Internal staircases in Spanish duplexes: types and sizes
The staircase is the most expensive piece of furniture in a duplex and the only one you cannot return. It gets decided once — with the regulations and the floor structure in front of you.
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Short answer
Which internal staircase fits, and how much space does it take?
For a duplex or attic flat, a straight staircase is the most comfortable and takes the most floor — about 3.5–4.5 m² with its landings; a quarter-turn (L-shaped) shrinks the footprint and hugs a corner; a spiral drops below 2 m² but is awkward daily and hostile to furniture. Catalan habitability rules ask for treads of at least 22 cm, risers of at most 20 cm and a clear width from 80 cm inside a dwelling. Fitting a staircase into an existing void is days of work; cutting a new opening in the floor slab is major works with a structural project — the territory of a full renovation, at €780–1,600/m² and 10–14 weeks.
The staircase competes for metres with everything around it — the right question is not which looks best but which fits daily use: carrying shopping up, coming down half asleep, moving a mattress once a year.
| Type | Footprint | Daily comfort |
|---|---|---|
| Straight | Largest, 3.5–4.5 m² | Best: constant rhythm, continuous handrail |
| L-shaped (quarter turn) | Medium, hugs two walls | Good; the landing splits the effort |
| Spiral | Smallest, from 1.5–2 m² | Tight: hard with loads, children or age |
| Floating / retractable | Minimal | Only for lofts used occasionally |
Measurements
The numbers the law sets and the numbers your body sets
There are two bars: the legal one — habitability — and real comfort, which is stricter. Meeting only the first produces staircases that are legal and unloved.
Worth respecting
- Treads of 25–30 cm and risers of 17–18: the natural step of an adult
- Clear width of 80–90 cm; at 70 you can climb, but not pass another person or carry a wardrobe
- Head clearance of 2.20 m along the whole flight: heads do not negotiate
- Handrail at 90 cm with gaps that cannot swallow a child’s head
- Its own lighting, with switches at the top and the bottom
The original sin
Drawing the staircase last, once the layout is closed. The staircase goes in first — with its landings top and bottom — and the layout is built around it. Done backwards, you get 21 cm risers and 1.95 m head heights that collect a bruise a week.
The legal layer
Joining two flats: what cutting a slab really means
In an existing duplex the staircase already has its void. Cutting a new opening — typically to join two flats bought one above the other — is a different league, because the floor structure does not belong to you: it belongs to the building.
What it involves
- The slab is a common element, so the community of owners must authorise the cut — usually at a general meeting, and your vote can be delegated by proxy if you are abroad
- A structural engineer calculates the opening, the cut joists are reinforced around a new steel frame, and the job runs under a major-works licence with professional site direction — not a same-day notification
- The slab type decides the method: concrete-joist floors take a framed cut well; Catalan timbrel vaults spread loads differently and the opening is planned differently from the first sketch; in 1950s–70s buildings the cut is the moment to test for aluminous cement
- Two flats joined physically can later be merged legally at the land registry; mortgages and each flat’s cedula — the habitability certificate — are checked before anything is cut
Under the stairs
The space under the flight is one of the few gifts a staircase makes: a fitted wardrobe, a laundry corner, a pantry. Design it with the staircase, not afterwards — the fronts depend on the exact pitch of the flight. A spiral leaves nothing usable.
Frequently asked
Common questions
A comfortable straight flight, about 3.5–4.5 m² including landings; an L-shape slightly less by using a corner; a spiral from 1.5–2 m². Add the clear void above the flight: 2.20 m of head clearance along the whole projection.
For comfort: treads of 25–30 cm, risers of 17–18 and a clear width of 80–90 cm, with tread plus two risers landing between 62 and 64 cm. The habitability minimums are laxer; building to the bare minimum produces stairs nobody enjoys.
Yes — with a structural project, reinforcement of the cut slab, a major-works licence and the building’s authorisation, since the structure is a common element. Feasibility depends on the slab type, and in older buildings a test for aluminous cement is done while the slab is open.
Legally yes, if it meets the habitability minimums; in practice it only makes sense when the upper floor is secondary. For bedrooms in daily use, the awkwardness with loads, children or age is paid every single day.
Yes. The staircase itself is fabricated off-site from a survey, the community vote can be handled by proxy, and the structural stage verifies well in photographs: ask for images of the steel reinforcement before the ceiling closes. Payments follow milestones, as with any works contract.
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