CTE DB-SUA Staircase Regulations Spain — The Complete Architect's Guide

Continox central spine staircase engineered to CTE DB-SUA Sección 1 — uso restringido configuration, frameless glass balustrade 90cm height, oak treads 100mm thick

Spanish staircase design lives or dies by the CTE DB-SUA. Every modern staircase, balustrade and handrail in Spain — whether in a Marbella villa, a Madrid apartment building, a Barcelona office tower or a Mallorcan finca conversion — must satisfy the geometric, structural and accessibility requirements of Documento Básico SUA Sección 1 (Seguridad de Utilización y Accesibilidad — Sección 1: Seguridad frente al riesgo de caídas).

This guide covers everything Spanish architects and building professionals need to know: the two use classifications and how they affect dimensional limits; the regla de oro ergonomic formula and where it applies; balustrade height, sphere rule and climbability requirements; handrail (pasamanos) rules including when both sides are required; curved-tread geometry; and the major July 2024 update that introduced new accessibility comments currently in force.

For background on Continox's supply-only B2B model for Spain, see our Modern Staircase Spain hub. For region-specific pricing and project examples, see our Marbella & Costa del Sol guide. For the wider UK product range, see /modern-staircase/, /glass-balustrade/ and /external-staircase/.

What CTE DB-SUA Is — and Why It Governs Spanish Staircase Design

The Código Técnico de la Edificación (CTE) is Spain's national building code, established by Real Decreto 314/2006 of 17 March 2006 and modified multiple times since. Within the CTE, Documento Básico SUA — Seguridad de Utilización y Accesibilidad (Basic Document on Safety in Use and Accessibility) sets out the safety and accessibility requirements that buildings must satisfy to be granted Building Control approval.

Sección 1 of DB-SUA is dedicated to Seguridad frente al riesgo de caídas — the protection of building users against fall risks. This section governs not just staircases but also ramps, fixed ladders, mezzanine guarding and balcony balustrades. For staircase design specifically, the relevant articles are:

• Article 4.1 — staircases of uso restringido (restricted use)
• Article 4.2 — staircases of uso general (general use), including geometric, dimensional and operational requirements
• Article 3.2 — balustrades (barreras de protección) including height, climbability and sphere-rule provisions
• Article 4.2.4 — handrails (pasamanos)

Legal Framework — Why Compliance Is Non-Negotiable

CTE compliance is not optional, advisory or aspirational. Real Decreto 314/2006 establishes CTE as obligatory technical regulation for all buildings in Spain — new build, renovation, change of use, extension. Without demonstrated CTE compliance, a Spanish-registered arquitecto director de obra cannot sign off the Certificado Final de Obra, which means the building cannot be legally occupied, registered, or sold.

For staircases, this translates into a hard requirement: every step of every staircase in every Spanish building must satisfy DB-SUA Sección 1 dimensional limits. There is no "tolerance band". A huella of 21.5cm in a uso restringido application is non-compliant — even though it falls only 0.5cm short. The architect of record bears full legal responsibility for this verification.

How DB-SUA Relates to Other CTE Sections

DB-SUA does not exist in isolation. For a complete staircase compliance schedule, an architect typically references:

• DB-SUA (Safety in Use & Accessibility) — geometric and balustrade requirements, this guide's focus
• DB-SI (Safety in Case of Fire) — Sección 3 governs evacuation widths; staircases serving as fire escape routes have stricter width requirements based on occupant load
• DB-SE (Structural Safety) — load combinations, including Eurocode-aligned variable loads on stair treads (typically 3.0 kN/m² uniformly distributed for residential, 4.0 kN/m² for commercial)
• DB-HR (Acoustic Protection) — relevant where staircases penetrate floor slabs in residential buildings

Use Classifications — Uso Restringido vs Uso General

The single most important decision in CTE staircase design is determining whether the staircase falls under uso restringido or uso general. The dimensional limits, ergonomic requirements and balustrade rules differ substantially between the two.

Uso Restringido — Restricted Use

An escalera de uso restringido is a staircase whose use is limited to a small, defined group of users in a private or controlled context. The most common application is the interior of a single dwelling (vivienda) — the staircase connecting ground floor to first floor inside a Marbella villa, a Madrid duplex or a Mallorcan finca falls into this category.

