KENYA STANDARD      DKS 2803:2019 
ICS  
  
 
 
  
 
  
 
 
 
  
 
  
Masonry and masonry products -  
 
Methods for determining thermal  properties  
Public Review Draft April 2019 
 
 
 
 
  
 
  
 
  
 
 
  
 
  
 
 
  
 
  
 
  
 
  DKS 2803:2019  
ii  © KEBS 2019 — All rights reserved  
 
 
  
© KEBS 2019 First Edition, 2019 
TECHNICAL COMMITTEE REPRESENTATION 
 
The following organizations were represented on the Technical C ommittee:  
 
National Housing Corporation 
Kenya Clay Products Ltd 
Coast Clay Works Ltd 
Consumer Information Network 
University of Nairobi  
Kenya Industrial Research & Development Institute 
Architectural Association of Kenya 
M&O Consulting Engineers 
Kenya Association of Manufacturers, 
Kenya National Federation of Jua Kali Association 
Lake Basin Development Authority 
Kenya Bureau of Standards — Secretariat 
 
 
 
 
 
 
 
 
 
 
 
 
  
REVISION OF KENYA STANDARDS 
 
In order to keep abreast of progress in industry, Kenya Standar ds shall be regularly reviewed. Suggestions for 
improvements to published standards, addressed to the Managing Director, Kenya Bureau of Standards, are 
welcome. 
  
 
 
© Kenya Bureau of Standards, 2017 
 
Copyright. Users are reminded that by virtue of Section 25 of the Copyright Act, Cap. 130 of 2001 of the Laws of Kenya, copyrig ht subsists 
in all Kenya Standards and except as provided under Section 25 of this Act, no Kenya Standard produced by Kenya Bureau of Stand ards 
may be reproduced, stored in a retrieval system in any form or transmitted by any means without prior permission in writing fro m the 
Managing Director.   KENYA STANDARD                                       DKS 2803:2019 
ICS  
© KEBS 2019 — All ri ghts reserved   iii Masonry and masonry products - 
 
Methods for determining thermal  properties 
 
 
 
  
 
  
 
  
 
  
 
  
 
  
 
 
  
 
  
 
  
 
  
 
  
 
  
 
   
 
KENYA BUREAU OF S TANDARDS (KEBS) 
 
Head Office: P.O. Box 54974, Nairobi-00200, Tel.: (+254 020) 605490, 602350,  Fax: (+254 020) 604031 
E-Mail: info@kebs.org, Web:http://www.kebs.org  
 
Coast Region    Lake Region    Rift Valley Region  
P.O. Box 99376, Mombasa-80100  P.O. Box 2949, Kisumu-40100   P. O. Box 2138, Nakuru-20100 
Tel.: (+254 041) 229563, 230939/40 Tel.: (+254 057) 235 49, 22396  Tel.: (+254 051) 210553, 210555  
Fax: (+254 041) 229448   Fax: (+254 057) 21814 DKS 2803:2019  
iv  © KEBS 2019 — All rights reserved  
Foreword 
 
This Kenya Standard was prepared by the Clay and Clay Products Technical Committee under the guidance 
of the Standards Projects Committ ee and in accordance with the procedures of the Kenya Bureau of 
Standards. 
 During the development of this standard, reference was made to the following documents: 
 
BS EN 1745:2012 Masonry and Masonry Products – Methods of deter mining thermal properties. 
 
Acknowledgement is hereby made for the assistance received from  these sources. 
 
  
 
  
 
 
  
 
  
 
  
 
  
 
  
 
  
 
 
  
 
  
 
  
 
  
 
  
 
  
 
   KENYA STANDARD                                       DKS 2803:2019 
ICS  
© KEBS 2019 — All rights reserved   v Introduction 
 
This Kenyan Standard provides rules for the determination of dr y and design thermal conductivity and thermal 
resistance values of masonry products and masonry.  
It describes how dry thermal values are determined. It also des cribes the correction methods to derive design 
values from a dry value. The dry value is a characteristic of a  masonry material, masonry unit or of masonry. 
On the basis of dry thermal conductivity values determination m ethods of design thermal values are given. 
 
ג10,dry,unit ) of solid 
masonry units are described and five procedures (model P1 - P5)  for the determination of equivalent dry 
ג10,dry,mat ) of masonry units with formed voids and composite masonry unit s are 
described, see Figure 1. 
 
For mortars according to EN 998-1 and EN 998-2, the models S1 -  S2 can be used. 
 Additionally three procedures for the determination of thermal resistance are described. These procedures 
are: 
 
- the use of tabulated R-values; 
- the measurement of R-value;  - the numerical calculation of R-value. 
The following major types of masonry units are covered by thisK enyan Standard: 
 
- solid masonry units; 
- masonry units with formed voids; 
- composite masonry units. 
In Figure 1, the different model s and procedures are illustrate d. 
 
The design value of a product characteristic is the value deter mined for a specific application and for use in 
calculations. 
 
