EN ISO 13370:2017

SLOVENSKI STANDARD
01-september-2017
1DGRPHãþD
SIST EN ISO 13370:2008
7RSORWQH]QDþLOQRVWLVWDYE3UHQRVWRSORWHVNR]L]HPOMR5DþXQVNHPHWRGH,62

Thermal performance of buildings - Heat transfer via the ground - Calculation methods
(ISO 13370:2017)
Wärmetechnisches Verhalten von Gebäuden - Wärmeübertragung über das Erdreich -
Berechnungsverfahren (ISO 13370:2017)
Performance thermique des bâtiments - Transfert de chaleur par le sol - Méthodes de
calcul (ISO 13370:2017)
Ta slovenski standard je istoveten z: EN ISO 13370:2017
ICS:
91.120.10 Toplotna izolacija stavb Thermal insulation of
buildings
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 13370
EUROPEAN STANDARD
NORME EUROPÉENNE
July 2017
EUROPÄISCHE NORM
ICS 91.120.10 Supersedes EN ISO 13370:2007
English Version
Thermal performance of buildings - Heat transfer via the
ground - Calculation methods (ISO 13370:2017)
Performance thermique des bâtiments - Transfert de Wärmetechnisches Verhalten von Gebäuden -
chaleur par le sol - Méthodes de calcul (ISO Wärmeübertragung über das Erdreich -
13370:2017) Berechnungsverfahren (ISO 13370:2017)
This European Standard was approved by CEN on 27 February 2017.

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 CEN-CENELEC 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 CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2017 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 13370:2017 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 13370:2017) has been prepared by Technical Committee ISO/TC 163 "Thermal
performance and energy use in the built environment" in collaboration with Technical Committee
CEN/TC 89 “Thermal performance of buildings and building components” the secretariat of which is
held by SIS.
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 January 2018 and conflicting national standards shall
be withdrawn at the latest by January 2018.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document has been prepared under a mandate given to CEN by the European Commission and the
European Free Trade Association.
This document is part of the set of standards and accompanying technical reports on the energy
performance of buildings and has been prepared under a mandate given to CEN by the European
Commission and the European Free Trade Association (Mandate M/480, see reference [EF3] below).
Directive 2010/31/EU recasting the Directive 2002/91/EC on energy performance of buildings (EPBD,
[EF4]) promotes the improvement of the energy performance of buildings within the European Union,
taking into account all types of energy uses (heating, lighting, cooling, air conditioning, ventilation) and
outdoor climatic and local conditions, as well as indoor climate requirements and cost effectiveness
(Article 1).
The directive requires Member States to adopt measures and tools to achieve the prudent and rational
use of energy resources. In order to achieve those goals, the EPBD requires increasing energy efficiency
and the enhanced use of renewable energies in both new and existing buildings. One tool for this is the
application by Member States of minimum requirements on the energy performance of new buildings
and for existing buildings that are subject to major renovation, as well as for minimum performance
requirements for the building envelope if energy-relevant parts are replaced or retrofitted. Other tools
are energy certification of buildings, inspection of boilers and air-conditioning systems.
The use of European standards increases the accessibility, transparency and objectivity of the energy
performance assessment in the Member States facilitating the comparison of best practices and
supporting the internal market for construction products. The use of EPB standards for calculating
energy performance, as well as for energy performance certification and the inspection of heating
systems and boilers, ventilation and air-conditioning systems will reduce costs compared to developing
different standards at national level.
The first mandate to CEN to develop a set of CEN EPBD standards (M/343, [EF1]), to support the first
edition of the EPBD ([EF2]) resulted in the successful publication of all EPBD related CEN standards in
2007-2008.
Mandate M/480 was issued to review the mandate M/343 as the recast of the EPBD raised the need to
revisit the standards and reformulate and add standards so that they become on the one hand
unambiguous and compatible, and on the other hand a clear and explicit overview of the choices,
boundary conditions and input data that need to be defined at national or regional level. Such national
or regional choices remain necessary, due to differences in climate, culture and building tradition,
policy and legal frameworks. Consequently, the set of CEN EPBD standards published in 2007-2008 had
to be improved and expanded on the basis of the recast of the EPBD.
The EPB standards are flexible enough to allow for necessary national and regional differentiation and
facilitate Member States implementation and the setting of requirements by the Member States.