Other typical uso restringido applications:

• Service staircases (escaleras de servicio) — used only by maintenance or staff, not the public
• Internal staircases in commercial offices connecting two floors used by the same tenant (some interpretations apply)
• Mezzanines within a single dwelling

The dimensional requirements per DB-SUA Article 4.1 are:

Uso General — General Use

An escalera de uso general is a staircase serving a building zone open to the public, to multiple tenants, or to undefined groups of users. This includes:

• Communal staircases in apartment blocks (zonas comunes de uso Residencial Vivienda)
• All staircases in commercial, sanitary or public buildings
• All staircases in schools, kindergartens and care facilities
• Staircases in hotels, restaurants, retail and public concurrence venues
• External public staircases serving more than one dwelling

The dimensional requirements per DB-SUA Article 4.2 are substantially stricter:

Why the Distinction Matters in Practice

For a typical Marbella villa staircase, uso restringido applies — the staircase is internal to a single dwelling, used by the family and guests of that household only. This is why Continox can supply floating central spine staircases with open treads, slim 100mm tread profiles and frameless glass balustrades in luxury villa applications: the open-riser configuration that would be illegal in a uso general staircase is fully compliant under uso restringido.

For a Madrid apartment building common stair, uso general applies — the staircase is used by residents of multiple dwellings plus visitors, postal workers, delivery personnel etc. This means closed risers, ≥28 cm tread depth, ergonomic ratio compliance, and minimum 100 cm width. Most modern villa-style floating staircases cannot be specified in uso general applications.

U-shape central spine staircase configured for uso restringido — huella 26 cm, contrahuella 17.5 cm, anchura 110 cm, frameless glass balustrade 90 cm

Geometric Requirements — Huella, Contrahuella & Ergonomic Formula

The geometric heart of CTE DB-SUA is the relationship between huella (tread depth — the horizontal walking surface) and contrahuella (riser height — the vertical face between treads). The dimensional limits and the ergonomic formula together define what a "comfortable, safe staircase" means in Spanish regulation.

Measurement Conventions per Article 4.2.1.1

How huella and contrahuella are measured is itself regulated. Common errors arise from mismeasurement:

• Huella is measured in the direction of travel — the horizontal projection of the foot's path on each tread
• Huella does NOT include the projection of the upper tread — overhang from the step above does not count toward the dimension below
• Contrahuella is measured vertically — from finish surface of one tread to finish surface of the next
• Width is measured between walls or balustrades — handrails do not reduce the measured width provided they protrude no more than 12 cm into the space
• In curved sections, huella is measured at the staircase axis if width <1 m, or at 50 cm from the narrow edge if width ≥1 m

The Ergonomic Formula — Regla de Oro

For uso general staircases, the relationship between contrahuella (C) and huella (H) must satisfy:

The formula is grounded in human gait research: 2C + H approximates one stride length. A stride that's too short (2C+H < 54) produces excessively shallow steps and increased perceived exertion. A stride too long (2C+H > 70) creates risers too tall for a single comfortable step, increasing fall risk especially when descending.

Worked Examples — Spanish Villa Staircases

Two real Continox project specifications illustrating CTE-compliant geometry — see our Marbella supply guide for additional Costa del Sol project examples and pricing:

Consistency Within a Staircase

CTE-compliant central spine staircase with uniform geometry — huella and contrahuella consistent across all flights per Article 4.2.2

DB-SUA Article 4.2.2 requires uniformity within and between flights:

• All steps in straight flights must have identical huella
• All steps in a single staircase must have identical contrahuella
• Between two consecutive flights serving different floors, contrahuella variation must not exceed 1 cm (effectively requiring identical risers throughout multi-storey staircases)
• In mixed straight-curved flights, the huella measured on the axis in curved sections must not be less than the huella in the straight sections

Width, Pitch & Maximum Rise per Flight

Minimum Widths by Use

The minimum useful width (anchura útil) of a staircase tramo (flight) is determined by occupant evacuation requirements per DB-SI Sección 3, plus the minimums in DB-SUA Article 4.2.2.4 Tabla 4.1:

For evacuation calculations, the actual width may need to be larger than the table minimum — the architect of record performs the DB-SI evacuation flow calculation based on occupant load and confirms which figure governs.

Maximum Rise per Flight

DB-SUA Article 4.2.3 limits the height a single tramo (flight, between landings) may climb:

• 3.20 m maximum in general cases — i.e. when a lift is provided as alternative to the staircase
• 2.25 m maximum in public zones, in schools (primary/secondary), and whenever no lift alternative exists
• 2.10 m maximum in kindergartens, primary schools and buildings primarily used by elderly people

For taller stair runs, intermediate mesetas (landings) are required. Each landing must be at least the width of the staircase, with depth ≥1 m for straight runs (≥1.20 m if a 180° turn occurs, ≥1.60 m in hospitalisation zones with 180° turns).