Design thermal values are determined, according to the procedur e given in this Kenyan Standard according 
to the intended application, environmental and climatic conditi ons,  bearing in  mind the purpose of this 
determination, such as: 
 
- energy consumption; 
- design of heating and cooling equipment; - surface temperature determination; 
- compliance with national building regulations; - consideration of non-steady state thermal conditions in build ings. 
   
 
 DKS 2803:2019  
vi  © KEBS 2019 — All rights reserved 
 
KENYA STANDARD        DKS 2803:2019 
 
 
© KEBS 2019 — All rights reserved   1  
Masonry and masonry products - 
 
Methods for determining thermal  properties 
 
1. Scope  
 
This Kenyan Standard specifies procedures for the determination  of thermal properties of masonry and 
masonry products. 
 
 
2. Normative references 
 
The following documents, in whole or in part, are normatively r eferenced in this document and are 
indispensable for its application. For dated references, only t he edition cited applies. For undated references, 
the latest edition of the refer enced document (including any am endments) applies. 
 EN 772-4, Methods of test for masonry units -   Part 4: Determi nation of real and bulk density and of total and 
open porosity for natural stone masonry units 
 DKS 2802-7, Methods of test for masonry units -   Part 13: Dete rmination of net and gross dry density of 
masonry units (except for natural stone) 
 EN 1015-10, Methods of test for mortar for masonry -   Part 10:  Determination of dry b ulk density of hardened 
mortar 
 
EN 1934,  Thermal performance  of  buildings  -    Determinatio n  of  thermal  resistance by  hot  box method 
using heat flow meter -   Masonry 
 
EN 1936, Natural stone test methods -   Determination of real d ensity and apparent density, and of total and 
open porosity 
 
EN 12664,  Thermal performances of building materials and produ cts -    Determination of thermal resistance 
by means of guarded hot plate and heat flow meter methods -   O ry and moist products of medium and low 
thermal resistance 
 EN ISO 6946:2007, Building components and building elements -    Thermal resistance and thermal 
transmittance -   Calculation method (ISO 6946:2007) 
 EN ISO 7345:1995, Thermal insulation -   Physical quantities an d definitions (ISO 7345:1987) 
 
EN ISO 10211,   Thermal bridges in building construction -   He at flows and surface temperatures - Detailed 
calculations (ISO 10211) 
 
EN ISO 10456, Building materials and products -    Hydrothermal  properties -    T abulated design values and 
procedures for determining declared and design thermal values ( ISO 10456) 
 
3. Terms, definitions and symbols 
 
For the purposes of this document, the following terms,   defin itions   and symbols and those given in 
EN ISO 7345: 1995 apply. 
  
 
  
2  © KEBS 2019 — All rights reserved 3.1. Terms and definitions 
 
3.1.1.  masonry 
Assemblage of masonry units laid in a specified pattern and joi ned together with masonry mortar  
 
3.1.2.  masonry product 
Masonry units, masonry mortars, rendering and plastering mortar s 
 
3.1.3.  solid masonry unit 
Masonry unit containing no perforations except external indenta tions such as grip h oles grooves, etc. 
 
3.1.4.  masonry unit with formed voids 
Masonry unit with a system of intentionally formed voids 
 
3.1.5.  Composite masonry unit 
Masonry unit incorporating one or more layers of additional mat erial to enhance performance 
 
3.1.6.  thermal value 
common term for either the thermal conductivity [W/(mꞏK)] or th e thermal resistance [m2·K/W] 
 
3.1.7.  dry state 
state after drying under conditi ons stated in the relevant stan dards 
 
3.1.8. dry thermal value 
value of a thermal property of a building material or product i n a dry state determined according to this 
Kenyan Standard as a basis for the calculation of design therma l values 
 Note 1 to entry: The dry thermal value can be expressed as ther mal conductivity or thermal resistance. 
 
3.1.9.  design thermal value 
value of a  thermal property of a building material or product under specific external and internal conditions 
which can be considered as typical of the performance of that m aterial or product when incorporated in a 
building component or building 
 
3.1.10. masonry thermal conductivity 
value which is derived by dividing the thickness of a given mas onry element by its thermal resistance excluding 
surface resistance.  
3.1.11. reference conditions 
set of conditions identifying a state of equilibrium selected a s the base to which the thermal values of building 
materials and products are referred 
 
3.1.12. equivalent thermal conductivity 
value derived by dividing the width of a masonry unit with form ed voids or a composite masonry unit or masonry 
by its thermal resistance excluding surface resistance 
                                                                                                                                                                                                  
 
 
  
 
  
 
  
 
  
3.2   Symbols DKS 2803:2019  
© KEBS 2019 — All rights reserved   3  
The order of the indices for ther mal values is temperature, con dition and subject 
 
 
 
 
 
4  © KEBS 2019 — All rights reserved  
 
3.2. Subscripts 
 10           average test temperature of 10 °C 
dry         state after drying under conventional conditions as st ated in the relevant standards     
mas       masonry 
mat        material 
mor       mortar  
unit        masonry unit  
 
 
  
 
  
 
  
 
  
 
  
 
  
                                                                                                                                                                                                 
DKS 2803:2019  
© KEBS 2019 — All rights reserved   5 4. Procedures to determine ג10,dry, unit  - values for solid  masonry units and ג10,dry,mor -
Values  for mortars 
 
4.1. General 
 
ג10,dry,mor ג10,dry,mat 
ג10,dry,mat -values of solid  masonry  units  and  of  mortars   can  be  d etermined   from   tests 
10,dry,mat  to density  or 
from determining   the  thermal   transmittance   ( Umas)   of  masonry   built  from  masonry  units  and  mortar.   
ג10, dry,mat  -value is to be representative   of the material. 
 
