ICS 91.080  
 
Reference number  
DRS 114-3: 2020  
© RSB 2020  
  
 RWANDA 
STANDARD  DRS 
114-3  
 
Second edition  
2020 -mm-dd 
 
Structural design  — 
Part 3 : Actions on structures - Thermal 
actions  on building  
 
 DRS  114-3: 2020  
©RSB 2020  - All rights reserved                  ii 
 In order to match with technological development and to keep continuous progress in industries, 
standards are su bject to periodic review. Users shall ascertain that they are in possession of the latest 
edition  
 
 
 
 
 
 
 
 
© RSB 2020  
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized 
in any form or by any means, el ectronic or mechanical, including photocopying and microfilm, without 
prior written permission from R SB. 
Requests for permission to reproduce this document should be addressed to : 
Rwanda Standards  Board  
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KK 15 Rd, 49  
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Website: www.rsb.gov.rw  
ePortal: www.portal.rsb.gov.rw   DRS114-3: 2020  
iii                ©RSB 2020  - All rights reserved  
 Contents  Page 
Foreword  ................................ ................................ ................................ ................................ ..........................  ivv 
1 Scope  ................................ ................................ ................................ ................................ ......................  1 
2 Normative references  ................................ ................................ ................................ ............................  1 
3 Terms and definitions  ................................ ................................ ................................ ...........................  1 
4 Symbols (and abbreviated terms)  ................................ ................................ ................................ ........  2 
5 Classification of actions  ................................ ................................ ................................ .......................  3 
6 Design Situations  ................................ ................................ ................................ ................................ .. 3 
7 Representation of actions  ................................ ................................ ................................ ....................  3 
8 Temperature changes in building s ................................ ................................ ................................ ...... 4 
8.1 General  ................................ ................................ ................................ ................................ ...................  4 
8.2 Determination of temperatures  ................................ ................................ ................................ ..........  54 
8.3 Thermal cond uctivity  ................................ ................................ ................................ ..........................  65 
8.4 Thermal resistance  ................................ ................................ ................................ ................................  7 
8.4.1  Thermal resistance of homogeneous layers  ................................ ................................ ......................  7 
9 Temperature changes in industrial chimneys and tanks  ................................ ................................  98 
9.1 General  ................................ ................................ ................................ ................................ .................  98 
9.2 Temperature components  ................................ ................................ ................................ ....................  9 
9.3 Consideration of temperature components ................................ ................................ ....................  109 
9.4 Determination of temperature components  ................................ ................................ .....................  10 
9.5 Values of temperature components (indicative values)  ................................ ................................ .. 10 
Annex  A (normative)  Temperature profiles in buildings and other construction works  .........................  11 
Annex  B (informative)  Temperature profiles in buildings and other construction works  .......................  12 
 DRS  114-3: 2020  
©RSB 2020  - All rights reserved                  iv 
 Foreword   
Rwanda Standard s are prepared  by Technical Committees and approved by R wanda Standards Board (RSB) 
