SIST EN ISO 13793:2002

SLOVENSKI STANDARD
SIST EN ISO 13793:2002
01-marec-2002
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GYLJDQMX]DUDGL]PU]RYDQMD,62
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
SIST EN ISO 13793:2002 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 13793:2002

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SIST EN ISO 13793:2002
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.

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SIST EN ISO 13793:2002
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EN ISO 13793:2001
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

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SIST EN ISO 13793:2002
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EN ISO 13793:2001
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.

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EN ISO 13793:2001
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.

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EN ISO 13793:2001
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

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EN ISO 13793:2001
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.

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EN ISO 13793:2001
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
0
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

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EN ISO 13793:2001
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

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EN ISO 13793:2001
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 option 4) is chosen, a combination with 3) is usually necessary to restrict heat loss.
The insulation required by options 3) and 4) can be determined by:
a) using the tables and graphical presentations in this standard (see clause 8, 9 or 10, depending on
the type of building), or
b) undertaking numerical calculations conforming with the principles given in annex B.
It is also permissible to use a combination of a) and b), for example determination of insulation required at
corners by a) and (two-dimensional) numerical calculations to determine the insulation required
elsewhere.
Heat emission from floor heating systems, heating cables in the ground, or similar, is not allowed for in
the design procedures of clauses 8 to 10. Numerical calculations shall be undertaken when such heat
emission is to be considered.
NOTE 2 If the design procedures of clauses 8 to 10 are applied to such situations, there will be
an additional margin of safety as regards frost heave, but perhaps additional heat loss.
The foundations shall be designed to avoid adfreezing of the soil, thus preventing frost heave by transfer
of shear forces, for example by having a layer of material that is non-susceptible to frost adjacent to the
walls of the foundation or basement.

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SIST EN ISO 13793:2002
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EN ISO 13793:2001
If the building envelope is not completed and/or the building is not heated before the frost season,
additional insulation measures shall be undertaken to protect the foundations.
NOTE 3 One way of achieving such additional protection is to design the foundations as for
unheated buildings using a design freezing index for non-permanent structures (see 6.1).
The parameters relevant to frost protection are:
- climate, especially freezing index and annual average temperature;
- frost susceptibility of the soil;
- thermal properties of the ground, both frozen and unfrozen;
- insulation of the floor;
- internal temperature in the building;
- the geometry, and especially the overall dimensions, of the building, and the type of foundation
used.
NOTE 4 Snow cover has the effect of reducing the frost penetration depth, but since snow cover
cannot be assured for design purposes, no allowance for it is made when assessing the design
criterion.
Some examples are illustrated in Figure 1.
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)= 1,5 W/(m·K)
thermal conductivity (frozen)= 2,5 W/(m·K)
f
6
heat capacity per volume (unfrozen) C = 3 10 J/(m³·K)
6
heat capacity per volume (frozen) C = 1,9 10 J/(m³·K)
f
6
latent heat of freezing per cubic metre of soil L = 150 10 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

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EN ISO 13793:2001
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 is expressed in terms of F , the value of the freezing index which
d n
statistically is exceeded once in n years for the locality concerned, based on recorded meteorological data
and calculated according to annex A. F has a 1 in n probability of being exceeded in a given winter.
n
Having selected the value of n, obtain F from tables or maps covering the locality concerned.
n
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 F or F .
100 50
NOTE For practical purposes F and F can be considered to be equivalent, as the difference
100 50
between them is very small, and either may be used (depending on availability).

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For the design of buildings that can tolerate some movement, or for non-permanent buildings, a lower
freezing index (e.g. F , F , F ) may be used.
20 10 5
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, H , may be found for some locations in national maps or tables.
0
If H is not known, an approximate value may be calculated from the following equation:
0
7200 F
df
H(1)
0
LCe
where
F is the design freezing index, in K·h;
d
is the thermal conductivity of frozen soil, in W/(m·K);
f
L is the latent heat of freezing of water in the soil per volume of soil, in J/m³;
C is the heat capacity of unfrozen soil per volume, in J/(m³·K);
is the annual average external air temperature, in °C.
e
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 , is at least the maximum
f
frost depth in undisturbed snow-free ground, H .
0
If H  H , the foundations are adequately protected against frost heave and neither edge insulation nor
f 0
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 < 2000 K·h this condition applies for depth of foundation of 0,45 m or
d
greater.
If H < H , consult clauses 8 to 10 or undertake numerical calculations according to annex B.
f o