Further target groups are users of the voluntary common European Union certification scheme for the
energy performance of non-residential buildings (EPBD article 11.9) and any other regional (e.g. pan
European) parties wanting to motivate their assumptions by classifying the building energy
performance for a dedicated building stock.
This document supersedes EN ISO 13370:2007.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
References:
[EF1] EPBD, Directive 2002/91/EC of the European Parliament and of the Council of 16 December
2002 on the energy performance of buildings
[EF2] EPBD Mandate M/343, Mandate to CEN, CENELEC and ETSI for the elaboration and adoption of
standards for a methodology calculating the integrated energy performance of buildings and estimating
the environmental impact, in accordance with the terms set forth in Directive 2002/91/EC , 30 January
[EF3] Mandate M/480, Mandate to CEN, CENELEC and ETSI for the elaboration and adoption of
standards for a methodology calculating the integrated energy performance of buildings and promoting
the energy efficiency of buildings, in accordance with the terms set in the recast of the Directive on the
energy performance of buildings (2010/31/EU), 14 December 2010
[EF4] EPBD, Recast of the Directive on the energy performance of buildings (2010/31/EU). 14
December 2010
Endorsement notice
The text of ISO 13370:2017 has been approved by CEN as EN ISO 13370:2017 without any modification.

INTERNATIONAL ISO
STANDARD 13370
Third edition
2017-06
Thermal performance of buildings —
Heat transfer via the ground —
Calculation methods
Performance thermique des bâtiments — Transfert de chaleur par le
sol — Méthodes de calcul
Reference number
ISO 13370:2017(E)
©
ISO 2017
ISO 13370:2017(E)
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
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CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved

ISO 13370:2017(E)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols and subscripts . 3
4.1 Symbols . 3
4.2 Subscripts . 3
5 Description of the method . 4
5.1 Output . 4
5.2 General description . 4
5.3 Periodic coefficients . 5
6 Calculation of heat transfer via the ground . 5
6.1 Output data . 5
6.2 Calculation time intervals . 6
6.3 Input data . 7
6.4 Thermal properties . 7
6.4.1 Thermal properties of the ground . 7
6.4.2 Thermal properties of building materials . 8
6.4.3 Surface resistances . . 8
6.5 Internal temperature and climatic data . 8
6.5.1 Internal temperature. 8
6.5.2 Climatic data . 8
6.6 Thermal transmittance and heat flow rate . 9
6.6.1 Thermal transmittance . . 9
6.6.2 Thermal bridges at edge of floor . 9
6.6.3 Calculation of heat flow rate . 9
6.6.4 Effect of ground water . . 9
6.6.5 Special cases .10
6.7 Parameters used in the calculations .10
6.7.1 Characteristic dimension of floor .10
6.7.2 Equivalent thickness .11
7 Calculation of thermal transmittances .11
7.1 Slab-on-ground floor .11
7.2 Suspended floor .13
7.3 Heated basement .15
7.3.1 General.15
7.3.2 Basement floor .17
7.3.3 Basement walls .17
7.3.4 Heat transfer from whole basement .18
7.4 Unheated basement .18
7.5 Partly heated basement .19
7.6 Effective thermal resistance of floor construction .19
Annex A (normative) Input and method selection data sheet — Template .20
Annex B (informative) Input and method selection data sheet — Default choices .23
Annex C (normative) Calculation of ground heat flow rate .26
Annex D (normative) Slab-on-ground with edge insulation .32
Annex E (informative) Heat flow rates for edge and central regions of a building .37
Annex F (normative) Application to dynamic calculation programmes .38
ISO 13370:2017(E)
Annex G (normative) Ventilation below suspended floors .40
Annex H (normative) Periodic heat transfer coefficients .43
Bibliography .49
iv © ISO 2017 – All rights reserved

ISO 13370:2017(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www. iso. org/d irectives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www. iso. org/p atents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO’s adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: ww w .iso. org/iso / foreword. html.
ISO 13370 was prepared by ISO Technical Committee ISO/TC 163, Thermal performance and energy use
in the built environment, Subcommittee SC 2, Calculation methods, in collaboration with the European
Committee for Standardization (CEN) Technical Committee CEN/TC 89, Thermal performance of
buildings and building components, in accordance with the Agreement on technical cooperation between
ISO and CEN (Vienna Agreement).