Board  of Directors in  accordance with the procedures of RSB, in compliance with Annex 3 of the WTO/TBT 
agreement on the preparation, adoption and application of standards.  
The main task of technical committees is to prepare national standards.  Final Draft Rwand a Standards 
adopted by Technical committ ees are ratified  by me mbers of RSB Board of Director s for publication and 
gazettment as Rwanda Standards.  
DRS 114-3 was prepared by Technical Committee RSB/TC 09, Civil Engineering and Building Materials . 
In the prep aration of this standard, reference was made to the following standard s: 
1) BS EN 1991 -1-5: 2003: Euro code 1: Actions on structures — Part 1 -5: General actions — Thermal 
actions  
2) BS EN 12524:  2000: Building materials and products − Hygrothermal properties – Tabulated design 
values.  
The assistance de rived from the above source is hereby acknowledged with thanks.  
This second  edition cancels and replaces the first  edition (RS  114-3: 2020 ), of which has been technically 
revised.  
 DRS 114 consists of the following parts, under the general title Structural Design — 
 Part 1: Actions on structures — Densities, self -weight, imposed loads for buildings  
 Part 2: Actions on structures — Wind actions  
Part 3: Thermal actions on Building  
Committee  membership  
The following organizations were represented on the Technical Committee on Civil Engineering and Building 
Materials (RSB/TC 09)  in the preparation of this standard.  
University of Rwanda – College of Science and Technology (UR -CST)  
Institut d’ E nseignement Supérieur (INES - Ruhengeri)   
City of Kigali  DRS114-3: 2020  
v                ©RSB 2020  - All rights reserved  
 Green Effect Engineering  
Integrated Polytechnic Regional Centre –Kigali (IPRC)  
NPD Ltd  
REAL Contractors Ltd  
Rwanda Housing Authority (RHA)  
Rwanda Transport Development Agency (RTDA)  
Standard For Susta inability (SFS)  
Gasabo 3D  
Masss Design Group - Rwanda  
NPD Ltd  
Enterprises -Generale -des-Constrictions - EGC  
TECOS Ltd  
Institution of Engineers Rwanda  
CIMERWA Ltd  
Rwanda Standards Board (RSB) – Secretariat  DRS  114-3: 2020  
©RSB 2020  - All rights reserved                  vi 
 Introduction   
Changes in temperatures may cause addi tional deformations and stresses and may, in some cases,  
significantly affect ultimate and serviceability limit states of structures. Fundamental principles and rules  
described in this standard provide basic tools for specifications of temperature changes and for the evaluation  
of thermal actions effects in buildings.   
Deformations and consequent stresses induced by the thermal actions are dependent on the geometry of the  
element considered and the physical properties of the materials employed in its constr uction.  
There are parameters correlated with the climate of the geographical location of the construction site and the  
consequent seasonal temperature variations. Other parameters are strictly linked to the conditions of the  
particular building in question  are the presence of other nearby structures that act as solar radiation screens,  
the building orientation, its total mass (and consequent thermal inertia), the properties of its finishing (i.e. the  
degree of their solar energy absorption and thermal isola tion) and the characteristics of the interior heating, air  
conditioning and ventilation.  DRS 114-3: 2020  
1                ©RSB 2020  - All rights reserved  
 Structural design  — Part 3: actions on structures - thermal actions  
1 Scope   
1.1 This Draft Rwanda standard gives principles and rules for calculating thermal actions o n buildings, and 
their structural elements.  
1.2 This Part describes the changes in the temperature of structural elements. Characteristic values of 
thermal actions are presented for use in the design of structures which are exposed to daily and seasonal 
climatic changes.  
1.3 This standard will be applied in accordance with Rwanda Building Control Regulations, specifically 
clauses regarding heating systems and comfort levels in buildings.  
2 Normative references   
The following documents are referred to in the t ext 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 13370 , Thermal performance of buildings — Heat transfer via the ground — Calculation methods  
RS 112, Basis of structural design  
3 Terms  and definitions   
For the purposes of this document, the following terms and definitions apply.  
