or on a facade in a protected area.
Here the architect delivers a permit-ready set of drawings, the coordination with structural and services engineers, and the dialogue with the authority. What exactly has to be submitted depends on the municipality and the scope, which is why we settle it on the specific property rather than over the phone. More on our architecture page.
When you need both, and where mistakes happen
Many projects fall in between. An opening between kitchen and living room in an old building is a structural question and a question of proportion at the same time. A finca receiving a new terrace opening is a facade decision and a decision about how afternoon light lands in the living space.
When those two sets of plans come from two separate offices, often nobody takes responsibility for where they meet. In our projects we see the same patterns repeatedly when owners have appointed designer, architect and builder separately:
- The opening is structurally correct but a few centimetres too low for the kitchen run that was designed for it.
- The builder's electrical layout ignores the lighting design because it was finished first.
- The screed build-up rules out the specified floor finish, because nobody asked the interior team about levels.
- When something slips, each party points at the other, and the owner ends up mediating.
These mistakes rarely come from poor work. What is missing is someone responsible for the handover between the parties. That is why we keep design and construction management together: whoever detailed it is also on site when it is built.
Mallorca: fincas and townhouses
Most owners who come to us on Mallorca are buying or have just bought, and the split between the two disciplines is sharper here than in a city apartment.
A rural finca is almost always an architecture project as soon as the volume is touched: rubble stone walls, irregular geometry, later additions with incomplete documentation, and rules that differ between municipalities and depending on the protection status of the plot. Permits generally involve the town hall and, depending on the scope, further bodies, so it is best to have the planning position checked before you buy. We wrote about that sequence in renovating on Mallorca: a guide for international owners.
A Palma townhouse is the opposite case: narrow, deep, dark in the middle, with a patio or light shaft as the only source of daylight for the central rooms. Here the interior planning makes the biggest difference: where the stair goes, which openings connect the levels, and which materials cope with ground-floor humidity. Move the stair or open a floor slab, and the architect is back in the picture. Our renovation service page sets out how we run those projects, and the Mallorca page covers how we work on the island.
Berlin: Altbau and what the building allows
Berlin Altbau apartments are generously proportioned but rarely laid out for how people live now: small kitchens, bathrooms retrofitted into service rooms, corridors consuming a disproportionate share of the floor area. What makes them valuable is usually the ceiling height, the cornices and the windows. The floor plan is rarely their strong point.
What turns into an architecture question quickly in Berlin: load-bearing walls in period buildings are rarely where you assume; the joist direction dictates where a bathroom can sensibly sit; and facade, windows or courtyard elevation bring heritage protection, conservation-area rules and owners'-association decisions into play. Inside the apartment you usually have room to move; at the envelope, almost none. If you are comparing studios there, 7 questions to ask before hiring an interior designer in Berlin Mitte covers what to check, and our Berlin page sets out how we work locally.
Decision table: who do you need?
| Project | Who you need |
|---|---|
| Redesign an apartment, layout stays | Interior designer |
| Full new kitchen or bathroom | Interior designer (with services planning) |
| Remove a non-structural wall | Interior designer |
| Open a load-bearing wall | Architect + structural engineer, interior design for the result |
| Loft conversion, extension, added storey | Architect, then interior designer |
| Facade, windows, listed building | Architect |
| Change of use | Architect |
| Finca renovation altering the volume | Architect + interior designer + construction management |
| Palma townhouse, interior only | Interior designer |
| New build | Architect, interior designer from concept stage |
FAQ
Do I need an architect for a renovation?
Only if the renovation changes the building itself (structure, facade, roof or volume), or if it needs a building permit or formal notification. If everything stays inside the existing shell, an interior designer can normally take the project from concept to completion. At CARLO Design we establish that boundary on the property during the first visit, because a mistake at this point costs the most to put right later.
What is the difference between an interior designer and an architect?
An architect is responsible for the building: structure, envelope, volume and permit-relevant planning. An interior designer is responsible for the space inside it: layout quality, light, materials, joinery and the detailed construction drawings. We run both disciplines in one team, because most mistakes in a renovation happen where the two meet.
Can an interior designer manage a renovation?
Yes, provided the practice offers construction management as a service and stays involved after handing the drawings to the builder. In our projects the same team that detailed the interior runs the site, coordinates the trades and checks the work against the drawings. With one team responsible, a specified finish is less likely to be swapped for a cheaper substitute without anyone noticing.
Should the architect and interior designer be the same firm?
Not necessarily, but somebody has to own the interface between them, and in split appointments that role usually falls to the owner by default. The mistakes we keep seeing on renovations are rarely design mistakes. They happen at the handover between parties appointed separately. Keeping architecture, interior design and site management under one roof removes that gap, and gives you one person to call.
Your next step
If you are not sure which category your project falls into, we can settle that in a first conversation. We look at the property, tell you whether you need an architect, and give you a cost estimate checked against prices from our contractors, before you commit to anything. Get in touch, in Berlin or on Mallorca.
What your own project will roughly cost, you can work out in two minutes. Work out your budget →