This third edition cancels and replaces the second edition (ISO 13370:2007), which has been technically
revised.
The changes in this third edition are mostly editorial. This document has been re-drafted according to
CEN/TS 16629:2014. Some additional output variables have been introduced to facilitate the linkages
between this document and ISO 52016-1.
ISO 13370:2017(E)
Introduction
This document is part of a series aimed at the international harmonization of the methodology for
assessing the energy performance of buildings. Throughout, this series is referred to as a “set of EPB
standards”.
All EPB standards follow specific rules to ensure overall consistency, unambiguity and transparency.
All EPB standards provide a certain flexibility with regard to the methods, the required input data and
references to other EPB standards, by the introduction of a normative template in Annex A and Annex B
with informative default choices.
For the correct use of this document, a normative template is given in Annex A to specify these choices.
Informative default choices are provided in Annex B.
The main target groups for this document are architects, engineers and regulators.
Use by or for regulators: In case the document is used in the context of national or regional legal
requirements, mandatory choices may be given at national or regional level for such specific
applications. These choices (either the informative default choices from Annex B or choices adapted to
national/regional needs, but in any case following the template of Annex A) can be made available as
national annex or as separate (e.g. legal) document (national data sheet).
NOTE 1 So in this case:
— the regulators will specify the choices;
— the individual user will apply the document to assess the energy performance of a building, and thereby use
the choices made by the regulators.
Topics addressed in this document can be subject to public regulation. Public regulation on the same
topics can override the default values in Annex B. Public regulation on the same topics can even, for
certain applications, override the use of this document. Legal requirements and choices are in general
not published in standards but in legal documents. In order to avoid double publications and difficult
updating of double documents, a national annex may refer to the legal texts where national choices
have been made by public authorities. Different national annexes or national data sheets are possible,
for different applications.
It is expected, if the default values, choices and references to other EPB standards in Annex B are not
followed due to national regulations, policy or traditions, that:
— national or regional authorities prepare data sheets containing the choices and national or regional
values, according to the model in Annex A. In this case a national annex (e.g. NA) is recommended,
containing a reference to these data sheets;
— or, by default, the national standards body will consider the possibility to add or include a national
annex in agreement with the template of Annex A, in accordance to the legal documents that give
national or regional values and choices.
Further target groups are parties wanting to motivate their assumptions by classifying the building
energy performance for a dedicated building stock.
More information is provided in the Technical Report (ISO/TR 52019-2) accompanying this document.
The subset of EPB standards prepared under the responsibility of ISO/TC 163/SC 2 cover inter alia:
— calculation procedures on the overall energy use and energy performance of buildings;
— calculation procedures on the internal temperature in buildings (e.g. in case of no space heating or
cooling);
— indicators for partial EPB requirements related to thermal energy balance and fabric features;
vi © ISO 2017 – All rights reserved

ISO 13370:2017(E)
— calculation methods covering the performance and thermal, hygrothermal, solar and visual
characteristics of specific parts of the building and specific building elements and components, such
as opaque envelope elements, ground floor, windows and facades.
ISO/TC 163/SC 2 cooperates with other technical committees for the details on appliances, technical
building systems, indoor environment, etc.
This document provides the means (in part) to assess the contribution that building products and
services make to energy conservation and to the overall energy performance of buildings.
In contrast with ISO 6946, which gives the method of calculation of the thermal transmittance of
building elements in contact with the external air, this document deals with elements in thermal
contact with the ground. The division between these two International Standards is at the level of the
inside floor surface for slab-on-ground floors, suspended floors and unheated basements, and at the
level of the external ground surface for heated basements. In general, a term to allow for a thermal
bridge associated with the wall/floor junction is included when assessing the total heat loss from a
building using methods such as ISO 13789.
The calculation of heat transfer through the ground can be done by numerical calculations, which also
allow analysis of thermal bridges, including wall/floor junctions, for assessment of minimum internal
surface temperatures.
In this document, methods are provided which take account of the three-dimensional nature of the heat
flow in the ground below buildings.
Thermal transmittances of floors give useful comparative values of the insulation properties of
different floor constructions and are used in building regulations in some countries for the limitation of
heat losses through floors.