3.1 
thermal actions  
thermal actions on a structure or a structural element are those actions that arise from the changes of  
temperature fields within a specifie d time interval  
3.2 
shade air temperature  
temperature measured by thermometers placed in a white painted louvred wooden box known as a   
©RSB 2020  - All rights reserved                  2 
 “Stevenson screen”  
3.3 
maximum shade air temperature Tmax 
value of maximum shade air temperature with an annual probabili ty of being exceeded of 0 .02 (equivalent to a 
mean return period of 50 years), based on the maximum hourly values recorded  
4 Symbols (and abbreviated terms)   
For the purposes of this standard, the following symbols apply.  
 R   thermal resistance of structura l element  
 U   conductance or thermal transmittance W/m2K 
 Rin   thermal resistance at the inner surface  
 Rout   thermal resistance at the outer surface  
 Rse   external surface resistance m2.K/ W  
 Rsi   internal surface resistance m2.K/ W  
 Tmax   maximum s hade air temperature with an annual probability of being exceeded of 0 .02   
   (equivalent to a mean return period of 50 years)  
 Tmin   minimum shade air temperature with an annual probability of being exceeded of 0 .02 (equivalent 
to a  mean return period of 50 years)  
 T0   initial temperature when structural element is restrained  
 Tin   air temperature of the inner environment  
 Tout   temperature of the outer environment  
 ΔTU   uniform temperature component  
 ΔTE   non-linear part of the temperature difference component  
 ΔT   sum of linear temperature difference component and non -linear part of the temperature   
   difference component  
 ΔTp   temperature difference between different parts of a structure given by the difference of    
   average  temperatures of these parts  DRS 114-3: 2020  
3                ©RSB 2020  - All rights reserved  
  h   height of the cross -section  
 p   annual probability of maximum (minimum) shade air temperature being exceeded (equivalent to 
   a mean  return period o f 1/p years)  
 αT   coefficient of linear expansion (1/°C)  
 λ   thermal conductivity . 
5 Classification of actions  
5.1 Thermal actions shall be classified as variable and indirect actions  
5.2 All values of thermal actions given in this Part are characteristic values unless  it is stated otherwise.  
5.3 Characteristic values of thermal actions as given in this part are values with an annual probability of being 
exceeded of 0 .02, unless otherwise stated, e.g. for transient design situations.  
6 Design situations  
6.1 Thermal actio ns shall be determined for each relevant design situation identified in accordance   
 with RS 112.  
 NOTE  Structures not exposed to daily and seasonal climatic and operational temperature changes may not 
 need to be considered for thermal actions.  
6.2 The elements of load bearing structures shall be checked to ensure that thermal movement will not  
 cause overstressing of the structure, either by the provision of movement joints or by including the   
 effects in the design.  
7 Representation of actions  
7.1 Daily and seasonal changes in shade air temperature, solar radiation, etc., will result in variations of the 
temperature distribution within individual elements of a structure.  
7.2 The magnitude of the thermal effects will be dependent on local climatic condit ions, together with the 
orientation of the structure, its overall mass, finishes (e.g. cladding in buildings), and in the case of building 
structures, heating and ventilation regimes and thermal insulation.  
7.3 The temperature distribution within an indivi dual structural element may be split into the following four 
essential constituent components, as illustrated in Figure 1:  
a) uniform temperature component, ΔTu ; 
b) linearly varying temperature difference component about the z-z axis, ΔTMY;  
©RSB 2020  - All rights reserved                  4 
 c) linearly varying temperature difference component about the y-y axis, ΔTMZ; 
d) non-linear temperature difference component, ΔTE. This results in a system of self -equilibrated  stresses 
which produce no net load effect on the element.  
7.4 The strains and therefore any resulting stresses are dependent on the geometry and boundary conditions 
of the element being considered and on the physical properties of the material used. When ma terials with 
different coefficients of linear expansion are used compositely the thermal effect shall be taken into account.  
 
