2 IFBS 4.03 Contents Page Contents Page

1  Introduction ........................................ 4 1.1  Thermal-bridge investigations – a

facet of sustainable building ................ 4 

1.2  Lightweight metal construction using sandwich panels ........................ 4 

2  Fundamentals .................................... 4 2.1  Energy Saving Ordinance .................... 4 

2.2  Thermal-bridges .................................. 5 

2.3  Specific requirements for minimum thermal protection in winter ................. 5 

2.4  Numerical calculation of heat transfer ................................................ 6 

2.4.1  Fundamentals of method of calculation ............................................ 6 

2.4.2  Boundary conditions for calculation of heat transfer .................. 7 

2.4.3  Material properties ............................... 7 

2.5  Heat transfer coefficient as a significant factor for energy efficiency .............................................. 7 

3  Thermal insulation of metal sandwich constructions ................... 9 

3.1  General ................................................ 9 

3.2  Determination of the thermal transmittance of an element .............. 11 

3.2.1  Procedure .......................................... 11 3.2.2  Effect of profile shape ........................ 12 3.2.3  Effect of longitudinal joints ................. 13 3.2.3.1  General .............................................. 13 3.2.3.2  Types of longitudinal joint .................. 13 3.2.4  Effect of fasteners .............................. 14 3.2.5  Design value of thermal

transmittance ..................................... 14 

3.3  Thermal-bridge effect of junctions ..... 14 3.3.1  General .............................................. 14 3.3.2  Determination of linear thermal

transmittance Ψ ................................. 15 3.3.3  Comments on the junction design

details in the Annexes ....................... 16 3.3.4  Evaluation of thermal-bridge effect

of junction design detail ..................... 17 

3.4  Proof of minimum thermal protection in winter in accordance with DIN 4108-2 ................................. 17 

3.4.1  Elements ............................................ 17 3.4.2  Junctions ........................................... 17 3.4.3  Anomalous boundary conditions ....... 17 

4  Results of numerical calculations ...................................... 18 

4.1  Steel polyurethane sandwich constructions ...................................... 18 

4.1.1  Minimum thermal protection in winter according to DIN 4108-2 .......... 18 

4.1.1.1  Elements ............................................ 18 4.1.1.2  Junctions ............................................ 18 4.1.2  Transmission heat transfer within

element .............................................. 18 4.1.2.1  General .............................................. 18 4.1.2.2  Example of results for trapezium-

shaped profile ..................................... 18 4.1.2.3  Example of results for wave-

shaped profile ..................................... 19 4.1.2.4  Example of results for longitudinal

joint ..................................................... 19 4.1.2.5  Example of results of correction

values for fasteners ............................ 19 4.1.3  Transmission heat transfer of

junctions ............................................. 20 

4.2  Steel mineral wool sandwich constructions ...................................... 21 

4.2.1  Elements ............................................ 21 4.2.2  Junctions ............................................ 21 

4.3  Aluminium polyurethane sandwich constructions ...................................... 21 

4.3.1  Elements ............................................ 21 4.3.2  Junctions ............................................ 21 

5  Example of use of a demonstration building ................... 21 

5.1  Concept of demonstration building ..... 21 5.1.1  Idea and dimensioning ....................... 21 5.1.2  Linear thermal transmittance of

junctions ............................................. 24 5.1.3  Steady-state ground heat transfer

coefficient ........................................... 24 

5.2  Effect of thermal-bridges on heat transfer ............................................... 27 

5.2.1  Results for standard design details .... 27 5.2.2  Results for improved design

details ................................................. 27 

5.3  Energy efficiency of demonstration building ............................................... 29 

5.3.1  Transmission heat transfer coefficient ........................................... 29 

5.3.2  Specific transmission heat transfer coefficient ........................................... 29 

5.3.3  Annual heat use ................................. 29 

6  Summary ........................................... 33 

IFBS 4.03 3

Contents Page Contents Page

7  Bibliography ..................................... 35 

8  Figures .............................................. 36 

9  Tables ................................................ 37 

10  Abbreviations ................................... 38 

Annex A Steel polyurethane sandwich constructions, junction details 39

Roof junctions: End laps 40

Gable ends 44

Eaves 64

Ridges 72

Mono ridges 74

Skylight junctions 82

Continuous roof-light junctions 88

Flat-roof junctions 98

Wall junctions: Floor slab junctions 108

External corners 144

Large-door junctions 150

Door junctions 158

End laps 166

Pilaster strips 170

Window junctions 172

Annex B Steel mineral wool sandwich constructions, junction details 185 Gable ends 186

Eaves 190

External corners 194

Annex C Aluminium polyurethane sandwich constructions, junction details 199 External corners 200

4 IFBS 4.03

1 Introduction

1.1 Thermal-bridge investigations – a facet of sustainable building

Sustainable building is the most important topic in the building and construction industry. It serves to maintain value in combination with protecting the environment and taking social needs and economics into account. Energy consumption plays a dominant role here be-cause it has a very marked effect on the evalua-tion of a building with respect to sustainability. In order to be able to construct sustainable buildings, one has to investigate all aspects affecting the energy requirement of a building and evaluate them with respect to potential en-ergy savings.

The energy-related performance of building envelopes is determined by their heat transmis-sion and heat convection properties. Heat transmission takes place as one-dimensional heat flow in the thermally undisturbed control zone of elements of the building envelope; in addition, there are two- and three-dimensional heat flows within linear and point thermal-bridges.

As a central design code for sustainable build-ing, the Energy Saving Ordinance [12] requires that the effect ofdesign-related thermal-bridges on the annual heat use is kept as low as possi-ble in accordance with good engineering prac-tice and measures that are economically ac-ceptable for the specific case.

1.2 Lightweight metal construction using sandwich panels

Lightweight metal construction is used primarily in industrial and commercial building. One dis-tinguishes between double-skin designs and sandwich constructions (see [13]). Sandwich constructions are made from individual, indus-trially manufactured sandwich panels. These are ready-to-install roof and wall elements con-sisting two thin metal covering layers. Sandwich panels are available with linear-, trapezium- or wave-shaped profiles and joined in a shear-resistant manner via a core insulation.

A very high standard of thermal insulation can be achieved using metal sandwich panels. However, the joining of the prefabricated ele-ments produces joints and junctions that also have to satisfy the demands made on the en-ergy-saving thermal insulation.

2 Fundamentals

2.1 Energy Saving Ordinance The energy requirement depends on various design and operating factors such as the stan-dard of thermal insulation, type of ventilation, losses during heat generation, lighting concep-tand cooling system. The Energy Saving Ordi-nance is one element of the German Federal Government’s climate protection policy to re-duce the energy requirement of buildings and thus carbon dioxide emissions. The Energy Saving Ordinance 2009 (EnEV 2009) [12] has been in force since October, 1st 2009.

EnEV 2009 attempts to take into account all the variables that affect the energy requirement of a building during the operating phase, as can be seen from the complexity of the method of cal-culation.

A calculation of the annual primary energy re-quirement is necessary for all non-residential buildings as soon as at least one of the follow-ing forms of conditioning is used: heating, cool-ing, ventilation, humidifying, lighting and provi-sion of hot, drinking-quality water. The boundary conditions (e.g. inside temperature, internal sources of heat, air-change rates) should be adjusted in accordance with the utilisation pro-file chosen for the calculations.

§4 of EnEV 2009 requires that the following approach be adopted in order to determine the maximum permissible values: non-residential buildings have to be constructed in such a way that the annual primary energy requirement for space heating, water heating, ventilation, cool-ing and installed lighting does not exceed the annual primary energy requirement of a refer-ence building of the same geometry, net floor space, alignment and use, including the ar-rangement of the units with the technical design shown in Annex 2 Table 1 of the ordinance.

For the building that is to be erected, the so-called “reference building method” requires a second calculation to be made for which refer-ence methods of execution or the specified val-ues given in Annex 2 Table 1 of EnEV 2009 are stipulated for all elements of the building enve-lope (e.g. transmission heat transfer, glazing, solar shading) as well as the plant engineering (e.g. heating, air-conditioning, lighting). The process used to calculate the primary energy requirement for non-residential buildings must conform to DIN V 18599 [3].

10 IFBS 4.03

Fig. 2 shows an example of the approach adopted to determine design values for the thermal protection of metal sandwich construc-tions for buildings with normal indoor tempera-ture.

The material propertiesand boundary condi-tionsgiven in Section 2.4.2 are used in the nu-merical calculations of the heat transfer. The thickness of the interior and exterior coating layers of metal sandwich elements is usually between 0,4 mm and 0,75 mm (see [19] and

[20]). To determine the thermal-bridge effects, the thickness of the inner and outer covering layers is taken to be uniform with t = 0,75 mm for the numerical calculations.

Furthermore, it is assumed that the joints of junctions and all other thermal weak spots (e.g. point thermal-bridges) are permanently imper-meable to air and thus the heat transmission in the zone of thermal influence of thermal-bridges only takes place by heat conduction.

Fig. 2: Method of determining the transmission heat transfer and providing proof of the minimum

thermal protection

Metal Sandwich Construction(regular tempered buildings)

Regular element• Roof• External wall

Junctions• linear (Annex A)

FEM-CalculationMinimum thermal

protection

Design value of the thermal

transmittance Ud,SE

Determination of the influence of thermal bridges

• profile shape (Δe)• longitudinal joints

(ΔUj)• fasteners (ΔUf)

FEM-Calculation Heat transfer

Verification ofDIN 4108-2• f0,25 ≥ 0,7 [ - ]• R ≥ 1,75 (m²·K)/W

FEM-CalculationMinimum thermal

protection

Verification ofDIN 4108-2• f0,25 ≥ 0,7 [ - ]

FEM-Calculation Heat transfer

Design value of the linear thermal

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IFBS 4.03 23

Fig. 16: Longitudinal and transverse cross section of demonstration hall

Changes to demonstration hall Linear thermal-bridge Ψ [W/(m·K)]

Detail Junction L [m] Standard Improved

A Ridge 2 · 5,0 -0,002 -0,002

B Continuous roof

light

2 · (l-10,0) + 4,0 0,794 0,320

C Roof end lap 2 · l 0,005 0,004

D Gable end 2 · b 0,160 0,012

E Eaves 2 · l 0,574 0,029

F External corner 4 · h 0,060 -0,036

G Façade end lap 2 · (b+l) 0,981 0,016

H Large door, top 2 · 4,0 0,524 0,155

Parameters:

Width 10 m ≤ B ≤ 50 m

Length 20 m ≤ L ≤ 100 m

Height 5 m ≤ H ≤ 25 m

I Large door, side 4 · 4,0 0,662 0,206

J Door, top 2 · 1,0 1,263 0,301

K Door, side 4 · 2,0 0,881 0,262

L Window, top 2 · (l-10,0) 0,447 0,041

M Window, side 4 · 1,0 0,342 0,054

N Window, bottom 2 · (l-10,0) 0,079 0,054

O Floor slab 2 · (b+l) 1,126 -0,676

Table 12: Changes to demonstration hall – effect of thermal-bridges

36 IFBS 4.03

8 Figures Fig. 1:  Proof of minimum thermal

protection in winter in accordance with DIN 4108-2 .................................. 7 

Fig. 2:  Method of determining the transmission heat transfer and providing proof of the minimum thermal protection ............................. 10 

Fig. 3:  Notation used to describe cross sections; upper profile is trapezium-shaped, lower profile is wave-shaped .................................... 12 

Fig. 4:  Profile shapes for the covering layers of metal sandwich elements ... 13 

Fig. 5:  Different types of longitudinal joint .... 14 Fig. 6:  Calculation of linear thermal

transmittance Ψ ................................ 16 Fig. 7:  FE model for external corner of a

sandwich element ............................. 16 Fig. 8:  Temperature distribution ................... 16 Fig. 9:  FE model for a longitudinal joint

(Type 1) ............................................ 19 Fig. 10:  Temperature distribution (Type 1) .... 19 Fig. 11:  Heat flux distribution (Type 1) ........... 19 Fig. 12:  Ψj-values for different products ......... 19 Fig. 13:  FE model of SE fixture ...................... 20 Fig. 14:  Heat flux distribution ......................... 20 Fig. 15:  Effect of stainless steel screws ......... 20 Fig. 16:  Longitudinal and transverse cross

section of demonstration hall ............ 23 Fig. 17:  Floor slab without thermal

insulation (“unins”) ............................ 24 Fig. 18:  Floor slab with thermal insulation

(“ins”) ................................................ 24 Fig. 19:  Specific steady-state ground heat

transfer coefficient Hg’ for floor slab without thermal insulation (as an example of junction design details A.34 and A.44) .................................. 26 

Fig. 20:  Specific steady-state ground heat transfer coefficient Hg’ for floor slab with thermal insulation (as an example of junction design details A.36 and A.46) .................................. 26 

Fig. 21:  Effect of changes to demonstration hall on thermal-bridge allowance for standard details ........................... 28 

Fig. 22:  Transmission heat transfer coefficient within the element and the junction ....................................... 28 

Fig. 23:  Effect of changes to demonstration hall on thermal-bridge allowance for improved details .......................... 28 

Fig. 24:  Transmission heat transfer coefficient for the demonstration hall broken down into elements and junctions .................................... 31 

Fig. 25:  Transmission heat transfer coefficient for the demonstration hall comparing standard thermal-bridge coefficients and exact calculations ........................................ 31 

Fig. 26:  Specific transmission heat transfer coefficient for the demonstration hall – requirements, reference values and calculations ..................... 32 

Fig. 27:  Annual heat use of the demonstration hall showing the effect of standard details and improved details, with and without air tightness testing (ATT) in each case ................................................... 32 

IFBS 4.03 37

9 Tables Table 1:  Maximum values for thermal

transmittances according to EnEV 2009 (non-residential buildings) .......................................... 5 

Table 2:  Boundary conditions for proof of conformity with minimum thermal protection .......................................... 6 

Table 3:  Boundary conditions for temperature ...................................... 7 

Table 4:  Boundary conditions for heat-transfer resistance ............................ 7 

Table 5:  Thermal conductivity of the materials ........................................... 8 

Table 6:  Classification of linear thermal-bridges ............................................ 17 

Table 7:  Results for trapezium-shaped profile .............................................. 18 

Table 8:  Results for wave-shaped profile ..... 18 Table 9:  Result of FEM calculations of

thermal transmittance (χb-values) .. 20 Table 10: Dimensions of the heat-

transmitting envelopes [m] .............. 22 Table 11: Thermal transmittances of the

demonstration hall .......................... 22 Table 12: Changes to demonstration hall –

effect of thermal-bridges ................. 23 

IFBS 4.03 39

Annex A

Steel polyurethane sandwich constructions Roof junctions

40 IFBS 4.03

A.1 End lap, 1.1.1 (IFBS 4.02 [21], Drawing 1.1.1)

Steel sandwich panel

Tel.: +49 211 91427-0 Internet: www.ifbs.de Detail: End lap

IFBS 4.03 41

Thickness SE Ψ [W/(m·K)] f0,25 [-] L with f0,25 < 0,7 [mm]

60 mm 0,003 0,90 0

80 mm 0,005 0,93 0

200 mm 0,009 0,97 0

IFBS 4.03 185

Annex B

Steel mineral wool sandwich constructions Junction details

186 IFBS 4.03 B.1 Verge (Detail 1.5.1c) (IFBS 4.02 [21], Drawing 1.5.1c)

Steel mineral wool sandwich panel

Tel.: +49 211 91427-0 Internet: www.ifbs.de Detail: Verge

IFBS 4.03 187

Thickness SE Ψ [W/(m·K)] f0,25 [-] L with f0,25 < 0,7 [mm]

60 mm 0,120 0,64 51

80 mm 0,108 0,69 12

200 mm 0,050 0,81 0

IFBS 4.03 199

Annex C

Aluminium polyurethane sandwich constructions Junction details

200 IFBS 4.03

C.1 External corner (Detail 2.3.3) (IFBS 4.02 [21], Drawing 2.3.3)

Aluminium polyurethane sandwich panel

Tel.: +49 211 91427-0 Internet: www.ifbs.de Detail: External corner

IFBS 4.03 201

Thickness SE Ψ [W/(m·K)] f0,25 [-] L with f0,25 < 0,7 [mm]

60 mm - 0,036 0,89 0

80 mm - 0,036 0,92 0

200 mm - 0,036 0,96 0

C.2 External corner (Detail 2.4.1) (IFBS 4.02 [21], Drawing 2.4.1)