Thermal transmittance, although defined for steady-state conditions, also relates average heat flow to
average temperature difference. In the case of walls and roofs exposed to the external air, there are
daily periodic variations in heat flow into and out of storage related to daily temperature variations,
but this averages out, and the daily average heat loss can be found from the thermal transmittance
and daily average inside-to-outside temperature difference. For floors and basement walls in contact
with the ground, however, the large thermal inertia of the ground results in periodic heat flows related
to the annual cycle of internal and external temperatures. The steady-state heat flow is often a good
approximation to the average heat flow over the heating season.
In addition to the steady-state part, a detailed assessment of floor losses is obtained from annual
periodic heat transfer coefficients related to the thermal capacity of the soil, as well as its thermal
conductivity, together with the amplitude of annual variations in monthly mean temperature.
Annex F provides a method for incorporating heat transfers to and from the ground into calculations
undertaken at short time intervals (e.g. 1 h).
ISO/TR 52019-2 provides information on
— thermal properties of the ground,
— the influence of flowing ground water,
— ground floors with an embedded heating or cooling system, and
— ground floors of cold stores
along with worked examples illustrating the use of the procedures in this document.
Table 1 shows the relative position of this document within the set of EPB standards in the context of
the modular structure as set out in ISO 52000-1.
NOTE 2 In ISO/TR 52000-2, the same table can be found, with, for each module, the numbers of the relevant
EPB standards and accompanying technical reports that are published or in preparation.
ISO 13370:2017(E)
NOTE 3 The modules represent EPB standards, although one EPB standard could cover more than one module
and one module could be covered by more than one EPB standard, for instance, a simplified and a detailed method
respectively. See also Tables A.1 and B.1.
Table 1 — Position of this document (in casu M2–5) within the modular structure of the set of
EPB standards
Building
Overarching Technical building systems
(as such)
Buil
De Do ding
Hu
hu mes auto
Sub Ven mi PV,
Descrip Descrip Descrip Hea Coo mi tic Ligh ma
mo tila difi wind,
tions tions tions ting ling difi hot ting tion
dule tion ca .
ca wat and
tion
tion er cont
rol
sub1 M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11
1 General General General
Common
terms and
Building
definitions;
a
2 energy Needs
symbols,
needs
units and
subscripts
(Free)
Indoor Maximum
Applica-
3 conditions load and
tions
without power
systems
Ways to Ways to
Ways to
express express
express
4 energy energy
energy per-
perfor- perfor-
formance
mance mance
Building
Heat
categories
transfer by ISO Emission
5 and
transmis- 13370 and control
building
sion
boundaries
Building Heat trans-
occupancy fer Distribu-
6 and by infiltra- tion
operating tion and and control
conditions ventilation
Aggre-
gation of
energy Internal Storage
services heat gains and control
and energy
carriers
Building Solar Generation
zoning heat gains and control
a
The shaded modules are not applicable.
viii © ISO 2017 – All rights reserved

ISO 13370:2017(E)
Table 1 (continued)
Building
Overarching Technical building systems
(as such)
Buil
De Do ding
Hu
hu mes auto
Sub Ven mi PV,
Descrip Descrip Descrip Hea Coo mi tic Ligh ma
mo tila difi wind,
tions tions tions ting ling difi hot ting tion
dule tion ca .
ca wat and
tion
tion er cont
rol
sub1 M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11
Load
Calculated Building dispatch-
energy dynamics ing
perfor- (thermal and oper-
mance mass) ating
conditions
Measured Measured Measured
energy energy energy
perfor- perfor- perfor-
mance mance mance
11 Inspection Inspection Inspection
Ways to
express
12 BMS
indoor
comfort
External
environ-
ment
conditions
Economic
calculation
a
The shaded modules are not applicable.
INTERNATIONAL STANDARD ISO 13370:2017(E)
Thermal performance of buildings — Heat transfer via the
ground — Calculation methods
1 Scope
This document provides methods of calculation of heat transfer coefficients and heat flow rates for
building elements in thermal contact with the ground, including slab-on-ground floors, suspended
floors and basements. It applies to building elements, or parts of them, below a horizontal plane in the
bounding walls of the building situated
— at the level of the inside floor surface, for slab-on-ground floors, suspended floors and unheated
basements;
NOTE 1 In some cases, external dimension systems define the boundary at the lower surface of the floor slab.
— at the level of the external ground surface, for heated basements.