 
    (a) Component of the uniform temperature; (b) and (c) components of the temperature linearly variable  
       according to t wo axes contained in the plan of the section; (d) a residual component  
Figure 1 — Diagrammatic representation of constituent components of a temperature profile  
 
7.5 For the purpose of deriving thermal effects, the coefficient of linear expansion for a mat erial shall be used.  
NOTE  The coefficients of linear expansion for a selection of commonly used materials are given in annex A . 
8 Temperature changes in buildings  
8.1 General  
8.1.1  Thermal actions on buildings due to climatic and operational temperature changes shall be 
considered in the design of buildings where there is a possibility of the ultimate or serviceability limit states 
being exceeded due to thermal movement and/or stresses.  
NOTE 1 Volume changes and/or stresses due to temperature changes may also be influenced by:  
a) shading of adjacent buildings,  
b) use of different materials with different thermal expansion coefficients and heat transfer,  DRS 114-3: 2020  
5                ©RSB 2020  - All rights reserved  
 c) use of different shapes of cross -section with different uniform temperature.  
NOTE 2 Moisture and other environmental f actors may also affect the volume changes of elements.  
8.2 Determination of temperatures  
8.2.1 Thermal actions on buildings due to climatic and operational temperature changes shall be 
determined in accordance with the principles and rules provided in this Sec tion taking into account national or 
regional data and experience.  
8.2.2  The climatic effects shall be determined by considering the variation of shade air temperature and 
solar radiation. Operational effects (due to heating, technological or industrial pr ocesses) shall be considered 
in accordance with the particular project.  
8.2.3  In accordance with the temperature components given in Section 7, climatic and operational thermal 
actions on a structural element shall be specified using the following basic qu antities:  
a) uniform temperature component ΔTu given by the difference between the average temperature T   
 of an element and its initial temperature T 0. 
b) linearly varying temperature component given by the difference ΔTM between the temperatures on  
 the outer and inner surfaces of a cross section,  or on the surfaces of individual layers.  
c) temperature difference ΔTp of different parts of a structure given by the difference of average       
temperatures of these parts.  
NOTE  Values of ΔTM and ΔTp may be provided for the particular project.  
8.2.4 In add ition to ΔTu, ΔTM and ΔTp, local effects of thermal actions shall be considered where relevant 
(e.g. at supports or fixings of structural and cladding elements). Adequate representation of thermal actions 
shall be defined taking into account the location o f the building and structural detailing.  
8.2.5 The uniform temperature component of a structural element ΔTu is defined as:  
ΔTu = T – T0 (1) 
where , 
 T is an average temperature of a structural element due to climatic temperatures in winter or summer season  
and due to operational temperatures.  
The quantities ∆ Tu, ∆TM, ∆Tp, and T shall be determined in accordance with the  principles provided in 8.3 
using regional data. When regional data are not available,  the rules in 8.3 may be applied.  
The first step is to  determine the value of mean temperature T. It is calculated as the value of the mean winter 
or summer temperature of the structural element in question by adopting a specific profile that defines the 
temperature distribution throughout the element’s thick ness. If the internal ( T
in) and external ( T
out) conditions  
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 are sufficiently similar, a simplified procedure can be adopted, and the mean temperature may be determined 
as  
                                                             (2) 
8.3 Thermal conductivit y 
Conductivity (λ) of a material is its ability to conduct heat through its internal structure. Conductance (U) 
[W/m²K] on the other hand is an object property and depends on both its material and thickness. Thermal 
conductivity depends on temperature, den sity and moisture content of a material. Generally light materials are  
better insulators than heavy materials, because light materials often contain air enclosures. Heat energy can 
be transferred by conduction, convection or radiation.  
8.3.1 Thermal insula tion 
Thermal insulation can refer to materials used to reduce the rate of heat transfer or the methods and 
processes used to reduce heat transfer. In thermal insulation calculations, this coefficient is used to calculate 
insulation material thickness neede d to maintain inside -outside temperature difference depending on heating 
system and insulation area. Design thermal values for materials in general building application are given in 
Table 1. 
Table 1 — Design thermal values for materials in general building  application  
Material group or application  Density ρ 
kg/m3 Design thermal 
conductivity λ 
W/(m.K)  
Asphalt  2100  0.70 
Bitumen    1050  0.20 
Concrete  
               Light weight density  
               Medium density  
 
               High density                
1800  
2000  
2200  
2400   
1.15 
1.35 
1.65 
2.00 
Floor coverings  
               Rubber  
               Plastics  
               felt  
               wool 
               cork 
               Tiles  
               Carpet/textile flooring   
1200  
1700  
12 
20 
20 
2000  
200  
0.17 
0.25 
0.05 
0.06 
0.05 
1.2 
0.06 
Gase  
               Air            
1.23  
0.025  
 
