EN ISO 6946:1996

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.RSORWQDBauteile - Wärmedurchlaßwiderstand und Wärmedurchgangkoeffizient - Berechnungsverfahren (ISO 6946:1996)Composants et parois de bâtiments - Résistance thermique et coefficient de transmission thermique - Méthode de calcul (ISO 6946:1996)Building components and building elements - Thermal resistance and thermal transmittance - Calculation method (ISO 6946:1996)91.120.10Toplotna izolacija stavbThermal insulation91.060.01Stavbni elementi na splošnoElements of buildings in generalICS:Ta slovenski standard je istoveten z:EN ISO 6946:1996SIST EN ISO 6946:1997en01-december-1997SIST EN ISO 6946:1997SLOVENSKI
STANDARD



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



SIST EN ISO 6946:1997



INTERNATIONAL STANDARD First edition 1996-08-15 Building components and building elements - Thermal resistance and thermal transmittance - Calculation method Composants et parois de batiments - Rkstance thermique et coefficient de transmission thermique - M&hode de calcul Reference number IS0 6946:1996(E) SIST EN ISO 6946:1997



IS0 6946:1996(E) Contents Page 1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 Normative references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 3 Definitions and symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 4 Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 5 Thermal resistances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 6 Total thermal resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7 Thermal transmittance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Annexes A Surface resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 B Thermal resistance of unventilated airspaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 C Calculation of the thermal transmittance of components with tapered layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 D Corrections to thermal transmittance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 E Examples of corrections for air gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 0 IS0 1996 All rights reserved. Unless otherwise specified, no part of this publication may be repro- duced or utilized in any form or by any means, electronic or mechanical, including photo- copying and microfilm, without permission in writing from the publisher. International Organization for Standardization Case Postale 56 l CH-1211 Geneve 20 l Switzerland Printed in Switzerland II SIST EN ISO 6946:1997



@ IS0 IS0 6946: 1996(E) Foreword IS0 (the International Organization for Standardization) is a worldwide fed- eration of national standards bodies (IS0 member bodies). The work of preparing International Standards is normally carried out through IS0 technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be rep- resented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. IS0 col- laborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are cir- culated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. International Standard IS0 6946 was prepared by the European Commit- tee for Standardization (CEN) in collaboration with ISOK 163, Thermal in- sulation, Subcommittee SC 2, Cakulation methods, in accordance with the Agreement on technical cooperation between IS0 and CEN (Vienna Agreement). This first edition cancels and replaces IS0 6946-l :I 986. IS0 6946-2:1986 was withdrawn in 1995. Annexes A, B, C and D form an integral part of this International Standard. Annex E is for information only. SIST EN ISO 6946:1997



IS0 6946: 1996(E) 0 IS0 Introduction The thermal transmittance calculated according to this standard is suitable for determining heat flow through building components that are within the scope of this standard. For most purposes heat flows can be calculated with the following tem- peratures: - internal: dry resultant temperature; external: air temperature. SIST EN ISO 6946:1997



@ IS0 Scope IS0 6946: 1996(E) This standard gives the method of calculation of the thermal resistance and thermal transmittance of building components and building elements, excluding doors, windows and other glazed units, components which involve heat transfer to the ground, and components through which air is designed to permeate. The calculation method is based on the appropriate design thermal conductivities or design thermal resistances of the materials and products involved. The method applies to components and elements consisting of thermally homogeneous layers (which can include air layers). The standard also gives an approximate method that can be used for inhomogeneous layers, except cases where an insulating layer is bridged by metal. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and IS0 maintain registers of currently valid International Standards. IS0 10456:- I), Thermal insulation - Building materials and products - Determination of declared and design thermal values. IS0 73451987, Thermal insulation. 3 Definitions and symbo I 31 . Definitions - Physical quantities and definitions. For the purposes of this standard, the following definitions and those given in IS0 7345 apply. 3.1.1 building element: Major part of a building such as a wall, floor or roof. 1) To be published. SIST EN ISO 6946:1997