4.2. ג10,dry, mat  -values for solid  masonry units  and mortars 
 
4.2.1.  Model S1. Determination of ג10,dry,unit   - values from tabulated ג10,dry,mat /net  dry density  
relation 
 
ג10,dry,mat -values for  different   materials   used  for  masonry   produ cts   are  given  in Annex  A, 
differentiated by material  and  dry  density.   This annex   a lso contains   values   for the water   vapour diffusion 
coefficient,   the specific heat capacity and the moisture conv ersion coefficient. 
 
These  tabulated    values  are valid  for materials  where  there  is factory  production   control  of the  net dry 
ג10,dry,mat  -values  are given  as 50% and 90 % fractiles  ( P). 
 
4.2.2.  Model S2. Determination of ג10,dry,unit  – values based on ג10,dry,mat  /net  dry density curve  
 
 
4.2.2.1.   General 
 
ג10,dry,mat   ג10,dry,mat /net  dry  density   relationship   the  following   procedure 
shall be used: 
 
4.2.2.2.  Test specimens 
 
Test specimens   shall be in accordance   with the requirements    of EN 12664.  Care should be taken that the 
test specimens   are representative   of the masonry product it self. 
 NOTE: An appropriate way to ensure this is to cut specimens fro m masonry units. 
 
4.2.2.3. Conditioning of specimens 
 Normally   masonry   materials   are tested in a dry condition.     It is   also possible to  carry out tests in a moist 
condition   (e.g.  conditioned   to constant   mass  in an envi ronment   of (23 ± 2) °C  and 50% ± 5% relative  
humidity),   in  which  case  the  measured   value  has  to  b e converted   to the  dry  state  following one of 
the procedures   given  in Clause  6. 
 
4.2.2.4. Test measurement 
 
The reference test method is given in EN 12664. The test shall be carried out at a mean temperature of 10 °C. 
 Alternative test   methods,   which   may   require   different    test   specimens    and   different   conditioning 
methods,   may  be  used,   if  the  correlation    between   t he  reference   test  method   and  the  alternative 
method  can be given.   
  
6  © KEBS 2019 — All rights reserved 4.2.2.5.  Establishing a product related ג10,dry,mat  /net dry density-curve 
 
Three items of information are necessary for this determination  procedure: 
 
ג10,dry,mat  /net dry density-correlation for  the given material (see Annex A); 
2) the product net dry density range, which can be derived eith er from the production history or 
from the net dry density tolerances which are given in the rele vant product standards; 
 
i,    on material which 
is representative for the current material produced. The measur ements of net dry density 
shall be carried out on the same specimens. The three tests ha ve to be carried out on 
specimens from different production batches to represent the ma nufactured product net dry 
density range.  These  three  measurements  are  used to  deter mine  the  distance  of  the 
ג10,dry,mat  /net  dry  density-curve,  for  a  defined  production,   from  the tabulated 
ג10,dry,mat  /net dry density curve. 
 
i -value as prescribed in 4.2.2.1   to 4.2.2.3 and calculate the  arithmetic mean value 
i -results. 
 
Measure the net dry density of each of the three samples follow ing the procedure prescribed in EN 772-4 or 
DKS 2802-7 or EN 1015-10 and calculate the arithmetic mean valu e of the 3 results. 
 
Then use the following procedure.  
net dry 
ג10,dry,mat  ג  -
and net dry density-values for the product (material) given in Annex A. 
 
value of the product from the average net dry density. Derive the upper and lower limit 
values  as  the  values  that  represent  90%  and  10%  of  th e  manufactured  product  under consideration 
density range with a confidence level of 90% according to EN IS O 10456. 
 
ג10,dry,mat  ג10,dry,mat- value related to the 
mean net dry density the manufacturer is confident to achieve. 
 
ג10,dry,unit  ג10,dry,mor  -values for mortars as the mean 
ג10,dry,mat  -value together with the difference between the limit and the m ean value.  
 
Figure 2 shows this process in the form of a graph.  
  
 
  
 
  
 
  
 DKS 2803:2019  
© KEBS 2019 — All rights reserved   7  
 
 NOTE: For factory production control purposes thermal conducti vity may be controlled from the net dry density 
of the material, see Annex E. 
 
  
 
  
 
 
 
8  © KEBS 2019 — All rights reserved 4.2.3.   Model S3. Procedures to determine ג10,dry,unit -values  from determining the thermal 
transmittance( Umas)  of masonry built from solid masonry units and mortar 
 
ג10,dry,unit -values from test measurements of the thermal transmittance of masonry built from 
masonry units and mortars, the procedure in 5.3.3 shall  be use d.  
 
