5 Material properties

5.1 Properties of the ground

The ground shall be considered to be frost-susceptible unless otherwise established by geotechnical examination.

NOTE 1 Information about frost susceptibility is given in annex D.

This standard is based on homogeneous ground consisting of frost-susceptible soil with the following properties:

thermal conductivity (unfrozen) λ = 1,5 W/(m·K)
thermal conductivity (frozen) λ_f = 2,5 W/(m·K)
heat capacity per volume (unfrozen) C =3 × 10⁶ J/(m³·K)
heat capacity per volume (frozen) C_f = 1,9 × 10⁶ J/(m³·K)
latent heat of freezing per cubic metre of soil L = 150 × 10⁶ J/m³
dry density = 1350 kg/m³
water content (saturation degree = 90 %) w = 450 kg/m³

For most types of frost-susceptible soils, the frost penetration depth adjacent to a building differs little from that determined using the above values. If, however, the actual soil properties are considerably different from those listed above, numerical calculations in accordance with annex B should be undertaken.

NOTE 2 As a general rule, the design data in clauses 8 to 10 can be applied for soils with dry density in the range 1100 kg/m³ to 1600 kg/m³ and with water saturation exceeding 80 %.

NOTE 3 When ground insulation is used, the relevant properties are those of the soil in the vicinity of the building. If ground insulation is not used, the properties of the backfill may be significant, especially if the backfill zone is relatively wide. Backfill (which is well-drained to avoid adfreezing) can increase the frost penetration depth locally due to absence of water in the soil and its associated latent heat.

5.2 Properties of building materials

For the thermal resistance of any building product, use the appropriate design value, either calculated according to ISO 10456 or obtained from tabulated values. The thermal resistance of products used below ground level shall reflect the moisture conditions of the application.

NOTE moisture conditions may be affected by whether or not the building is heated, and are often more severe adjacent to unheated buildings.

If thermal conductivity is quoted, obtain the thermal resistance as the thickness divided by thermal conductivity. The thickness used shall allow for any compression of the product, if applicable.

Ensure that any insulation material subject to compressive load has adequate compressive strength and deformation characteristics.

If ground insulation is necessary for the protection, measures shall be taken to ensure that it is not damaged or removed after completion of the building. Inform the user of the building of the presence and location of the ground insulation and of its purpose.

6 Climatic data

6.1 Design freezing index

The insulation required for frost protection depends on the severity of the design winter, expressed in terms of the freezing index together with the annual average external air temperature.

The design freezing index F_d is expressed in terms of F_n, the value of the freezing index which statistically is exceeded once in n years for the locality concerned, based on recorded meteorological data and calculated according to annex A. F_n has a 1 in n probability of being exceeded in a given winter.

Having selected the value of n, obtain F_n from tables or maps covering the locality concerned.

The appropriate value of n is related to the expected lifetime of the building and the sensitivity of the building to frost heave.

For permanent structures use F₁₀₀ or F₅₀.

NOTE For practical purposes F₁₀₀ and F₅₀ can be considered to be equivalent, as the difference between them is very small, and either may be used (depending on availability).

For the design of buildings that can tolerate some movement, or for non-permanent buildings, a lower freezing index (e.g. F₂₀, F₁₀, F₅) may be used.

6.2 Frost depth in undisturbed ground

The greatest depth of frost penetration in undisturbed ground (i.e. ground unprotected by buildings, snow cover or vegetation) depends on the climate (freezing index and annual average air temperature) and on the thermal properties of the ground.

NOTE Design values of maximum frost depth in undisturbed, homogeneous frost-susceptible ground without snow cover, H₀, may be found for some locations in national maps or tables.

If H₀ is not known, an approximate value may be calculated from the following equation:

(1)

where

F_d

is the design freezing index, in K·h;

λ_f

is the thermal conductivity of frozen soil, in W/(m·K);

is the latent heat of freezing of water in the soil per volume of soil, in J/m³;

is the heat capacity of unfrozen soil per volume, in J/(m³·K);

is the annual average external air temperature, in °C.

If appropriate soil data are not given, use the data in 5.1.

7 Foundation depth greater than frost depth in undisturbed ground

The foundations of any building can be designed so that the foundation depth, H_f, is at least the maximum frost depth in undisturbed snow-free ground, H₀.

If H_f ≥ H₀, the foundations are adequately protected against frost heave and neither edge insulation nor ground insulation is required.

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

NOTE For climates with F_d < 2000 K·h this condition applies for depth of foundation of 0,45 m or greater.

If H_f < H₀, consult clauses 8 to 10 or undertake numerical calculations according to annex B.