1 Scope

This standard gives simplified procedures for the thermal design of building foundations so as to avoid the occurrence of frost heave.

It applies to foundations on frost-susceptible ground, and includes buildings with both slab-on-ground floors and suspended floors.

It covers heated and unheated buildings, but other situations requiring frost protection (for example roads, water pipes in the ground) are not included.

The standard is not applicable to cold stores and ice rinks.

The standard applies in climates where the annual average air temperature is above 0 °C, but does not apply in permafrost areas where the annual average air temperature is below 0 °C.

2 Normative references

This European Standard incorporates, by dated or undated references, provisions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references, the latest editions of the publication referred to applies (including amendments).

ISO 6946 Building components and building elements — Thermal resistance and thermal transmittance — Calculation method

ISO 7345 Thermal insulation — Physical quantities and definitions

ISO 10211-1 Thermal bridges in building construction — Heat flows and surface temperatures — Part 1: General calculation methods

ISO 10456 Building materials and products — Procedures for determining declared and design thermal values

3 Definitions, symbols and units

3.1 Terms and definitions

For the purposes of this standard, the terms and definitions in ISO 7345 and the following apply.

3.1.1

slab on ground floor

floor construction directly on the ground over its whole area

3.1.2

suspended floor

floor construction in which the floor is held off the ground, resulting in an air void between the floor and the ground

NOTE This air void, also called underfloor space or crawl space, may be ventilated or unventilated, and does not form part of the habitable space.

3.1.3

vertical edge insulation

insulation placed vertically against the foundation internally and/or externally, or within the foundation itself

3.1.4

ground insulation

insulation placed horizontally (or nearly so) below ground, external to the building

NOTE See Figure 1.

3.1.5

freezing index

24 times the sum of the difference between 0°C and daily mean external air temperature, accumulated on a daily basis over the freezing season (including both positive and negative differences)

3.1.6

freezing season

period during which the mean daily external air temperature remains less than 0°C, together with any freezing/thawing periods at either end of this period if they result in net freezing

3.1.7

frost depth

depth of penetration of frost into the ground

3.1.8

foundation depth

depth of foundation below the outside ground level

NOTE If the foundations are put on a layer of well-drained material that is non-susceptible to frost, the thickness of such a layer may be included in the foundation depth.

3.1.9

frost-susceptible soil

soil of a type which may cause frost heave forces when frozen as part of the ground

3.1.10

floor insulation position

height of lower surface of the floor insulation layer above external ground surface

NOTE If there is no insulation in the floor this quantity is measured from the floor surface.

3.2 Symbols and units

The following is a list of the principal symbols used. Other symbols are defined where they are used within the text.

Symbol	Quantity	Unit
B	width (smaller dimension) of building	m
bg	width of ground insulation, measured from outer limit of footing	m
bgc	width of ground insulation at corner	m
bgw	width of ground insulation along wall	m
Fd	design freezing index	K·h
Fn	freezing index which statistically is exceeded once in a period of n years	K·h
H0	maximum frost depth in undisturbed, snow-free ground	m
Hf	foundation depth for walls	m
Hfc	foundation depth for corners	m
Hv	depth of vertical edge insulation	m
H	floor insulation position	m
Lc	length of corner insulation (measured along external surface of wall)	m
Rf	thermal resistance of floor construction (average value over the outer 1 m of floor)	m2·K/W
Rv	thermal resistance of vertical edge insulation	m2·K/W
Rg	thermal resistance of ground insulation	m2·K/W
Rgc	thermal resistance of ground insulation at corner	m2·K/W
Rgw	thermal resistance of ground insulation along wall	m2·K/W
	annual average external air temperature	°C
θi,m	average internal air temperature in month m	°C

a) Lightweight concrete foundation wall with ground insulation	b) Floor slab with edge beam
c) Concrete foundation wall with ground insulation and internal vertical edge insulation	d) Concrete foundation wall with external vertical edge insulation
e) Raft construction with ground insulation and vertical edge insulation	f) Raft construction over a bed of crushed stones (h < 0 in this case, so is not considered)

Key

NOTE These are illustrations to show thermal principles and should not be considered as constructional details.