Minimum Steps per Flight

Each flight must contain at least 3 peldaños (steps). Single-step or two-step flights are not permitted because they create an unexpected level change that significantly increases trip risk. Where a level change is small, ramps or single steps with high-contrast nosing must be used instead, designed under separate ramp provisions.

Tread Edge Treatment — No Bocel

DB-SUA Article 4.2.1.4 prohibits bocel — the rounded or projecting edge profile sometimes added decoratively to step nosings. Treads must have a square or chamfered edge with no projection beyond the riser plane.

For uso general and evacuation staircases, risers must be continuous and vertical (or inclined ≤15° from vertical). Open-tread (no riser) configurations are not permitted in evacuation routes.

L-shape staircase with quarter landing — meseta dimensions per Article 4.2.3 (≥1.20 m for 180° turns), max rise per flight 3.20 m

Balustrade Requirements — Height, Sphere Rule & Climbability

Balustrades (barreras de protección) are governed by DB-SUA Article 3.2. The provisions cover height, structural resistance, sphere-rule penetration and — critically — climbability prevention in residential and child-frequented buildings. Similar provisions apply to balcony railings and external staircases serving primary access roles.

Minimum Height

Balustrade height is measured vertically from the walking surface (or, on a staircase, from the line of inclination connecting the tread nosings) to the top of the protective barrier:

For most domestic and commercial staircase applications, the 90 cm minimum balustrade height applies. This is the dimension Continox designs to as standard for villa applications. For luxury villas with double-height stairwells where the ground-to-balcony fall exceeds 6 m, balustrades upgrade to 110 cm minimum.

Sphere Rule — Maximum Opening

DB-SUA Article 3.2.3.1.b is the famous "Ø10 cm sphere rule". No opening within a balustrade may admit a sphere of diameter greater than 10 cm. This regulation exists to prevent small children from passing their head through balustrade openings — the head, being the body's largest fixed-diameter element, is the limiting factor.

The rule applies throughout the balustrade: between vertical balusters, between horizontal rails, between the bottom rail and the floor, between mid-rails, and between the top rail and any wall or ceiling. The 10 cm diameter is checked using a physical or digital sphere model at every accessible opening.

Climbability Prevention

In residential buildings, schools and zones frequented by children, balustrades have additional design requirements per DB-SUA Article 3.2.3.1.a — they must not be "easily climbable":

• In the height band 30–50 cm above floor level (or stair line of inclination), there must be no points of support or projections greater than 5 cm
• In the height band 50–80 cm, there must be no projections with a substantially horizontal surface greater than 5 cm in depth (which a child could stand on)

This rule is why horizontal balustrade bars are typically prohibited in residential applications — they create a "ladder" effect children can climb. Vertical balusters or full-height frameless glass panels are the compliant alternatives.

Glass Balustrade Specifications

For frameless glass balustrades (Continox's signature villa specification), the glass itself must be:

• Tempered laminated glass — typically 2× 8mm tempered with 1.52mm SGP or PVB interlayer (16+ mm total) for free-standing applications
• Compliant with EN 14449 (laminated glass) and EN 12150 (tempered glass)
• Engineered to withstand horizontal line load per DB-SE-AE Article 3.2.1 (for residential balustrades, 0.8 kN/m horizontally applied at handrail height)
• Detailed with structural calculations signed by a Chartered Structural Engineer — Continox supplies these as part of the technical pack for every project

For more on frameless glass balustrade engineering, see our Glass Balustrade page covering frameless from £450/m, framed from £350/m, and external from £450/m.

Frameless glass landing balustrade with oak handrail — 90 cm height per DB-SUA Article 3.2, no climbable horizontal projections, Ø10 cm sphere rule satisfied throughout

Handrail (Pasamanos) — When Required, Height & Continuity

Handrail provisions in DB-SUA Article 4.2.4 govern when a handrail is required, on which side(s), what height it must be installed, and how it must be detailed for grip, continuity and end conditions.