4.3. Test methods and numbers of samples to be taken  for the d ifferent models 
 
In the following table test methods and numbers of samples to b e taken for the different models is given. 
 
Table 1 -   Test methods and minimum numbers of specimens withi n the test 
Test methods Minimum numbers  
of specimens 
 
Model S1:  Material density, DKS 2802-7 or EN 1936 (natural stone units)  6 
 Model S2: 
 
Material density, DKS 2802-7, EN 1015-10 or EN 1936 (natural  
3 stone units)  
Thermal conductivity, EN 12664                                                       3
 
Model S3: 
 
Gross dry density, DKS 2802-7, EN 1015-10 or EN 1936 (natural  
3 x 6 stone units)  
Thermal transmittance, EN 1934                                                      
 
  
 
6 
 
 
  
3 
  
3 
  
 
3X6 
  
3 
 
 
5. Procedures to determine equivalentג10,dry,unit ꞏvalues  for masonry units with 
formed voids and composite masonry units 
 
5.1. General  
ג10,dry,mat  
-value    of the material, there is also a high infl uence from the shape and the geometry of the voids  in  the  
unit.  The  thermal  conductivity  of  the  materials  can  be  derived  from  tables  or measurements. 
 
ג10,dry,unit - values     of masonry units wit h formed voids can be determin ed: 
 
- from tables; 
- from calculations; 
- from test measurements carried out on masonry samples. 
ג10,dry,unit - values of composite masonry units can be determined: 
 
- from calculations; 
- from measurements carried out on masonry samples.  DKS 2803:2019  
© KEBS 2019 — All rights reserved   9  
 
 
5.2. Calculation methods 
 
There are several different numerical methods in use (e.g. Fini te Difference, Finite Element) for the calculation 
of the thermal properties of masonry units with formed voids or  composite masonry units. The thermal 
conductivities of the materials and the configuration of the un its are necessary input parameters for such 
calculations. 
 
The requirements for appropriate calculation programs (accuracy , boundary conditions, etc.) are given in 
Annex D. 
 
The method described in EN ISO 6946 may also be used.  
 
5.3. ג10,dry,unit - values    of masonry units 
 
5.3.1. Determination of ג10,dry,unit - values    from tabulated גunit /גmat relation 
 
5.3.1.1. General 
 
ג10,dry,unit -values  used for masonry units with different void patterns ar e given in Annex B. Annex C provides 
an example of how to use Annex B. 
 No tabulated values for composite masonry units are given in An nex B. 
 
NOTE: The types of units shown and the pattern of voids are int ended as examples of units typically found on 
the market. They are not intended to cover every size and type of unit or void pattern produced. 
 
5.3.1.2. Application of Annex B 
 
ג10,dry,unit -values  of masonry units with formed voids given in Annex B, a re differentiated by: 
 
- material; 
- geometry of the units and geometry of formed voids; 
value of the material of the masonry units; 
Linear interpolation may be used  for material conductivities be tween the values given in the tables in 
Annex B.  
 
5.3.1.3. Model P1. The determination of the ג10,dry,unit -v a l u e    u s i n g  A n n e x  B  u s i n g  
measured thermal conductivity of the masonry unit material 
 
ג10,dry,unit -value   from  using Annex  B using measured  thermal  co nductivity  of the masonry 
unit material, the following procedure shall be used: 
 
ג10,dry,unit -value  as the value given  in the relevant 
ג10,dry,matג10,dry,mat -value is a measured 
thermal conductivity of the masonr y unit material as specified in 4.2.2. 
  
10  © KEBS 2019 — All rights reserved 5.3.1.4. Model P2. The determination of the ג10,dry,unit -value   using  Annex B using 
tabulated value from Annex A 
 
ג10,dry,unit -value     from using Annex B using tabulated value from Annex A, the following 
procedure shall be used:  
 
ג10,dry,unit -value as the value  given  in the relevant 
ג10,dry,matג10,dry,mat -value  is a tabulated 
value from Annex A. 
 
5.3.2. Determination of ג10,dry,unit -values based on calculation 
 
5.3.2.1.  General 
 
ג10,dry,unit -value    for a  masonry unit by calculation   methods followin g 5.2,  the following 
procedure shall be used: 
 Based on: 
 
- the geometry of the units; 
- the geometry of formed voids; 
ג10,dry,mat -Value; 
- the orientation of the unit in use 
a numerical model of the unit can be established and the therma l transmittance can be approximated. This  
method  is  also  suitable  for  composite  masonry  units,  wh ere  the  calculation  is  dealt  with separately for 
each layer.  
5.3.2.2. Model P3. Determination of ג10,dry,unit -values using measured thermal 
conductivity of the masonry unit material 
 
ג10,dry,unitג10,dry,mat -value the manufacturer is 
 ג10,dry,mat -value  is a measured thermal conductivity of the masonry unit material 
as specified in 4.2.2. 
 
