DB-SI: fire safety in the Spanish building code

The document is organised into six basic requirements, each developed in one section. The sections are verified in sequence, since decisions in one condition the next.

Section	Requirement	What it translates into
SI 1	Interior spread	Fire compartments, special risk rooms, reaction to fire of materials
SI 2	Exterior spread	Strips and distances on façades and roofs, party walls
SI 3	Occupant evacuation	Occupancy calculation, escape routes, number and width of exits, signage
SI 4	Fire protection systems	Provision of extinguishers, hose reels, detection, alarm, sprinklers
SI 5	Firefighter intervention	Approach roads, façade accessibility
SI 6	Structural fire resistance	R ratings required of structural elements by use and height

Three of these sections concentrate most design and cost decisions and have their own article: compartmentation and interior spread, occupant evacuation, and fire protection systems. Structural fire resistance, given its direct link with the structural package, is also covered in a dedicated article.

Almost every DB-SI requirement is modulated by three variables. The intended use of the building determines the applicable tables: residential, office, retail, educational, hospital, public assembly, car park. The built area governs compartmentation and the provision of systems. The evacuation height, measured between the exit floor and the most remote floor, progressively tightens almost everything: resistance ratings, protected stairs, systems.

This logic has a direct economic reading. Requirement steps are not continuous but staged: crossing an area or height threshold suddenly activates new obligations. At preliminary design stage, knowing those thresholds sometimes allows the design to be adjusted to stay on the lower step, with savings far exceeding the study effort.

DB-SI requirements do not form a single work package: they are spread across the whole budget. In masonry and partitions, the compartment boundary elements with their EI ratings. In joinery, fire doors and their closing hardware. In systems, the SI 4 provision, from extinguishers to sprinklers depending on the case. In the structure, the passive protection needed to reach the required R ratings: sprayed mortars, boards, intumescent paints. In façades, the reaction-to-fire conditions and the SI 2 strips, a front the pending CTE reform reinforces after the Grenfell and Campanar fires.

As an indicative order of magnitude, the set of budget items linked to the DB-SI usually sits between 3 and 7 % of the PEM (presupuesto de ejecución material, the direct construction cost) in ordinary uses, with higher values in demanding uses such as hospitals or public assembly. The breakdown and the way to trace these items are developed in the article on the cost of CTE compliance.

The first is calculating occupancy on the low side to ease evacuation: occupancy densities are those of the SI 3 table, not the developer's forecasts, and municipal technical services check this systematically. Occupancy is justified from the table, not from the intended use.

The second is resolving compartmentation on drawings and losing it on site: a compartment only exists if all its service penetrations are sealed and all its doors close. The fire-stopping package is small; forgetting it is expensive.

The third is treating industrial use with the DB-SI: industrial premises are governed by their own regulation, the RSCIEI, and the boundary between the two regimes in mixed-use buildings deserves specific analysis. The boundary is fixed when the building's uses are defined.

The fourth is ignoring the interaction with accessibility: escape routes and the accessible routes of the DB-SUA share geometry, and refuge areas link both documents. Both documents must be verified over the same routes.