When a Handrail Is Required

• All staircases of uso general — handrail mandatory on at least one side
• Staircases with anchura > 120 cm — handrail mandatory on both sides
• Accessible itineraries (staircases serving as part of an accessible route per DB-SUA Article 1.1.9) — handrail mandatory on both sides regardless of width
• Staircases with anchura > 4 m — additional intermediate handrails required, max 4 m separation between handrails
• Uso restringido (villa interior) — handrail recommended but not strictly required by code; in practice always specified

Height & Geometry

Accessible Staircases — Stricter Requirements

For staircases forming part of an itinerario accesible (accessible route), handrails have additional provisions:

• Handrail on both sides regardless of staircase width
• Two-height handrails recommended — one at 90–110 cm (standard adult), one at 65–75 cm (children, wheelchair users)
• Strong contrast between handrail and surrounding wall/balustrade
• Tactile indication at start and end of staircase (Braille or embossed signage)

Curved Staircases & Special Configurations

Curved-Tread Geometry

For curved staircases, the variable tread depth across the width creates a geometric challenge. CTE DB-SUA addresses this in Article 4.2.1.3:

• Minimum huella at narrow side: 5 cm (uso restringido) or governed by the use general formula evaluated at the measurement axis
• Maximum huella at wide side: 44 cm
• Measurement axis: at the centreline if the staircase width is <1 m; at 50 cm from the inner edge if width ≥1 m
• The ergonomic formula 54 ≤ 2C+H ≤ 70 must be satisfied at 50 cm from both extreme edges of the curved section (uso general)
• Useful width on curves: zones where the tread is <17 cm at the inner edge are excluded from the useful width calculation

For Continox spiral and curved-tread designs, this typically means the inner radius is dimensioned so that the 17 cm tread depth is achieved at a comfortable wall offset — for villa applications, this usually requires inner radius ≥40 cm depending on tread width.

Mixed Straight-Curved Flights

Where a flight transitions from straight to curved (a common configuration in U-shape staircases at a quarter or half landing), the huella measured at the staircase axis on the curved portion must be ≥ the huella on the straight portion. This prevents users from encountering a sudden shallowing of the tread at the transition point.

Spiral Staircases — Tipo Caracol

Pure spiral staircases (tipo caracol) — where every tread is curved, rotating around a central pole — are highly restricted in CTE applications:

• Permitted in uso restringido (villa interior) within geometric limits
• Permitted as escaleras de servicio (service staircases used by limited authorised personnel)
• NOT permitted as the primary staircase in uso general applications
• NOT permitted as a fire evacuation route per RD 486/97

Continox does not specify spiral staircases for villa applications because the geometric constraints rarely produce a comfortable, safe staircase by modern luxury residential standards. Our central spine systems achieve the visual lightness clients want from a "spiral" without the regulatory restrictions.

Y-shape central spine staircase — La Zagaleta-class villa specification with curved-transition flights satisfying Article 4.2.1.3 (huella ≥5 cm narrow side, ≤44 cm wide side)

Recent Updates — DB-SUA July 2024 Comments & Coming Changes

The CTE DB-SUA was significantly updated in July 2024 with new official commentary clarifying ambiguous provisions. The 15 July 2024 update is currently the operative legal reference point, supplemented by the public consultation (audiencia pública) on the Real Decreto modifying DB-SUA, which was open until 9 December 2025.

July 2024 Update — Key Clarifications

The July 2024 update did not change the dimensional limits but added official Ministry of Transport, Mobility and Urban Agenda commentary on application questions that had created interpretation disputes. Key clarifications:

• "Lift alternative" definition — for the contrahuella ≤17.5 cm rule, "lift as alternative to staircase" does not require the lift to be physically adjacent; it must merely be usable as an alternative under normal conditions
• Open-riser exemption boundary — confirmed that the Ø10 cm sphere rule does NOT apply to open-tread gaps in uso restringido staircases (subject to the 2.5 cm projection overlap)
• Curved-tread axis measurement — clarified that the 1 m width threshold for measurement-axis selection is measured perpendicular to the line of motion, not absolute
• Handrail extension at top of stairs — the 30 cm horizontal extension applies even where a wall or column makes physical extension difficult; alternative compliant detailing is required

UNE-EN 81-70:2022+A1 — Lift-Stair Coordination

From 21 February 2025, UNE-EN 81-70:2022+A1 became applicable for lifts in residential buildings. While not directly modifying DB-SUA staircase rules, it tightens the relationship between lift accessibility and staircase requirements — particularly affecting the "lift as alternative" provision discussed above.

Coming Changes — RD Modifying DB-SUA (Audiencia Until December 2025)

A Real Decreto modifying DB-SUA was in audiencia pública (public consultation) until 9 December 2025. This RD transposes EU Directive 2024/1275 (energy performance of buildings recast) and includes some accessibility-related accompanying changes. Publication of the modifying Real Decreto is expected following the conclusion of the audiencia pública review.

