EN ISO 13793:2001

SLOVENSKI STANDARD
01-marec-2002
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Thermal performance of buildings - Thermal design of foundations to avoid frost heave
(ISO 13793:2001)
Wärmetechnisches Verhalten von Gebäuden - Wärmetechnische Bemessung von
Gebäudegründungen zur Vermeidung von Frosthebung (ISO 13793:2001)
Performance thermique des bâtiments - Conception thermique des fondations pour éviter
les poussées dues au gel (ISO 13793:2001)
Ta slovenski standard je istoveten z: EN ISO 13793:2001
ICS:
91.120.10 Toplotna izolacija stavb Thermal insulation
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 13793
NORME EUROPÉENNE
EUROPÄISCHE NORM
March 2001
ICS 91.020; 91.120.00
English version
Thermal performance of buildings - Thermal design of
foundations to avoid frost heave (ISO 13793:2001)
Performance thermique des bâtiments - Conception Wärmetechnisches Verhalten von Gebäuden -
thermique des fondations pour éviter les poussées dues au Wärmetechnische Bemessung von Gebäudegründungen
gel (ISO 13793:2001) zur Vermeidung von Frosthebung (ISO 13793:2001)
This European Standard was approved by CEN on 7 July 2000.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2001 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 13793:2001 E
worldwide for CEN national Members.

Page 2
Contents page
Foreword 3
Introduction 4
1 Scope 5
2 Normative references 5
3 Definitions, symbols and units 6
4 Design principles 9
5 Material properties 10
6 Climatic data 11
7 Foundation depth greater than frost depth in undisturbed ground 12
8 Slab-on-ground floors for heated buildings 13
9 Suspended floors for heated buildings 21
10 Unheated buildings 26
Annex A (normative) Definition and calculation of freezing index 30
Annex B (normative) Numerical calculations 34
Annex C (normative) Design data for slab-on-ground floors based on 0 °C criterion 38
Annex D (informative) Frost susceptibility of the ground 41
Annex E (informative) Worked examples 43
Annex ZA (normative) Normative references to International Standards and
corresponding European publications 46
Annex ZB (informative) Informative references to International Standards and
corresponding European publications 47
Bibliography 48
Page 3
Foreword
The text of EN ISO 13793:2001 has been prepared by Technical Committee CEN/TC 89 "Thermal
performance of buildings and building components", the secretariat of which is held by SIS, in
collaboration with Technical Committee ISO/TC 163 "Thermal insulation".
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by September 2001, and conflicting national standards shall
be withdrawn at the latest by September 2001.
References to International Standards that have also been published as European Standards are given in
normative annex ZA, which is an integral part of this European Standard.
Annexes A, B and C form an integral part of ISO 13793. Annexes D and E are for information only.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Czech Republic,
Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway,
Portugal, Spain, Sweden, Switzerland and the United Kingdom.

Page 4
Introduction
Frost heave is the deformation of a building due to ice lenses in the ground below it, which can occur
when soil freezes under the foundations or other structural members in contact with the soil. This is
relevant to the design of building foundations in climates where the depth of penetration of frost into the
ground may exceed the minimum foundation depth necessary for structural reasons.
Not all types of soil are susceptible to frost heave (this is discussed in annex D).
The risk of frost heave can be avoided in various ways. One is to have foundations deep enough so as to
be below the frost penetration depth. Thus, special design procedures for frost heave are not necessary
for buildings with basements extending more than the frost penetration depth below ground level (except
to ensure the use of suitable backfill material that will not adfreeze to the basement wall).
Another possibility is to remove the frost-susceptible soil down to a depth below the frost penetration
depth, and replace it with material that is non-susceptible to frost before constructing the foundations.
A third option is to insulate the foundations so as to avoid frost penetrating below the foundations. In cold
climates the latter option is frequently the most economic as it allows shallower foundations, and this
standard gives methods for determining the width, depth, thermal resistance and placement of insulation
in the foundation region in order to reduce the risk of frost heave to a negligible level.
In unheated buildings the heat available from the building itself is less than with heated buildings, and
more perimeter insulation is needed to protect the foundations.
The procedures in this standard are essentially those that have been used in the Nordic countries over
many years, and have been found to be satisfactory in practice in preventing frost heave. They are based
on the results of dynamic computer calculations, which took account of the annual temperature cycle, the
heat capacity of the ground, the latent heat of freezing of water, etc., and which have been validated by
experimental data from actual constructions.
The standard is concerned with ensuring that the ground below the foundation (if frost-susceptible) does
not become frozen. In permafrost areas (annual average temperature less than 0 °C), the appropriate
design may, by contrast, be based on maintaining the ground fully frozen for the whole year. That involves
quite different solutions that are not considered in this standard.

Page 5
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
Page 6
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.

Page 7
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
b
width of ground insulation, measured from outer limit of footing m
g
b width of ground insulation at corner m
gc
b
width of ground insulation along wall m
gw
F design freezing index K·h
d
F freezing index which statistically is exceeded once in a period of n years K·h
n
H maximum frost depth in undisturbed, snow-free ground m
H foundation depth for walls m
f
H foundation depth for corners m
fc
H depth of vertical edge insulation m
v
h floor insulation position m
L length of corner insulation (measured along external surface of wall) m
c
R thermal resistance of floor construction
f
m²·K/W
(average value over the outer 1 m of floor)
R thermal resistance of vertical edge insulation m²·K/W
v
R
thermal resistance of ground insulation m²·K/W
g
R thermal resistance of ground insulation at corner m²·K/W
gc
R
thermal resistance of ground insulation along wall m²·K/W
gw
annual average external air temperature °C
e
average internal air temperature in month m °C
i,m
Page 8
a) Lightweight concrete foundation wall with b) Floor slab with edge beam
ground insulation
c) Concrete foundation wall with ground d) Concrete foundation wall with external
insulation and internal vertical edge insulation vertical edge insulation
e) Raft construction with ground insulation f) Raft construction over a bed of crushed stones
and vertical edge insulation (h < 0 in this case, so is not considered)
Key
1 Ground insulation 2 Vertical edge insulation
3 Non frost-susceptible soil 4 Bed of crush stones ventilated from inside
NOTE These are illustrations to show thermal principles and should not be considered as constructional
details.
Figure 1 - Examples of vertical edge insulation and ground insulation in foundation structures

Page 9
4 Design principles
Soil is fully frozen when all the water in it is frozen. This is assumed to have occurred when the
temperature of the soil reaches -1 °C (see annex D). The data given in clauses 8 to 10 apply when the
foundations are to be designed so that no fully frozen soil occurs below the foundation during the design
winter. Alternative data based on a criterion of 0°C are given in annex C.
This design condition may be achieved in one of four ways:
1) arranging for the foundation depth to be greater than the depth at which fully frozen soil occurs;
2) removing frost-susceptible soil from below where the foundations will be built, to the same depth as
mentioned in 1), and replacing this with well-drained material that is non-susceptible to frost;
3) insulating the foundations to reduce heat loss from the soil below the foundations so as to keep this
soil unfrozen;
4) using heat loss from the building, or special heating measures, to keep the soil below the
foundations unfrozen.
For the purposes of this standard, 1) and 2) are equivalent and are covered in clause 7. Furthermore, the
solution adopted can be a combination of 2), 3) and 4). Thus, the thickness of any layer below the
foundations that is non-susceptible to frost may be included in the foundation depth H when using this
f
standard to decide whether frost protection measures are necessary and, if so, what insulation is needed.
NOTE 1 If
...