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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

Spain sets no fixed footing depth for a house. DB-SE-C, the CTE’s foundations code, leaves depth to your geotechnical study and a sizing check (§4.2–§4.3). Width comes off a soil table, Tabla 4.4. The only fixed figures are a 0.80 m founding depth for walls and a 10 cm blinding layer.

DB-SE-C is the Documento Básico “Seguridad Estructural: Cimientos”. It is the CTE’s structural foundations document. Unlike some countries, Spain has no frost depth to dig below. Depth is set project by project. Your geotechnical study (informe geotécnico) tells you what ground you have. Then a bearing-capacity and settlement calculation sets the depth (§4.2–§4.3). Whatever that study calls for is the depth you dig to.

There is one fixed depth figure in DB-SE-C, and it trips people up. The 0.80 m minimum founding depth applies to walls only. That means retaining or basement walls. Very low walls are excepted. It is not a rule for a strip or pad footing under a house. Do not carry that 0.80 m over to an ordinary footing. It is a different rule for a different element.

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

Width comes off the table. Strip foundation width is worked out too. DB-SE-C’s admissible bearing pressure tables give the input (Tabla 4.4, for granular soils). You size the footing for your soil class and the wall load it carries (§4.3.3, with the general method in §4.2). There is no single width to print here. Read yours off the table for your ground and load.

Concrete and rebar are deferred. DB-SE-C does not state a concrete grade or a rebar cover figure. Its own text passes both to “la instrucción EHE”. That wording is stale. EHE-08 was repealed. The Código Estructural (Real Decreto 470/2021, de 29 de junio) replaced it. It has been in force since 10 November 2021. It is mandatory for every building project started on or after 10 November 2022. DB-SE-C still says “EHE”. Read every “EHE” reference in it as the Código Estructural.

We will not print a grade or a cover number here. Both are project figures under the Código Estructural. Exposure class and the reinforcement design drive them. Do not take either off a website. Check the standard, or leave it to the engineer who sized the reinforcement.

One more fixed figure: the blinding layer. DB-SE-C sets no minimum thickness for the structural footing either. That comes out of punching shear and bending design. The one fixed thickness in the document is a 10 cm minimum blinding layer (hormigón de limpieza). That is the layer poured under the footing before you build on it. It is a different thing from the footing’s own structural depth.

Work it out on site

Depth is a call from your geotechnical study. Width comes off the bearing pressure table. Once you know both, the concrete volume is just maths. It feeds straight into the calculator. Say you have 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 comes from the geotechnical study (informe geotécnico) and a bearing-capacity and settlement calculation (§4.2–§4.3). The one fixed figure, 0.80 m, is only for retaining or basement walls. Very low walls are excepted.
How wide does a strip foundation need to be?
There is no single width figure. You read it from DB-SE-C's admissible bearing pressure tables (Tabla 4.4, for granular soils). You size the footing for your soil class and the wall load it carries. Width is the result of that check, not a number printed in the document.
What concrete goes in the foundation?
DB-SE-C does not state a grade. It defers to the concrete code, which its text still calls 'la instrucción EHE'. That wording is stale. EHE-08 was repealed. The Código Estructural (Real Decreto 470/2021) replaced it. Read any 'EHE' reference in DB-SE-C as the Código Estructural.
Is there a fixed footing thickness?
Not for the structural footing itself. That comes from punching-shear and bending design, not a printed minimum. DB-SE-C has one fixed thickness figure, and it is a different thing: 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 does not give one. It is deferred to the Código Estructural, the current name for what the text still calls 'la instrucción EHE'. Check that standard directly, or leave it to the engineer who designed the reinforcement.