5.3.2.3. Model P4. Determination of ג10,dry,unit -values   using tabulated value from 
Annex A 
ג10,dry,unitג10,dry,mat -value the manufacturer is 
ג10,dry,mat -value  is tabulated values from Annex A. 
5.3.3.   Model P5. Determination of ג10,dry,unit -values   from determining the thermal 
transmittance ( Umas) of masonry built from masonry units with formed voids or comp osite 
masonry units and mortar 
 
5.3.3.1. General 
 
ג10,dry,unit -values from test measurements of the thermal transmittance of masonry built from 
masonry units and mortars, the following procedure shall be use d. 
 DKS 2803:2019  
© KEBS 2019 — All rights reserved   11 5.3.3.2. Testing procedure 
 
- Select test samples from 3 different production batches for t he product under consideration. 
Determine their mean gross dry density. 
 
- From each of these batches erect one wall.  
 
- Measure   the thermal   transmittance    on each of those wal ls following   EN 1934.    If  the  
measured wall  is not  in a dry  state,   the  measured   value   has to  be converted   to the  dry  state  
following   the procedu re  given  in Clause  6. 
 
5.3.3.3. The  determination   of the  ג10,dry,unit -value 
 
 
 
The thermal conductivity of the mortar joints shall take into a ccount mortar pockets and strip bedding and the 
use of insulating material between the strips. 
 
If the units are intended to be used with unfilled vertical mor tar joints the masonry tested shall also be with 
ג10,dry,unit -values      for the units will take into account the effect of  the unfilled joints 
calculated according to EN 6946. 
 
ג10,dry,unit -values and calculate  the arithmetic mean value. 
 
Measure the gross dry density of each of the three samples take n from each batch of masonry units and mortar 
following the procedure prescribed in EN 772-4 or EN DKS 2802-7  or EN 1015-10 and calculate the arithmetic 
mean value of the 3 results. 
 
ג10,dry,mat -values  in the relevant table in Annex B find the correspondin g net dry densities values 
in Annex A.  From the corresponding net dry density values calc ulate the related gross dry density values 
using the following equation: 
 
12  © KEBS 2019 — All rights reserved  
 
 
gross dry density-
ג10,dry,unit - /gross  dry density-curve  obtained from  plotting the tabula ted 
ג10,dry,unit -values in Annex B and the corresponding calculated gross dry d ensity-values for the product. 
 
ג10,dry,unitג10,dry,unit -value     related to 
the mean gross dry density the manufacturer is confident to ach ieve. 
 Figure 3 shows this process  in the form of a graph. 
 
 
DKS 2803:2019  
© KEBS 2019 — All rights reserved   13  
 
NOTE:         For factory production control purposes thermal c onductivity may be controlled from the gross dry 
density of the product, see Annex E. 
  
 
 
  
 
 
  
 
 
14  © KEBS 2019 — All rights reserved 5.4. Test methods  and numbers  o f samples to be taken for the different models 
 In the following table test methods and numbers of samples to b e taken for the different models is given. 
 
Table 2 -   Test methods and minimum numbers of specimens withi n the test 
Test methods Minimum numbers  of specimens 
Model P1: 
 
Material density, DKS 2802-7                       
Thermal conductivity, EN 12664               
 Model P2: 
 
Material density, DKS 2802-7                       
Model P3: 
 Material density, DKS 2802-7                      
 
Thermal conductivity, EN 12664                
Model P4: 
 Material density, DKS 2802-7                      
 
Model P5:  
Gross dry density, DKS 2802-7 and            
EN 1015-10 
 
Thermal transmittance, EN ISO 1934         
6 
 
3 
 
  
 
6 
 
 
 
3 
 
3 
 
 
 
6 
 
  
3X6 
 
 
3 
 
6. Moisture conversion 
 
Design thermal conductivity values/resistance values for masonr y units or mortars may be determined using 
one of the following 3 procedures:  
ג10,dryגdesign -value  using  the  moisture  conversion 
coefficient given in Annex A for each material and the design m oisture content from the tables in EN ISO 10456 
or the nationally given design moisture content for a specific material and application. 
 Alternatively, moisture conversion coefficients and moisture co nversion factors can be derived from tests, 
carried out at several practical moisture contents. 
 
  
 
 
  
 
  
 
  
 
 DKS 2803:2019  
© KEBS 2019 — All rights reserved   15 Procedure 1 (for materials, mortar and solid masonry units):  
 
 Procedure 2 (for masonry units with formed voids and composite  masonry units): 
 Moisture   conversion   has  to  be carried   out  for  the  th ermal   conductivity   of each  constituent   material 
according  to procedure   1,  followed  by a calculation   of t he thermal  conductivity   of the  unit according  to 
5.2. 
 
For  composite   masonry   units  and  partially   filled  unit s  with  formed   voids  the  moisture   conversion 
factors  of each material  have to be taken  into account. 
 
Procedure 3 (for masonry units with formed voids): 
 
As an alternative   to proc edure   2 an approximate   method taking into account the perce ntage of voids can 
be used.   Details of this procedure can be found in informativ e Annex F. 
 