Key proposed changes affecting staircases:

• Strengthened accessibility requirements for renovations (obras de reforma) in residential buildings being upgraded for energy performance
• Clearer integration of staircase compliance with the Libro del Edificio (Building Logbook) requirements
• Possible introduction of mandatory two-height handrails in additional contexts

Continox monitors all CTE updates and adjusts our standard compliance schedule accordingly. Architects working with us are advised on any provisions affecting their specific project at the design phase.

Bespoke oak spine staircase with LED tread lighting — engineered to current CTE DB-SUA July 2024 update, ready for any compliance updates following the recent audiencia pública review

CTE DB-SUA vs UK Approved Document K — Comparison Table

Continox is a UK-based design studio supplying staircases across Spain. Architects sometimes ask how the Spanish CTE DB-SUA differs from the UK Approved Document K (Buildings Regulations Approved Document K — Protection from falling, collision and impact). The comparison below covers the key dimensional and detailing differences:

Key Practical Differences

For an architect transitioning from UK practice to Spanish projects, the main practical differences to internalise:

• The two-class system (uso restringido vs uso general) is cleaner than the UK's three-category system (private / utility / general access — Cat 1, 2, 3)
• The ergonomic formula is mandatory in uso general CTE applications, where the UK equivalent is recommendation only
• Spanish risers are permitted slightly higher in private dwellings (20 cm CTE vs 22 cm UK — actually CTE is stricter here)
• Spanish public stair tread is 28 cm minimum vs UK 25 cm minimum (Cat 1) — Spain is stricter
• Open risers in uso general are categorically prohibited in Spain; UK allows them under sphere-rule compliance

Premium Continox specification — UK design heritage combined with CTE DB-SUA engineering for Spanish market, manufactured at our EN 1090-1 EXC2 facility near Kraków

How Continox Engineers Staircases to CTE Compliance

Every Continox staircase supplied to Spain is engineered to satisfy CTE DB-SUA Sección 1 from the design phase. The process integrates dimensional engineering, structural calculation and documentation into a single compliance package:

Step 1 — Use Classification Confirmation

At the project enquiry stage, Continox engineers confirm with the architect of record whether the staircase is uso restringido (villa interior, single dwelling) or uso general (residential common, commercial, public). This drives all subsequent geometric decisions. See our project portfolio for completed villa and commercial examples.

Step 2 — Geometric Design

Using the project's stairwell dimensions and floor-to-floor height, our engineers calculate the optimal huella/contrahuella combination satisfying the applicable CTE requirements. For uso general projects, we deliberately design within the regla de oro 60 ≤ 2C+H ≤ 64 cm comfort range rather than just the legal 54–70 envelope.

Step 3 — Structural Calculation

All Continox staircases are structurally engineered by a UK Chartered Structural Engineer (IStructE), working to the Eurocode framework (EN 1990, EN 1991, EN 1993) which is fully recognised in Spain. The structural calculations cover:

• Variable load on treads (3.0 kN/m² residential, 4.0 kN/m² commercial)
• Concentrated point load on treads (2.0 kN at midspan)
• Horizontal balustrade line load (0.8 kN/m residential, 3.0 kN/m public concurrence)
• Frameless glass balustrade engineering per EN 14449 and EN 12150
• Connection design including substrate fixing schedule

Step 4 — Manufacturing & CE Marking

Steel components are fabricated at our EN 1090-1 EXC2 certified facility near Kraków, covering CE marking and Declaration of Performance per EU Construction Products Regulation 305/2011. Every staircase ships with the marcado CE plate fitted and the DoP packaged with the technical pack.

Step 5 — Technical Pack with CTE Compliance Schedule

Each project ships with a technical pack containing:

• 3D visualisations (DWG, PDF, STEP for BIM coordination)
• Detailed shop drawings with dimensional schedule
• Structural calculations signed by IStructE
• CTE DB-SUA compliance schedule — line-by-line confirmation of how each provision is satisfied
• CE marking documentation and Declaration of Performance
• Glass certificates (EN 14449 & EN 12150 compliance)
• Material certificates for steel and timber components

Step 6 — Liability Separation

Continox supplies components and supporting technical documentation against the architect-approved 3D design and project-supplied dimensions. Final compliance verification, Building Control acceptance and Certificado Final de Obra remain the legal responsibility of the project's Spanish-registered arquitecto director de obra and arquitecto técnico. The CTE compliance schedule provides evidence; the certifying architect signs the formal compliance statement.

FAQ — Architect Questions Answered

Reviewed by Continox Technical Team. This guide reflects CTE DB-SUA as published with comments (July 2024 update), supplemented by the public consultation that ran through 9 December 2025. We monitor all CTE updates and will revise this guide upon publication of the modifying Real Decreto.