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Spanish Foundations: No Fixed Depth, a Table-Driven Width (CTE DB-SE-C)

Why the CTE sets no fixed foundation depth for an ordinary footing, how strip-foundation width is read off a soil-bearing table, and why concrete grade and rebar cover are deferred to the Código Estructural.

CTE DB-SE-C (RD 732/2019) Clause ES CTE DB-SE-C

The requirement

A standard shallow foundation in Spain is built to DB-SE-C, the Documento Básico “Seguridad Estructural: Cimientos” — the CTE’s structural foundations document. Before you reach for a tape, there’s a catch: DB-SE-C does not set a fixed foundation depth.

No frost-line rule, no fixed depth — for an ordinary footing. Unlike some countries, Spain has no frost-depth number to dig below. DB-SE-C §4.2–§4.3 sets the depth of a shallow foundation by the project’s geotechnical study (informe geotécnico) and a bearing-capacity/settlement calculation, not by a number printed in the document. Whatever your site investigation calls for is the depth you dig to.

There is one fixed depth figure in DB-SE-C, and it’s easy to misapply if you’re not reading closely: a 0.80 m minimum founding depth — but it applies only to walls (retaining or basement walls; the document excepts very low walls), not the general case of a strip or pad footing under a house. Don’t carry that 0.80 m figure over to an ordinary shallow footing — it’s a different rule for a different element.

12no fixed rule
CTE DB-SE-C · cimentación superficial
  1. 1 footing
  2. 2 ground

Width — read it off the table. Strip-foundation width is calculation-driven too. DB-SE-C’s admissible-bearing-pressure tables (Tabla 4.4, for granular soils) give the input; the width itself comes out as the result of sizing the footing against your soil class and the wall load it carries (§4.3.3, and the general sizing method in §4.2). There’s no single width figure to print here — read yours off the table for your ground and load.

The concrete and rebar — deferred, and the reference is stale. DB-SE-C doesn’t state a concrete grade or a rebar cover figure. Its own text defers both to what it calls “la instrucción EHE.” Here’s the catch: EHE-08 was repealed, replaced by the Código Estructural (Real Decreto 470/2021, de 29 de junio), in force since 10 November 2021 and mandatory for every building project started on or after 10 November 2022. DB-SE-C hasn’t been reworded to reflect that — every “EHE” reference in it should, in current practice, be read as the Código Estructural instead.

What we won’t print — a grade or a cover number. Both are genuinely deferred, project-specific figures under the Código Estructural, driven by exposure class and reinforcement design. Don’t take either off a website; check the standard, or leave it to the engineer who sized the reinforcement.

The one other fixed thickness figure. DB-SE-C doesn’t set a minimum structural footing thickness either — that’s a punching-shear/bending design outcome. The only fixed thickness anywhere in the document is a 10 cm minimum blinding layer (hormigón de limpieza) poured under the footing before you build on it — a different, much smaller quantity from the footing’s own structural depth.

Work it out on site

The depth is a site-investigation call, and the width comes off the bearing-pressure table — but once you know both, the concrete volume is just maths, and it feeds straight into the calculator. Say you’ve got a strip foundation to pour. These are example numbers, not code minimums — your real width and depth come off your geotechnical report and the bearing-pressure table:

  • Total length of trench: 28 m
  • Foundation width: 0.50 m (example only — read yours off the DB-SE-C bearing-pressure table for your soil class and wall load)
  • Foundation depth: 0.6 m (example only — set by your geotechnical study)

Volume = length × width × depth:

28 × 0.50 × 0.6 = 8.4 m³

So you’d order about 8.4 cubic metres, then add a bit for spillage and an uneven trench — most builders tack on 5 to 10 per cent. Swap in your own numbers and the calculator does the sum.

Do it in 5 seconds

Sources

  • CTE DB-SE-C — Seguridad Estructural: Cimientos, §4.2–§4.3 (depth and width set by geotechnical study/calculation, not a fixed figure), Tabla 4.4 (admissible bearing pressure, input to width sizing), the wall-only 0.80 m founding-depth clause, the 10 cm blinding-layer clause, and the deferral of concrete grade and rebar cover to “la instrucción EHE” (now the Código Estructural). Read it at codigotecnico.org.

Read this first. These figures are from the current DB-SE-C articulado (Real Decreto 732/2019, de 20 de diciembre). Its concrete/rebar cross-references to “la instrucción EHE” are stale — EHE-08 was repealed and replaced by the Código Estructural (Real Decreto 470/2021), mandatory for all projects started on or after 10 November 2022; read every “EHE” reference in DB-SE-C accordingly. Always confirm the current DB-SE-C text at codigotecnico.org — and get your ground checked by a geotechnical study — before you dig.

Related building rules

Frequently asked questions

Is there a minimum foundation depth in Spain?
No — not for an ordinary shallow footing. DB-SE-C sets no fixed depth and no frost-line figure; depth is set project by project from the geotechnical study (informe geotécnico) and a bearing-capacity/settlement calculation (§4.2–§4.3). The one fixed depth figure in the document is different and narrower in scope: 0.80 m minimum founding depth, but only for walls (retaining or basement walls, with an exception for very low walls) — not the general shallow-footing case.
How wide does a strip foundation need to be?
It's read off DB-SE-C's admissible bearing-pressure tables (Tabla 4.4, for granular soils) by soil class and the wall load it carries — width is an output of that calculation, not a single fixed number printed in the document.
What concrete goes in the foundation?
DB-SE-C doesn't state a grade — it defers entirely to the concrete-design code, which its own text still calls 'la instrucción EHE.' That's stale wording: EHE-08 was repealed and replaced by the Código Estructural (Real Decreto 470/2021), in force since 10 November 2021 and mandatory for every project started on or after 10 November 2022. Read any DB-SE-C reference to 'EHE' as the Código Estructural.
Is there a fixed footing thickness?
Not for the structural footing itself — that's set by punching-shear and bending design, not a printed minimum. The only fixed thickness figure in DB-SE-C is a different quantity entirely: a 10 cm minimum blinding layer (hormigón de limpieza) poured under the footing before you build on it.
What's the rebar cover?
DB-SE-C doesn't give one — it's deferred to the Código Estructural (the current name for what the document's own text still calls 'la instrucción EHE'). Check the standard directly, or leave it to the engineer who designed the reinforcement.