This document includes calculation of the steady-state part of the heat transfer (the annual average rate
of heat flow) and the part due to annual periodic variations in temperature (the seasonal variations of
the heat flow rate about the annual average). These seasonal variations are obtained on a monthly basis
and, except for the application to dynamic simulation programmes in Annex D, this document does not
apply to shorter periods of time.
NOTE 2 Table 1 in the Introduction shows the relative position of this document within the set of EPB
standards in the context of the modular structure as set out in ISO 52000-1.
2 Normative references
The following documents are referred to in text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 6946, Building components and building elements — Thermal resistance and thermal
transmittance — Calculation method
ISO 7345, Thermal insulation — Physical quantities and definitions
ISO 10211, Thermal bridges in building construction — Heat flows and surface temperatures — Detailed
calculations
ISO 14683, Thermal bridges in building construction — Linear thermal transmittance — Simplified
methods and default values
ISO 52000-1:2017, Energy performance of buildings — Overarching EPB assessment — Part 1: General
framework and procedures
NOTE 1 Default references to EPB standards other than ISO 52000-1 are identified by the EPB module code
number and given in Annex A (normative template in Table A.1) and Annex B (informative default choice in
Table B.1).
EXAMPLE EPB module code number: M5–5, or M5–5,1 (if module M5–5 is subdivided), or M5–5/1 (if
reference to a specific clause of the standard covering M5–5).
NOTE 2 In this document, there are no choices in references to other EPB standards. The sentence and note
above is kept to maintain uniformity between all EPB standards.
ISO 13370:2017(E)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 7345 and ISO 52000-1 and the
following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
3.1
slab on ground
floor construction directly on the ground over its whole area
3.2
suspended floor
floor construction in which the lowest floor is held off the ground, resulting in an air void between the
floor and the ground
Note 1 to entry: This air void, also called underfloor space or crawl space, may be ventilated or unventilated, and
does not form part of the habitable space.
3.3
basement
usable part of a building that is situated partly or entirely below ground level
Note 1 to entry: This space may be heated or unheated.
3.4
equivalent thickness
thickness of ground (having the thermal conductivity of the actual ground) which
has the same thermal resistance as the element under consideration
3.5
steady-state heat transfer coefficient
steady-state heat flow divided by temperature difference between internal and external environments
3.6
internal periodic heat transfer coefficient
amplitude of periodic heat flow divided by amplitude of internal temperature variation over an
annual cycle
3.7
external periodic heat transfer coefficient
amplitude of periodic heat flow divided by amplitude of external temperature over an annual cycle
3.8
characteristic dimension of floor
area of floor divided by half the perimeter of floor
3.9
phase difference
period of time between the maximum or minimum of a cyclic temperature and the consequential
maximum or minimum heat flow rate
2 © ISO 2017 – All rights reserved

ISO 13370:2017(E)
3.10
EPB standard
[6]
standard that complies with the requirements given in ISO 52000-1, CEN/TS 16628 and
[7]
CEN/TS 16629
Note 1 to entry: These three basic EPB documents were developed under a mandate given to CEN by the
European Commission and the European Free Trade Association and support essential requirements of EU
Directive 2010/31/EU on the energy performance of buildings. Several EPB standards and related documents
are developed or revised under the same mandate.
[SOURCE: ISO 52000-1:2017, 3.5.14]
4 Symbols and subscripts
4.1 Symbols
Symbol Quantity Unit
A area of floor m
B characteristic dimension of floor m
d total equivalent thickness m
z depth m
H steady-state heat transfer coefficient W/K
h height of floor surface above outside ground level m
m month number (m = 1 for January to m = 12 for December) —
P exposed perimeter m
R thermal resistance m ·K/W
U thermal transmittance between internal and external environments W/(m ·K)
z depth of basement floor below ground level m
Φ heat flow rate W
λ thermal conductivity W/(m·K)
δ periodic penetration depth m
θ temperature °C
Ψ linear thermal transmittance W/(m·K)
4.2 Subscripts
For the purposes of this document, the subscripts given in ISO 52000-1 and the following apply.
adj adjusted
an annual
b basement, below ground level; width
basement, including the effect of
bg
the ground
bsf below suspended floor
C cooling
e external
ed edge
effective (including effect of ground
eff
and/or basement)
f floor
ISO 13370:2017(E)
ground floor, including the effect of
fg
the ground
g ground
H heating
ins insulation
int internal
m month; middle (of building)
p constant pressure
pe external periodic
pi internal periodic
sog slab on ground
si internal surface
se external surface
sus suspended
unheated basement, including the
ub
effect of the ground
ve ventilation
vi virtual
w wall
wf wall/floor junction
wg wall, including the effect of the ground
combined (through walls of under-
x floor space and by ventilation of the
underfloor space)
5 Description of the method
5.1 Output
The output of this document is the thermal resistance and thermal transmittance of floors next to
the ground and basements, together with coefficients that enable heat flows to be calculated on a
monthly basis.