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8 Slab-on-ground floors for heated buildings
8.1 Applicability
This clause applies to foundations for which H < H and to:
f 0
a) buildings in which the average internal air temperature throughout the building in each month is at
least 17 °C (i.e.  17 °C for all m);
i,m
b) buildings in which some parts are heated and some parts are unheated, provided that in the heated
parts  17 °C for all m, and that the unheated parts are treated as described in 8.5;
i,m
c) buildings in which 5 °C  < 17 °C with the modifications described in 8.8.
m
i,
If  < 5 °C in any month, the frost protection of the foundations should be designed as for unheated
i,m
buildings (see clause 10).
For data based on a design criterion of 0 °C below the foundations, see annex C.
8.2 General principles
In all cases, provide vertical edge insulation as specified in 8.6.
Heat from the building raises the ground temperature less at corners than along the sides of the building.
Therefore additional measures may be needed at corners, either by having deeper foundations at the
corners or by having additional insulation there.
This clause provides three options for achieving the necessary frost protection:
1) using vertical edge insulation only, with no ground insulation: excavate the foundations to the depth
given in 8.7.1 (a greater foundation depth is needed at corners than along the rest of the walls);
2) using ground insulation only at the corners, to avoid increasing the foundation depth at the corners:
the foundation depth is as for the walls in 1), see 8.7.2;
3) using a restricted foundation depth (not less than 0,4 m), with the same foundation depth all round
the building: provide ground insulation all round the building, but increased at the corners, see
8.7.3.
The foundation depth and/or the extent of the ground insulation is determined by the design freezing
index, F .
d
Design the floor insulation to give satisfactory floor temperatures and energy economy (i.e. independently
of the frost heave problem).
NOTE The use of vertical edge insulation and ground insulation increases floor surface
temperatures and decreases heat loss at the edge of the floor.

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8.3 Restrictions
8.3.1 Building width
The foundation depths and frost insulation specified in this clause apply to buildings with a width B of at
least 4 m.
If B < 4 m the foundations should be designed, either in depth or in provision of ground insulation,
according to the procedures given for corners, but applied all round the building.
8.3.2 Floor insulation position
The foundation depths and frost insulation specified in this clause apply to floors for which the floor
insulation position h does not exceed 0,6 m.
If h > 0,6 m, either undertake numerical calculations in accordance with annex B or use the procedures
for unheated buildings (clause 10).
8.3.3 Thermal resistance of floor slab
The thermal resistance of the floor construction, R , is the total thermal resistance between the floor
f
surface and the soil. It includes any insulation layers above, below or within it, together with that of any
floor covering.
If the thermal resistance of the floor construction varies over its area, take R as the average value over
f
the outer 1 m of floor.
The foundation depths and frost insulation specified in this clause apply to slabs with R not exceeding
f
5 m²·K/W. If R > 5 m²·K/W, either undertake numerical calculations in accordance with annex B or use
f
the procedures for unheated buildings (clause 10).
8.4 Ground insulation
Ground insulation shall be protected against risk of mechanical damage. The top surface of any ground
insulation should be at least 300 mm below ground level, unless covered by paving in which case the
depth may be reduced to 200 mm.
The data given on the width of ground insulation, b , b and b , assume that this width is measured
g gw gc
from the outermost face of the foundation.
NOTE  It may be necessary for the total width of the ground insulation to be greater than b , if
g
the footing projects beyond the foundation wall, as in Figure 1a.
If ground insulation is used together with internal edge insulation, take care to avoid a thermal bridge by
continuing the ground insulation beneath the foundation to meet the vertical edge insulation (see
Figure 1c).
Ensure that ground insulation is continuous with no gaps, that it is adequately protected from excessive
moisture by roof overhangs, sound guttering arrangements, etc. and that it is placed on a drainage layer.

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8.5 Unheated parts of a building
8.5.1 General
If some parts of a building are unheated, the procedures of 8.6 and 8.7 may be applied to the heated
parts, provided that the protection described in 8.5.2 or 8.5.3 (as appropriate) is applied to the unheated
parts of the building.
8.5.2 Building with limited unheated parts
The unheated parts of a building may be regarded as limited if their dimensions do not exceed those
L is given as a function of the design freezing index in
indicated in Figure 2, where the parameter
u
Table 1.
Table 1 - Maximum unheated length L for limited unheated parts
u
F (K·h) 30 000 > 30 000 to 40 000 > 40 000 to 50 000 > 50 000
d
L (m) 3,0 2,5 2,0 1,5
u
Key
1 Heated part
2 Unheated part
Figure 2 - Definition of limited unheated part of floor slab
NOTE L is the maximum length of an unheated part which is surrounded on three sides by
u
heated areas of the building. The maximum length is less than L in other cases, as shown in
u
Figure 2.
For limited unheated parts:
- insulate the floor of the unheated part so that the thermal resistance of the floor is at least to the
minimum ground resistance, R , for unheated buildings according to 10.2 (Table 11 or Table 12);
g
- at the external perimeter of the unheated part, use vertical edge insulation according to 8.6;

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- if the unheated part is surrounded on three sides by heated areas of the building (Figure 2a): use
frost protection as for corners according to 8.7 at the external perimeter of the unheated part and
for a distance L to each side of it, where values of L are given as a function of the design freezing
c c
index in Table 5;
- if the unheated part is surrounded on only one or two sides by heated areas of the building (Figures
2b and 2c): at the external perimeter of the unheated part and for a distance L to each side of it,
c
use ground insulation of width 0,5b , with b according to 10.2 (Table 10), of thermal resistance R
g g g
as for unheated buildings according to 10.2 (Table 1
...