Glass  
               Soda lime   
2500   
1.00 DRS 114-3: 2020  
7                ©RSB 2020  - All rights reserved  
                Quartz  
               Glass mosaic  2200  
2000  1.40 
1.1.20  
Water at 10oC 
Water at 40oC 
Water at 80oC 1000  
990 
970 0.60 
0.63 
0.67 
Metals  
               Aluminium  
               Bronze  
               Brass  
               Copper  
               Cast iron  
               Lead  
               Steel  
               Stainless steel  
               Zinc  
2700  
8300 - 8500  
8300 - 8500  
8700 -8900  
7100 -7250  
11200 -11400  
7700 -7800  
7900  
7100 -7200   
160 
65 
120 
380 
50 
35 
50 
17 
110 
Masonry  
             Brickwork   
1700  0.73  
Wood  
            Hardwood  
            Softwood  
            Plywood  
            Hard -board  
            Soft-board   
800 
550 
700 
1000  
300  
0.17 
0.14 
0.17 
0.3 
0.08 
Tiles ( roofing)  
             Clay 
             Concrete   
2000  
2100   
1.0 
1.5 
Concrete blocks  
             Light weight  
             Medium weight  
             Heavy weight   
600 
1400  
2300   
1.63 
0.51 
0.19 
Wood - based panels  
            Plywood   
300  
0.09 
Syntheti c 
            Polyvinyl chloride (PVC)   
1400   
0.17 
NOTE  Materials are thermal insulators if their conductivity is less than 0 .065 W/m.K  
8.4 Thermal resistance  
8.4.1  Thermal resistance of homogeneous layers  
8.4.1.1  Design thermal values can be given as either design  thermal conductivity or design thermal 
resistance. If  thermal conductivity is given, obtain the thermal resistance value of the layer from   
©RSB 2020  - All rights reserved                  8 
      R= 
                                                                             ( 8.3)  
 where  
 R is the thermal resistance of the layer and is expressed in m2K/W 
 h  is the thickness of the material layer in the component and is expressed in m  
 λ is the design thermal conductivity of the material and is expressed in W/mK  
NOTE  The thickness, h, can be different from the nominal thickness (e.g. when a compressible product is installed in  
a compressed state, h is less than the nominal thickness). I f relevant, it is advisable that h also make appropriate  
allowance for thickness tolerances (e.g. when they are negative).  
8.4.1.2  Thermal resistance values used in intermediate calculations shall be calculated to at least three 
decimal  places.  
8.4.1. 3 This value is a measure of the capacity of a product to fight against heat loss . It depend s on the 
thickn ess and thermal conductivity. The highest the R , the best performing the product . 
8.4.2  Use the values in Table 2 for plane surfaces in the absence of spe cific information on the boundary 
conditions.  
8.4.2. 1 The values under “horizontal” apply to heat flow directions 30° from the horizontal plane.  
Table 2 -- Conventional surface resistances  
Surface resistance  
m2.k/W Direction of heat flow  
Upwards  Horiz ontally  Downwards  
Rsi 0.10 0.13 0.17 
Rse 0.04 0.04 0.04 
 