 
7. Procedures to determine design thermal values ( Rdesign,mas  or גdesign,mas ) for 
masonry built from masonry units and mortar 
 
7.1. General                                                                                                                                                     0 
 
Design thermal resistance   or design thermal   conductivity   for masonry may be determined   using   one of 
following procedures. 
 
The  Rdesign,mas  – values or גdesign,mas -values of masonry  built from  masonry  units  can be determin ed   
from calculations,   from  tables  or from tests. 
  
7.2. 
Rdesign,mas – or גdesign,mas -values based  on calculation 
 
7.2.1.  Rdesign,mas – or גdesign,mas -values based  on  גdesign -values for  the  masonry  units  and 
the mortar 
 
Determine the Rdesign,mas – or גdesign,mas –values    according  to th e following  p rocedure:  
 
 
גdesign,mas –Values  using the equation: 
 
 
 
 
7.2.2.   Rdesign,mas – or גdesign,mas -values  using a  numerical  calculation method  based on the 
design thermal conductivity of the materials used 
 
There are several numerical methods in use (e.g. Finite Differe nce, Finite Element) for the calculation of the 
thermal properties of masonry units. The thermal conductivities  of the materials as necessary input parameters 
for such calculations shall be the design,mas -value for the maso nry product used. 
 
The requirements for appropriate calculation programs (accuracy , boundary conditions, etc.) are given in 
Annex D. 
 
The method described in EN ISO 6946 may also be used.  
 
7.3.  
Rdesign,mas – or גdesign,mas -values of masonry built from masonry units with formed voids o r 
composite masonry units and mortar based  on tabulated values 
 
7.3.1.   Tabulated values 
ג10,dry,mas -values  for masonry built  with units having different void pa tterns are given in Annex B. 
 
No tabulated values for composite masonry units are given in An nex B. 
 
NOTE: The types of units shown and the pattern of voids are int ended as examples of units typically found on 
the market. They are not intend ed to cover every size and type of unit or void pattern produced. 
 
7.3.2.  Application of Annex B 
ג10,dry,mat -valuesfor the determination of Rdesign,mas – or גdesign,mas -values  of 
masonry built from masonry units with formed voids are given in  Annex B, differentiated by: 
 
- material; - geometry of the units and geometry of formed voids; 
DKS 2803:2019  
ג10,dry,mat -value of the material of the masonry units; 
ג10,dry,mor -value of the mortar.  
 
The tabulated Rdry,mas – or גdry,mas -Rdry,mas-  or Arn,dry,mas-values  should be taken as the basis for the 
calculation of any national design  values, which  are  depende nt on the  climatic  conditions and  corrections 
for  the application using Clause 6. 
 
Linear interpolation may be used  for material conductivities be tween the values given in the tables in 
Annex B.  
 
7.3.3.  Alternative application of Annex B  
 The tabulated values have been calculated assuming a specific h eight and length of the masonry units, a 
specific thickness of the horizontal mortar joints and no morta r in the vertical joints (the "basic dimensions" are 
given for each geometry class). For masonry built from units wi th a different height, a correction for the mortar 
joints may be taken into account as follows. The same procedure  may be used to determine values for masonry 
with vertical mortar joints in those cases where no separate va lues are given. These methods are suitable for 
all available masonry units. 
 
Calculate the U
masגmas-value of the masonry in the table using the equation: 
  
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A similar calculation may be applied for different length of ma sonry units and thickness of vertical mortar joints. 
 If there are no vertical mortar joints the differing lengths of  the units may be ignored. 
 
NOTE 1 The thermal transmittance of masonry made from masonry u nits with a length > 250 mm which have 
a tongue and groove system instead of vertical mortar joints wi ll be lower than the tabulated value, which 
means that the tabulated value is on the safe side. For masonry  units with shapes as shown in Figures B.23 
to B.28, where the voids run continuously over the vertical joi nt, the length of the unit has no influence on the 
thermal transmittance.  NOTE 2  The heat flow direction is indicated in the drawings in  Annex B by means of an arrow. 
 
8. Determination of the ther mal transmittance of masonry 
 
Calculation of the thermal transmittance U shall be made according to EN ISO 6946. 
 
9. Specific heat capacity 
 
The  thermal   mass  of  the  construction  has  a  significant   influence  on  the  heating   and    cooling 
requirements of buildings. Valu es for the specific heat capacit y Cp are therefore given in Annex A. 
 
10. Rounding rules for גvalues for masonry 
 
The value should be rounded according to EN ISO 10456.   
 
  
 
 
 
  
 
20  © KEBS 2019 — All rights reserved Annex  A  
(normative) 
 
 
Tabulated  ג10,dry,mat ꞏValueosf materials  used  for  masonry products 
 
 
The water vapour diffusion coefficient µ is defined as the fact or, which describes how many times higher the 
diffusion resistance of a material layer is, than the resistanc e of an air layer with the same thickness under the 
same conditions. To compare the diffusion resistance of two bui lding elements, it is necessary to multiply the 
µ-factor by the thickness of the respective layer, which leads to a figure with the dimension m.  The diffusion 
behaviour is different, whether it is diffusion into a building  component (lower values) or out of the building 
component (drying period, higher value). 
 