5.2 General description
Heat transfer via the ground is characterized by
— heat flow related to the area of the floor, depending on the construction of the floor,
— heat flow related to the perimeter of the floor, depending on thermal bridging at the edge of the
floor, and
— annual periodic heat flow, also related to the perimeter of the floor, resulting from the thermal
inertia of the ground.
The steady-state, or annual average, part of the heat transfer shall be evaluated using one of the
methods described below.
a) A full three-dimensional numerical calculation, giving the result directly for the floor concerned:
calculations shall be done in accordance with ISO 10211. The result is applicable only for the actual
floor dimensions modelled.
4 © ISO 2017 – All rights reserved

ISO 13370:2017(E)
b) A two-dimensional numerical calculation, using a floor that is infinitely long and has a width
equal to the characteristic dimension of the floor (floor area divided by half perimeter, see 6.7.1);
calculations shall be done in accordance with ISO 10211. The result is applicable to floors having
the characteristic dimension that was modelled.
NOTE 1 The largest heat flows usually occur near the edges of the floor, and in most cases only small
errors result from converting the three-dimensional problem to a two-dimensional problem in which the
width of the building is taken as the characteristic dimension of the floor.
c) The area-related heat transfer calculated by the formulae given in this document (see Clause 7),
together with the edge-related heat transfer obtained from linear thermal transmittances that are
in accordance with any of the methods in ISO 14683 (numerical method, thermal bridge catalogues,
manual calculation or default values).
NOTE 2 Linear thermal transmittance is calculated according to ISO 10211 or obtained from tables.
ISO 13789:2017, Annex A has template for identifying sources of tabulated values of linear thermal transmittance,
providing data for existing buildings, and identifying thermal bridges that can be neglected, with an informative
default choice provided in Annex B.
For c), the steady-state part of the heat transfer is given by Formula (1):
HA=⋅UP+⋅Ψ (1)
gwf
where
H is the steady-state heat transfer coefficient via the ground, in W/K;
g
A is the area of floor, in m ;
U is the thermal transmittance between internal and external environments (U , U
fg;sog fg;sus
U or U , depending on floor type; see Table 4), in W/(m ·K);
bg;eff ub
P is the exposed perimeter, in m;
Ψ is the linear thermal transmittance of the wall/floor junction, in W/(m·K).
wf
Method c) is applicable to a floor of any size or shape. U depends on floor size, but Ψ is independent
wf
of the floor dimensions. Formula (1) is modified in the case of a heated basement (see 7.3.4) and in the
case of application of Annex D (see D.1).
A template for defining whether method c) is allowed is given in Table A.2, with an informative default
choice provided in Table B.2. A template for tabulated U-values is also given in Table A.2, with an
informative default list in Table B.2.
5.3 Periodic coefficients
The document allows for different methods of allowing for phase differences between the annual cycle
of temperature variation and heat flow (see C.1).
A template for defining which method is to be used is given in Table A.3, with an informative default
choice provided in Table B.3.
6 Calculation of heat transfer via the ground
6.1 Output data
The output data are listed in Table 2.
ISO 13370:2017(E)
Table 2 — Output data
Destination mod-
Validity
Description Symbol Unit ule Varying
interval
(Table 1)
Thermal transmittance of slab on ground
U W/(m ·K) M2–5 >0 No
fg;sog
floor, including the effect of the ground
Thermal transmittance of suspended
U W/(m ·K) M2–5 >0 No
fg;sus
floor, including the effect of the ground
Thermal transmittance of wall of
heated basement, including the effect U W/(m ·K) M2–5 >0 No
wg;b
of the ground
Thermal transmittance of floor of
heated basement, including the effect U W/(m ·K) M2–5 >0 No
fg;b
of the ground
Effective thermal transmittance of
whole heated basement, inc
...