NOTE 1 The values given are design values. For the purposes of declaration of the  thermal transmittance of components and 
other cases where values independent of  heat flow direction are required, or when the heat flow direction is liable to vary, it is  
advisable that the values for horizontal heat flow be used.  
NOTE 2 The surface resistances apply to surfaces in contact with air. No surface  resistance applies to surfaces in contact with 
another mat erial.  
8.4.2.2  The Heat flow , going through the wall depends on temperature difference between inside and ou tside 
and thermal resistance  R of the wall.  Each element constituting the wall has thermal properties : bricks or 
concrete, insulation, rendering , etc. Wall thermal resistance is the addition of therm al resistance of each 
component  from interior coating to exte rior rendering , and superficial resistances.  DRS 114-3: 2020  
9                ©RSB 2020  - All rights reserved  
 9 Temperature changes in industrial chimneys and tanks  
9.1 General  
9.1.1  Structures which are in contact  with material with different temperatures shall be designed where 
relevant for the following conditions:  
a) thermal actions from climatic effects due to the variation of shade air temperature  and solar radiation,  
b) temperature distribution for normal and abnor mal process conditions,  
c) effects arising from interaction between the structure and its contents during  thermal changes ( e.g. 
shrinkage of the structure against stiff solid contents or  expansion of solid contents during heating or 
cooling ). 
9.1.2 The therma l stresses in the liner and in the windshield due to differences in temperature between the 
inner and outer surface of the respective walls shall be determined at the maximum flue gas temperature and 
the lowest outside temperature to be expected at site co nsidering a statistical return period of 50 years.  
9.1.3  For the purpose of verifying the thermal stability of building materials, the maximum outside 
temperature to be expected at site considering a statistical return period of 50 years has to be assumed.  
9.1.4  When  a chimney or chimney component s are restrained from adopting a distorted shape in response 
to differential expansion, resulting stresses have to be taken into account. These stresses can be high, when 
a liner or a single unlined chimney carries  flue gases from two or more sources at significant different 
temperatures or if a single side entry source introduces flue gases at very high temperatures.  
9.1.5  The liner shall be capable of expanding in both vertical and horizontal directions without an y adverse 
effect on windshield, support and liner. If a chimney has more than one liner, the individual liners shall be able 
to expand vertically and horizontally independently.  
9.1.6  The influence of the deformations of the liner support on the movements of the liner has to be taken 
into consideration.  
NOTE 1 Containment structures may be subjected to thermally induced changes in shape  arising from heating/cooling 
effects of either the contents or their surrounding external  environment.  
9.2 Temperature compone nts 
9.2.1 Shade air temperature  
9.2.1.1  Values of minimum and maximum shade air temperatures for the site location shall be obtained  from 
national maps of isotherms . 
9.2.2 Flue gas, heated liquids and heated materials temperature  
Values of maximum and mini mum flue gas, liquids and materials with different  temperatures shall be specified 
for the particular project . 
9.2.3 Element temperature   
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 The derivation of values of element temperature will depend on the material  configuration, orientation and 
location of the element and will be a function of the  maximum and minimum shade air temperature, the 
external solar radiation, and the  internal operating temperature.  
9.3 Consideration  of temperature components  
9.3.1  Both the uniform temperature component of the temperatu re distribution (see  Figure 1 (a)) and the 
linearly varying temperature difference component (see  Figure 1 (b)) shall be considered for each layer.  
9.3.2  The effect of solar radiation shall be considered in the design.  
9.3.3  This effect may be approximated  by a step temperature distribution round the  structure’s 
circumference.  
9.3.4  The uniform temperature component and the linearly varying temperature  difference component due 
to process temperature shall be considered for each layer.  
9.4 Determination  of tempe rature components  
9.4.1  The uniform and linearly varying temperature components shall be determined  taking into account 
climatic effects and operating conditions.  
9.4.2  If specific information on how the element temperature can be correlated with the  solar  radiation and 
shade air temperature is available in order to provide values of  element temperature, such information should 
be used to provide design values.  
9.4.3  Values of the uniform temperature component from heated gas flow, liquids and  heated materi als 
shall be taken from the project specification.  
9.4.4  The linearly varying temperature difference component in the wall or its layers  shall be taken as 
arising from the difference between the minimum (or maximum)  shade air temperature on the outer face  and 
the value of the liquid or gas  temperature on the inner face, taking into account insulation effects.  
9.5 Values of temperature components (indicative values)  
9.5.1  In the absence of any specific information on characteristic values of the element  tempera ture, the 
following indicative values may be used.  
NOTE  These values may be checked against any available data to ensure that they are  likely to be upper bound 
values, for the location and the type of element under consideration . 
9.5.2  Values of the maximu m and minimum uniform temperature component sh all be taken as those of the 
maximum and minimum shade air temperature (see 8.2.1).  
NOTE  The recommended value for the linear temperature difference  component is 15oC. DRS 114-3: 2020  
11                ©RSB 2020  - All rights reserved  
 Annex  A 
(normative)  
 