 
 
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exists  (e.g. 
for new products).  Therefore, no 50% and 90% fractiles ( Pvalues are to be 
understood as safe values for all different types of aggregates . 
 
 
 
 
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(informative) 
 
 
Rdry,mas – or גdry,mas -Values of masonry built from a range of masonry units containi ng 
formed voids 
 
 
NOTE: The range of size and types of unit and void pattern is i ntended to be representative of units typically 
found on the market. It is not intended to be an exhaustive lis t covering all combinations of material, unit size, 
void configuration and size. The procedure according to 7.3.3 w ill need to be followed for configurations of 
units not covered by these tables. 
 The geometries are defined n umerically by two figures: 
 
- the number of rows of voids; and 
-  the number of voids in  a row. 
For example 3,7/1,6 means that th is type of unit has 3,7 rows o f voids per 100 mm thickness and 1,6 voids in  
a  row per 100 mm length, which  means 11   rows of voids in th e case of a masonry thickness of 300 mm and 
4 voids in a row in the case of a unit length of 250 mm. The tr ansverse web portion is defined as the sum of 
the thicknesses of the transverse webs divided by the unit leng th expressed as a percentage and is given for 
each geometry as additional information. 
 Further information is given for each geometry about the dimens ions, which were the basis for the numerical 
calculation. 
 
The following tabulated values should be used as a  basis for t he determination of unit equivalent
 ג10,dry,unit -
values    or Rdry,mas – or ג10,dry,mas -values  of the masonry if neither an individual test measureme nt nor a 
calculation are available for a specific product. 
 
The values in this annex were calculated using a three-dimensio nal Finite-Difference-Program. 
 The equivalent thermal   conductivity of the   air in the   voi ds was determined   according to EN ISO 6946:2007, 
B.2.   The program used was checked through the examples shown in Annex D and fulfils all the requirements 
for appropriate calculation procedures.  
The theoretical background for the selection of geometries was knowledge about the principal geometrical 
influences on the thermal resistance:  
- number of rows of voids; 
- thickness of the material webs between the voids (transverse web portion); 
- voids staggered or "in line"; 
- shape of the voids. 
 
(experience shows that the last t wo factors can be neglected-fo r the purpose of tabulated values). 
 
The tabulated values in the following tables are generally give n for masonry with only horizontal mortar joints. 
 
In some cases, the tabulated values are split into two, one of which is valid without vertical mortar joints and 
the second is valid with vertical mortar joints.  For those geo metry classes, where no separate values are given 
use the calculation procedure in 7.3.3.    
30  © KEBS 2019 — All rights reserved  
The thermal  resistance    of the  mortar  joints  on which  th e  calculation    results    are  based  can be  derived 
in  different  ways.   Full bed mo rtar  joints  may be provided    using  an insulating   mor tar  or it is  possible  to 
reach  the  same   resistance/equivalent     conductivity   by  making  twin strip  mortar  joints  from  a  general 
purpose  mortar,   possible  with   a strip of insulating  mate rial   in between. 
 The values are grouped according to the material of the masonry  units, nevertheless, the calculation results  
are also valid for other materials, if the geometry and the the rmal conductivity of the material is the same. 
 
The resistance-values are tabulated as resistance per 100 mm, w hich means for example that for a masonry 
of 300 mm thickness the values have to be multiplied by 3. As a dditional information, the calculation results 
are also given as
 ג10,dry,mas -values of the masonry, which are calculated according to the f ollowing equation: 
 
 
The values for the percentage of voids given in the tables are related to the cross section of the units. 
 
 
 
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Basic dimensions:  I = 300 mm, w = 250 mm, hunit = 238 mm, hmor = 12 mm                                                                 A 
 
NOTE: There are no values given for a combination of such a mas onry unit with a mortar with a conductivity 
of 0,16 W/mꞏK,  because such a combination would not be sensibl e. 
 
 
 
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56  © KEBS 2019 — All rights reserved Annex C  
(informative) 
 
 
Example of how to use the tables in Annex B 
 
 
 
 
A vertical perforated clay unit with the dimensions I x w x h unit = 250 mm x 380 mm x 238 mm has a dry mass 
of approximately 13,6 kg.   The  horizontal joint  is  made wit h  a  thermal  insulating  mortar with a  thermal 
ג10,dry,mat of  0,16 W/m·K   The net dry density of the brick is approximat ely 1500 kg/m3,   which 
can be derived from the mass and the net volume of the unit (th e net volume needs to be determined according 
to DKS 2802-2). 
 