IS0 6946: 1996(E) 3.1.2 building component: Building element or a part of it. NOTE - In this standard the word “component” is used to indicate both element and component. 3.1.3 design thermal value: Design thermal conductivity or design thermal resistance. NOTE - A given product can have more than one design value, for different applications or environmental conditions. 3.1.4 design thermal conductivity: Value of thermal conductivity of a building material or product under specific external and internal conditions which can be considered as typical of the performance of that material or product when incorporated in a building component. 3.1.5 design thermal resistance: Value of thermal resistance of a building product under specific external and internal conditions which can be considered as typical of the performance of that product when incorporated in a building component. 3.1.6 thermally homogeneous layer: Layer of constant thickness having thermal properties which are uniform or which may be regarded as being uniform. 32 . Symbols and units Symbol Quantity A area R design thermal resistance Rs thermal resistance of airspace R se external surface resistance R si internal surface resistance RT total thermal resistance (environment to environment) Ri upper limit of total thermal resistance RY lower limit of total thermal resistance R U thermal resistance of unheated space u thermal transmittance d thickness h heat transfer coefficient a design thermal conductivity Unit m* m*KM/ m*KM/ m*KM/ m*KM/ m*K/W m*KM/ m*KM/ m*KM/ W/( m**K) m W/(m**K) W/( m-K) SIST EN ISO 6946:1997



@ IS0 IS0 6946:1996(E) 4 Principles The principle of the calculation method is to: a) obtain the thermal resistance of each thermally homogeneous part of the component; W combine these individual resistances so as to obtain the total thermal including (where appropriate) the effect of surface resistances. resistance of the component, Thermal resistances of individual parts are obtained according to 5.1. The values of surface resistance given in 5.2 are appropriate in most cases. Annex A gives detailed procedures for low-emissivity surfaces, specific external wind speeds, and non-planar surfaces. Air layers may be regarded as thermally homogeneous for the purposes of this standard. Values of the thermal resistance of large air layers with high-emissivity surfaces are given in 5.3, and annex B gives procedures for other cases. The resistances of the layers are combined as follows: a) for components consisting of thermally homogeneous layers, obtain the total according to 6.1 and the thermal transmittance according to clause 7; thermal resistance b) for components having one or more thermally inhomogeneous layers, obtain the total thermal resistance according to 6.2 and the thermal transmittance according to clause 7; c) for components containing a tapered layer, thermal resistance according to annex C. obtain the thermal transmittance and/or the total Finally, corrections are applied to the thermal transmittance if appropriate according to annex D, to allow for the effects of air gaps in insulation, mechanical fasteners penetrating an insulation layer, and precipitation on inverted roofs. The thermal transmittance so calculated applies between the environments on either side of the component concerned, for example internal and external environments, two internal environments in the case of an internal partition, internal environment and an unheated space. Simplified procedures are given in 5.4 for treating an unheated space as a thermal resistance. SIST EN ISO 6946:1997



IS0 6946:1996(E) 5 Thermal resistances 51 . Thermal resistance of homogeneous layers Design thermal values can be given as either design thermal conductivity or design thermal resistance. If thermal conductivity is given, obtain the thermal resistance of the layer from: R d =- h where d a is the thickness of the material layer in the component; is the design thermal conductivity of the material, either calculated according to ISO/DIS 10456.2 or obtained from tabulated values. NOTE - The thickness d may be different from the nominal thickness (e.g. when a compressible product is installed in a compressed state, d is less than the nominal thickness). If relevant, d should also make appropriate allowance for thickness tolerances (e.g. when they are negative). Thermal resistance values used in intermediate calculations shall be calculated to at least 3 decimal places. 5.2 Surface resistances Use the values in table 1 for plane surfaces in the absence of specific information on the boundary conditions. The values under “horizontal” apply to heat flow directions 230” from the horizontal plane. For non-planar surfaces or for specific boundary conditions use the procedures in annex A. Table 1 - Surface resistances (in m2XAA/) Direction of heat flow R si R se Upwards 0,lO 0,04 Horizontal 0,13 0,04 I Downwards 0,17 0,04 NOTE - The values in table 1 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, it is recommended that the values for horizontal heat flow are used. 4 SIST EN ISO 6946:1997



@ IS0 IS0 6946: 1996(E) 5.3 Thermal resistance of air layers The values given in this subclause apply to an air layer which: - is bounded by two faces which are effectively parallel and perpendicular to the direction of heat flow and which have emissivities not less than 0,8; - has a thickness (in the direction of heat flow) of less than 0,l times each one of the other two dimensions, and not greater than 0,3 m; NOTE - A single thermal transmittance should not be calculated for components containing air layers thicker than 0,3 m. Rather, heat flows should be calculated by performing a heat balance (see ISO/DIS 13789, Thermal performance of buildings - Transmission heat loss coefficient - Calculation method). - has no air interchange with the internal environment. If the above conditions do not apply, use the procedures in annex B. 5.3.1 Unventilated air layer An unventilated air layer is one in which there is no express provision for air flow through it. Design values of thermal resistance are given in table 2. The values under “horizontal” apply to heat flow directions *30° from the horizontal plane. Table 2 - Thermal resistance (in m2WVV) of unventilated air layers: high emissivity surfaces Thickness Direction of heat flow of air layer mm Upwards Horizontal Downwards 0 0,oo 0,oo 0,oo 5 0,ll 0,ll 0,ll 7 0,13 0,13 0,13 10 0,15 0,15 0,15 15 0,16 0,17 0,17 25 0,16 0,18 0,19 50 0,16 0,18 0,21 100 0,16 0,18 0,22 300 0,16 0,18 0,23 NOTE - Intermediate values may be obtained by linear interpolation. SIST EN ISO 6946:1997



IS0 6946: 1996(E) 0 IS0 An air layer having no insulation layer between it and the external environment but with small openings to the external environment shall also be considered as an unventilated air layer, if these openings are not arranged so as to permit air flow through the layer and they do not exceed: - 500 mm* per m length for vertical air layers - 500 mm* per m* of surface area for horizontal air layers.‘) NOTE - Drain openings (weep holes) in the form of open vertical joints in the outer leaf of a masonry cavity wall are not regarded as ventilation openings. 5.3.2 Slightly ventilated air layer A slightly ventilated air layer is one in which there is provision for limited air flow through it from the external environment by openings within the following ranges: - > 500 mm* but 2 1500 mm* per m length for vertical air layers - > 500 mm* but 2 1500 mm* per m* of surface area for horizontal air layers? The design thermal resistance of a slightly ventilated air layer is one half of the corresponding value in table 2. If, however, the thermal resistance between the air layer and the external environment exceeds 0,15 m*XM/, it shall be replaced by the value 0,15 m*WVV. 5.3.3 Well ventilated air layer A well ventilated air layer is one for which the openings between the air layer and the external environment exceed: - 1500 mm* per m length for vertical air layers - 1500 mm* per m* of surface area for horizontal air layers?) The total thermal resistance of a building component containing a well-ventilated air layer shall be obtained by disregarding the thermal resistance of the air layer and all other layers between the air layer and external environment, and including an external surface resistance corresponding to still air (i.e. equal to the internal surface resistance of the same component). ‘) For vetti cal air layers the range is expressed the area of openi ngs per square metre area. as the area of openings per metre length. For horizontal air layers it is expressed as SIST EN ISO 6946:1997



@ IS0 IS0 6946: 1996(E) 5.4 Thermal resistance of unheated spaces When the external envelope of the unheated space is not insulated the following simplified procedures, treating the unheated space as a thermal resistance, may be applied. NOTE - ISO/DIS 13789, Thermal performance of buildings - Transmission heat loss coefficient - Calculation method, gives general, and more precise, procedures for the calculation of heat transfer from a building to the external environment via unheated spaces, and should be used when a more accurate result is required. For crawl spaces below suspended floors see ISO/DIS 13370, Thermal performance of buildings - Heat transfer via the ground - Calculation method. 5.4.1 Roof spaces For a roof structure consisting of a flat, insulated ceiling and a pitched roof, the roof space may be regarded as if it were a thermally homogeneous layer with thermal resistance as given in table 3. Table 3 - Thermal resistance of roof spaces Characteristics of roof R U m*XM/ 1 Tiled roof with no felt, boards or similar 0,06 2 Sheeted roof, or tiled roof with felt or boards or similar under the tiles 02 9 3 As 2 but with aluminium cladding or other low emissivity surface at underside of roof 03 9 4 Roof lined with boards and felt 03 9 NOTE - The values in table 3 include the thermal resistance of the ventilated space and the thermal resistance of the (pitched) roof construction. They do not include the external surface resistance (R,,). SIST EN ISO 6946:1997



IS0 6946:1996(E) 0 IS0 5.4.2 Other spaces When the building has a small unheated space attached to it, the thermal transmittance between the internal and external environments can be obtained by treating the unheated space together with its external construction components as if it were an additional homogeneous layer with thermal resistance Ru given by: A R” = 0,09 + 0,4’ A U subject to R, < 0,5 m*X/W, where A i is the total area of all components between the internal environment and the unheated space; A e is the total area of all components between the unheated space and the external environment. NOTES 1 Examples of small unheated spaces include garages, store rooms and conservatories. (2) 2 If there is more than one component between the internal environment and the unheated space, R, should be included in the calculation of the thermal transmittance of each such component. 8 SIST EN ISO 6946:1997



@ IS0 IS0 6946: 1996(E) 6 Total thermal resistance If the total thermal resistance is presented as a fina ,I result, it shall be rounded to two decima I places. (3) 61 . Total thermal resistance of a building component consisting of homogeneous layers The total thermal resistance RT of a plane building component consisting of thermally homogeneous layers perpendicular to the heat flow shall be calc
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