Temperature profiles in buil dings and other construction works  
For the determination of action effects due to temperature components, Table A.1 gives values for the 
coefficient of linear expansion for a selection of commonly used materials.   
Table A.1 — Coefficients of linear expansion  
Material  αT (x10-6/°C) 
Aluminium, aluminium alloy  24 
Stainless steel  16 
Structural steel, wrought or cast iron  12 (see Note 4)  
Concrete except as under  10 
Concrete, lightweight aggregate  7 
Masonry  6 - 10 (see Notes)  
Glass  8.5 
Timber, along grain  5 
Timber, across grain  30 - 70 (see Notes)  
NOTE 1 The values given sh all be used for the derivation of thermal actions,  unless other values can be verified by tests or more 
detailed studies.  
NOTE 2 Values for masonry will v ary depending on the type of brickwork; values  for timber across the grain can vary 
considerably according to the type of timber.  
NOTE3  For some materials such as masonry and timber other parameters (e.g.  moisture content) also need to be considered.  
NOTE 4 For composite structures the coefficient of linear expansion of the steel  component may be taken as equal to 10x10-6/oC 
to neglect restraining effects from  different αT -values.  
  
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 Annex  B 
(informative)  
 
Temperature profiles in buildings and other construction wo rks 
B.1 Temperature profiles may be determined using the thermal transmission theory.  In the case of a simple 
sandwich element (e.g. slab, wall) under the assumption that loc al thermal bridges do not exist; a temperature 
T(x) at a distance x from the inner  surface of the cross section may be determined assuming steady  thermal 
state as  
                                    (B.1)  
where:  
Tin is the air temperature of the inner environment  
Tout  is the temperature of the outer environment  
Rtot  is the total ther mal resistance of the element including resistance of both surfaces  
R(x)is the thermal resistance at the inner surface and of the element from  the inner surface up to the  point x (see Figure B.1). 
B.2 The resistance values Rtot, and R(x) [m2K/W] may be de termined using the  coefficient of heat transfer and 
coefficients of thermal conductivity given in ISO  6946:2007  and ISO 13370 (1998):  
                               (B.2)  
where:  
Rin is the thermal resistance at the inner surface [m2K/W]  
Rout  is the therm al resistance at the outer surface [m2K/W],  
λi  is the thermal conductivity and hi [m] is the thickness of the layer i, [W/(mK)]  
       (B.3)  
where layers (or part of a layer) from the inner surface up to point x (see Figure B.1) are considered only.  
NOTE  In buildings the, thermal resistance Rin = 0.10 to 0 .17 [m2K/W] (depending on the  orientation of the heat flow), 
and Rout = 0.04 (for all orientations).  DRS 114-3: 2020  
13                ©RSB 2020  - All rights reserved  
 
 
 
 
 
 
 
 
 
Key 
1 Inner surface  
2 Outer surface  
Figure B.1 — Thermal profile of a two -layer element   
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 Bibliography  
[1] BS EN 1745:  2002 Masonry and masonry products — Methods for determining design thermal values  
[2] BS EN 12939:  2001 Thermal performance of building materials  
[3] ISO 10456 Procedure for determining declared and design thermal values  
[4] www.meteorwanda.gov.rw  - Monthly weather forecast]  
        - Information on meteo stations  
 DRS 114-3: 2020  
 
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