Figure C.1   -   Example of a vertically perforated clay unit 
 
The unit has 19 rows of holes, which means 5 rows of holes per 100 mm thickness, and either 3 or 4 holes per 
row, which  means 1,2 or  1,6 holes per  100 mm length. There i s   no geometry class 5/1,2, therefore the 
relevant table is Table B.3  - Geometry 5/1,6.   The values fro m this table are on the safe side, because of the 
ג10,dry,mat -value        
for a  clay  unit  material with  a  density  of  1500 kg/m3    can  be taken  as  0,43 W/mꞏK  (if  an  individual test 
is available the  measured value  can  be taken).  From the fi rst column in Table B.3 
ג10,dry,morג10,dry,mas  of 0,17 
W/mꞏK is obtained. As the unit has a thickness of 38 cm, the R-value for the dry masonry is 0,58 x 3,8 = 2,204 
DKS 2803:2019  
© KEBS 2019 — All rights reserved   57 m2ꞏK/W. The unit has a tongue and groove system in the vertical j oint, therefore no mortar correction is 
necessary (even if there was a vertical mortar joint, it could be neglected, because a thermal insulating mortar 
is used). No correction is necessary for deviating dimensions, because the length and height of the unit are 
identical with the "basic dimensions" of geometry in Table B.3) . 
 
To  produce a design thermal  value, the  dry  resistance  has to  be corrected  according to  moisture. The 
moisture correction coefficient  is taken  as 6%  per volume  p ercent change of moisture as  no individual 
measurement is available. Therefore, for a practical moisture c ontent of 1 % by volume the dry resistance has 
to be multiplied  by 0,94, which  leads to a design resistance of 2,204 x 0,94 =  2,072 m2ꞏK/W;  a practical 
moisture content of 1,5 % by volume leads to a design resistanc e of 2,204 x 0,91 = 2,006 m2ꞏK/W.  The design 
U-value would then be in the first case 0,45 W/(m2ꞏK) in the second case 0,46 W/(m2ꞏK).  
 
 
  
 
  
 
  
 
  
 
  
 
   
 
  
 
   
 
  
 
  
 
  
 
   
 
  
 
  
 
   
58  © KEBS 2019 — All rights reserved Annex D 
(normative) 
 
 
Requirements for appropriate calculation procedures 
 D.1 Capabilities of the program 
 The user shall be supplied with the necessary information about  the capability of the program to simulate the 
relevant characteristic properties of the physical component un der considerations. Therefore,  the following 
aspects of the heat flow model shall be defined:  
- 2 or 3 dimensional; 
- rectangular or non-rectangular shape; 
- isotropic or non-isotropic conductivity. In this  case: 
- general anisotropy; 
- partial anisotropy (with respect to the eigenvalues or eigenv ectors of conductance); 
- voids; 
- equivalent conductivity or resistance (convective and radiati ve part);  
- radiation exchange and equivalent conductivity (convective pa rt);  
- radiation exchange and internal air flow model; 
- the thermal resistance of the voids has to be calculated acco rding to EN ISO 6946; 
- mass transfer (air-, moisture- transport from environment to e nvironment); 
- surface resistances to be taken from EN ISO 6946. 
There is no specific preference related to the numerical method s incorporated; on the other hand, the user 
shall be informed about the advantages and restrictions of each  method. 
 
D.2 Input data and results 
 
Input data shall be presented, to make it possible for a third party to do the same calculation. The following 
calculation results sha ll at least be provided: 
 
- minimum surface temperature of the test component on all side s; 
- maximum surface temperature o f the test component on all side s; 
- 2D or 3D thermal coupling coefficient (W/(mꞏK)  or W/K respec tively); 
- number and type of elements.  DKS 2803:2019  
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The program shall be tested by calculating   reference cases ac cording to EN 10211. 
 D.4 Reference cases 
 
D.4.1     Case 1:ג10,dry,unit  of  a  masonry   
unit (vertically  perforated   unit). 
 
 
 
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© KEBS 2019 — All rights reserved   61 D.4.2     Case 2:   Calculation    of thermal    resistance Rdry,mas    of  masonry   consisting    of  vertically    
perforated masonry  units and internal/  external  plaster  lay ers. 
 
 
 
 
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D.4.3    CASE 3:   Calculation of thermal resistance Rt of masonry consisting of masonry units, horizontal 
mortar layers, vertical mortar pockets and additional external insulation layer.  
 
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(informative) 
 
 
Evaluation of conformity 
 
ג10,dry,unit  or equivalent 
ג10,dry,unit - values will be part of the evaluation of conformity system is g iven in the following table: 
 
 
 
ג10,dry,mat -value for a  batch of masonry unit may be determined based on direct 
testing of thermal conductivity . If so the following procedure should be used: 
 
ג10,dry,unit - A-
10,dry,unrvalue  may be based  on the  value  obtained from  th e  alternative test  method after  applying the 
established correlation correction.  
NOTE: Care should be taken that the test specimens are represen tative of the masonry product itself. An 
appropriate way to ensure this is to cut specimens from masonry  units.  
  
 
  
 
  
 
  
 
  
 
  
 
   
 
  
 
   
 
  
 
  
 
  
 
   
 
  
 
  
 
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(informative) 
 
 
Alternative procedure for the mo isture correction of units with  formed voids 
 
 
 The principle of this method is to correct the design moisture content according to the percentage of voids. It 
is a safe approximation and may be used as an alternative to pr ocedure 2 in Clause 6. 
 
From the moisture correction coefficient and the design moistur e content, the following formulae can be used: