Hygrothermal performance of Supalite Revised Roof system · 2020. 12. 23. · 3 BS EN ISO 13788:2012, ‘Hygrothermal performance of building components and building elements –

Hygrothermal performance of Supalite Revised Roof system

Calculations to BS EN 15026 using WUFI modelling software

Prepared for: Steven Hacking

Date: 20 November 2017

Report Number: P108467-1010

BRE Wales & SW Ethos Kings Road Swansea SA1 8AS Customer Services 0333 321 8811 T + 44 (0) 1792 630100 F + 44 (0) 1792 630101 E [email protected]

Prepared for: Steven Hacking SupaLite Tiled Roof System Ltd. 180-181 Bradkirk Place Walton Summit Preston PR5 8AJ

Hygrothermal performance of revised Supalite Tiled Roofing system

Commercial in Confidence

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© Building Research Establishment Ltd

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This report is made on behalf of Building Research Establishment Ltd. (BRE) and may only be distributed in its entirety, without amendment, and with attribution to BRE to the extent permitted by the terms and conditions of the contract. BRE’s liability in respect of this report and reliance thereupon shall be as per the terms and conditions of contract with the client and BRE shall have no liability to third parties to the extent permitted in law.

Prepared by

Name Dr Caroline Weeks

Position Senior Consultant

Date 16 November 2017

Signature

Authorised by

Name Colin King

Position Director, BRE Wales

Date 20 November 2017

Signature



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BRE have been commissioned by Supalite Tiled Roofing Systems to model their proposed revised conservatory system using WUFI Pro v6 hygrothermal modelling software. The WUFI software was created by the Fraunhofer Institute in Germany and can be used to assess the Hygrothermal performance of building components in accordance with BS EN 15026:2007. WUFI software is widely accepted as offering a more realistic assessment of the potential risk of failure due to moisture accumulation within building components based on this standard rather than traditional steady state calculations, such as those used in the Glaser method or BS EN ISO 13788:2012.

Analysis has been carried out for 6 example climate locations across the UK, including:

• London

• Manchester

• Bristol

• Swansea

• Aberdeen

• Edinburgh

The results indicate that there is no risk of interstitial or surface condensation forming in the structure at any of the tested locations. However, conditions may give rise to mould growth at the internal surface, with Aberdeen being the worst location scenario for this.

It should be noted that a relatively ‘worst case’ environmental condition has been assumed for this modelling (i.e. high relatively humidity as a result of poor ventilation), which is unfortunately a relatively common occurrence throughout buildings in the UK. Supalite Tiled Roofing Systems Ltd may therefore wish to give consideration to the internal finishes used for the roof system and advise on an appropriate cleaning regime to reduce the risk of dirt accumulation exacerbating potential mould growth at the internal roof surface. While risk would also be reduced if ventilation were adequate and sufficient to keep the RH well below 80%, it is acknowledged that ventilation provision is essentially beyond Supalite Tiled Roofing Systems Ltd’s control as a roof supplier.

Executive Summary



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Table of Contents

1 Introduction 4 2 Description of the modelling 6

2.1 Modelling parameters 6

2.2 Regional climate analysis 8

3 Findings 12

3.1 London 12

3.1.1 Interstitial condensation 12 3.1.2 Surface Condensation and mould risk 13

3.2 Manchester 16


3.3 Bristol 20


3.4 Swansea 24


3.5 Aberdeen 28


3.6 Edinburgh 32


4 Conclusions 36 5 References 37



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1 Introduction

BRE have been commissioned by Supalite Tiled Roofing Systems Ltd to model their proposed revised conservatory system using WUFI Pro hygrothermal modelling software1. The WUFI software was created by the Fraunhofer Institute in Germany and can be used to assess the Hygrothermal performance of building components in accordance with BS EN 15026:20072 if specific material properties are known.

The minimum data requirements for materials are:

• Bulk density [kg/m³],

• Porosity [m³/m³],

• Heat capacity [J/kgK],

• Thermal conductivity (dry, 10°C) [W/mK],

• Vapour resistance factor dry [-],

The benefit of using WUFI is that the programme allows the calculation of condensation and mould spore risk under dynamic conditions using the actual physical material properties and climate conditions according to the proposed location(s) of the building element. This helps to overcome the inherent weaknesses of undertaking condensation risk analysis using only steady state calculations, such as those used in the Glaser method or BS EN ISO 13788:20123. The WUFI software is widely accepted as offering a more realistic condensation risk analysis based on BS EN 15026:2007 to assess the potential risk of failure due to moisture accumulation within building components.

For this modelling, 6 cities have been chosen to represent a range of locations across the UK:

Zone 1 – London

Zone 2 – Manchester

Zone 3 – Bristol

Zone 4 – Swansea

Zone 5 – Aberdeen

Zone 6 – Edinburgh

1 WUFI Pro version 6 – Hygrothermal modelling software, Fraunhofer Institute

2 BS EN 15026:2007, ‘Hygrothermal performance of building components and building elements – Assessment of moisture transfer by numerical simulation, BSI, 2007

3 BS EN ISO 13788:2012, ‘Hygrothermal performance of building components and building elements – Internal surface temperature to avoid critical surface humidity and interstitial condensation – Calculation methods’, BSI, 2012



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The typical roof construction is shown in Figure 1. The modelling is based on construction through the bulk of the element, as indicated by the red arrow.

Figure 1: Typical Proposed revised conservatory construction



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2 Description of the modelling

The following methodology is used for the assessment:

Step 1 – Specific material properties supplied by Supalite Roofing Systems Ltd

Step 2 – Create material profiles useable by WUFI from data provided

Step 3 – Creation of weather files to simulate relative exposure and levels of wind driven rain for 6 locations across the UK using Meteonorm 7 software

Step 4 – Create the construction build up

Step 5 – Set parameters for the models

Step 6 – Run analysis calculations

Step 7 – Run analysis diagnostics

For any given model period, a number of parameters should be met for the calculation to be deemed acceptable in terms of condensation risk (interstitial and surface):

• The total moisture content at any location should not increase year on year

• The relative humidity (RH) of the structure should decrease to below 80% within the first 6 months of the modelling period and not exceed 80% for extended periods at any other time

• No reported critical convergences in the calculation (moisture present in the structure, where not anticipated) at any location

2.1 Modelling parameters Table 1 shows the material properties assumed for the construction elements in the modelling, as informed by the client, while Figure 2 shows the make-up of the construction, as represented in WUFI.

Table 1: Material properties used for the analysis



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Figure 2: Construction makeup within WUFI



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• The model grid (effectively the number of calculation steps) uses WUFI’s automatic (II) medium grid.

• Initial moisture and temperature conditions are assumed to be constant across the component at 80% RH and 20ºC respectively. 80% RH is typically reached in cases of poor ventilation, which are unfortunately quite common across the UK. Hence, this is a relatively conservative assessment approach.

• The condensation analysis models are run for a minimum period of 5 years. If a model has not stabilised within this time the modelling period is extended to 10 years. If the model still does not stabilise after a 10 year simulation then interstitial and/ or surface condensation would be inevitable, indicating the structure as being unsuitable in the location(s) indicated by the climate models.

• Orientation is set to the most severe direction for wind driven rain, determined according to the respective weather files (see below). Roof inclination is taken to be 20º.

• Heat resistances at the external and internal surfaces use the WUFI default for roofs. Short-wave radiation absorptivity is assumed for a ‘dark’ coloured surface. The fraction of adhering rain on the surface is dictated by the component inclination, as indicated above.

2.2 Regional climate analysis Analysis of the weather files in the following figures for the 6 chosen city locations indicates that the prevailing driving rain direction for the majority of the locations is from the south west (or south, south west in some cases), while the prevailing direction for Swansea is from the west. All models have subsequently been run assuming the construction faces south west, except for Swansea which is run facing west.



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Figure 3: London weather analysis

Figure 4: Manchester weather analysis



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Figure 5: Bristol weather analysis

Figure 6: Swansea weather analysis



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Figure 7: Aberdeen weather analysis

Figure 8: Edinburgh weather analysis



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3 Findings

3.1 London Figure 9 shows the cross section through the roof structure based on London climate data. The upper chart (red) shows temperature, the lower chart (green) shows RH and water content (blue). The solid colour sections show the upper and lower value ranges experienced over the whole 5-year cycle period. The thick coloured lines show the average value over the cycle period. The model showed no ‘convergence’ errors, suggesting good calculation accuracy and no points of moisture saturation within the model (which can give rise to convergence errors). (Table 2 at end of section).

Figure 9: Whole structure analysis based on London climate

3.1.1 Interstitial condensation It can be seen that the majority of the roof structure remains below 80% RH over the 5-year cycle period. However, the inner plasterboard and plaster layers exceed this value on occasion and the average RH at the surface is approximately 78%. The blue line representing average water content remains at a low level throughout the cycle; there are no spikes in the presence of moisture at material interfaces, suggesting there is no risk of interstitial condensation forming between layers, confirmed by the lack of



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notable convergence errors in the calculation. The moisture content increases slightly at the inner surface, as shown by the light blue area at the bottom right of the graph. This occurs periodically throughout each cycle year and is not simply a result of initial drying out.

Figure 10 shows how the total water content in the model changes over the monitoring cycle. It can be seen that the initial moisture level drops after the first 6 months and then reaches a dynamic equilibrium, i.e. the total moisture content does not increase year on year, confirming that any moisture within the structure follows natural seasonal cycles and does not increase over time.

Figure 10: Total water content across the structure over 5-year cycle period (London)

3.1.2 Surface Condensation and mould risk The analysis of the London model in Figure 9 suggests that the inner surface may experience elevated RH and increased surface moisture content. More detailed analysis of the internal temperature versus the dew point of the internal surface, as shown in Figure 11, shows that the temperatures track each other but do not converge, suggesting that internal surface condensation should not occur. However, moisture may still be present in the surface to facilitate mould growth.

Further analysis in WUFI Bio software, which analyses the risk of mould, shows a green signal (of a ‘traffic light’ system) when assessing ‘class II’ substrates (Figure 12). These include surfaces such as plaster with a low ‘biological’ component. When assessed against ‘class I’ substrates, the analysis shows an amber warning, suggesting some mould growth may occur. Class I includes material substrates with biological components on which mould can feed, including wall paper, plasterboard, or even just the build-up of dirt/ contaminants.

The internal finish of the roof system is therefore an important consideration and at the very least an appropriate cleaning regime should be recommended to reduce the risk of dirt accumulation leading to mould. Risk would also be reduced if ventilation were adequate and sufficient to keep the RH well below 80%.



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Figure 11: Temperature and dew point at the internal surface of the construction (London)

Figure 12: WUFI bio assessment of mould growth on Class II internal surfaces (London)



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Table 2: Final report from WUFI calculation (London)



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3.2 Manchester Figure 13 shows the cross section through the roof structure based on Manchester climate data. The upper chart (red) shows temperature, the lower chart (green) shows RH and water content (blue). The solid colour sections show the upper and lower value ranges experienced over the whole 5-year cycle period. The thick coloured lines show the average value over the cycle period. The model showed no ‘convergence’ errors, suggesting good calculation accuracy and no points of moisture saturation within the model (which can give rise to convergence errors). (Table 3 at end of section).

Figure 13: Whole structure analysis based on Manchester climate

3.2.1 Interstitial condensation It can be seen that the majority of the roof structure remains below 80% RH over the 5-year cycle period. However, the inner insulation, plasterboard and plaster layers exceed this value on occasion and the average RH at the surface is approximately 82%. The blue line representing average water content remains at a low level throughout the cycle; there are no spikes in the presence of moisture at material interfaces, suggesting there is no risk of interstitial condensation forming between layers, confirmed by the lack of notable convergence errors in the calculation. The moisture content increases slightly at the inner surface, as shown by the light blue area at the bottom right of the graph. This occurs periodically throughout each cycle year and is not simply a result of initial drying out.



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Figure 14: Total water content across the structure over 5-year cycle period (Manchester)

3.2.2 Surface Condensation and mould risk The analysis of the Manchester model in Figure 13 suggests that the inner surface may experience elevated RH and increased surface moisture content. More detailed analysis of the internal temperature versus the dew point of the internal surface, as shown in Figure 15, shows that the temperatures track each other but do not converge, suggesting that internal surface condensation should not occur. However, moisture may still be present in the surface to facilitate mould growth.

Further analysis in WUFI Bio software, which analyses the risk of mould, shows an amber signal (of a ‘traffic light’ system) when assessing ‘class II’ substrates, suggesting some mould growth may occur (Figure 16). These include surfaces such as plaster with a low ‘biological’ component. When assessed against ‘class I’ substrates, the analysis shows a red warning, suggesting significant mould growth may occur, which would not normally be considered acceptable. Class I includes material substrates with biological components on which mould can feed, including wall paper, plasterboard, or even just the build-up of dirt/ contaminants.

The internal finish of the roof system is therefore an important consideration and at the very least an appropriate cleaning regime should be recommended to remove the potential for dirt accumulation leading to mould. Risk would also be reduced if ventilation were adequate and sufficient to keep the RH well below 80%.



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Figure 15: Temperature and dew point at the internal surface of the construction (Manchester)

Figure 16: WUFI bio assessment of mould growth on Class II internal surfaces (London)

Table 3: Final report from WUFI calculation (Manchester)



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3.3 Bristol Figure 17 shows the cross section through the roof structure based on Bristol climate data. The upper chart (red) shows temperature, the lower chart (green) shows RH and water content (blue). The solid colour sections show the upper and lower value ranges experienced over the whole 5-year cycle period. The thick coloured lines show the average value over the cycle period. The model showed no ‘convergence’ errors, suggesting good calculation accuracy and no points of moisture saturation within the model (which can give rise to convergence errors). (Table 4 at end of section).

Figure 17: Whole structure analysis based on Bristol climate

3.3.1 Interstitial condensation It can be seen that the majority of the roof structure remains below 80% RH over the 5-year cycle period. The inner plasterboard and plaster layers exceed this value on occasion but the average RH at the surface is approximately 76%. The blue line representing average water content remains at a minimum level throughout the cycle; there are no spikes in the presence of moisture at material interfaces, suggesting there is no risk of interstitial condensation forming between layers, confirmed by the lack of notable convergence errors in the calculation. The moisture content increases slightly at the inner surface, as shown by the light blue area at the bottom right of the graph. This occurs periodically throughout each cycle year and is not simply a result of initial drying out.



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Figure 18: Total water content across the structure over 5-year cycle period (Bristol)

3.3.2 Surface Condensation and mould risk The analysis of the Bristol model in Figure 17 suggests that the inner surface may experience elevated RH and increased surface moisture content. More detailed analysis of the internal temperature versus the dew point of the internal surface, as shown in Figure 19, shows that the temperatures track each other but do not converge, suggesting that internal surface condensation should not occur. However, moisture may still be present in the surface to facilitate mould growth.





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Figure 19: Temperature and dew point at the internal surface of the construction (Bristol)

Figure 20: WUFI bio assessment of mould growth on Class II internal surfaces (Bristol)

Table 4: Final report from WUFI calculation (Bristol)



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3.4 Swansea Figure 21 shows the cross section through the roof structure based on Swansea climate data. The upper chart (red) shows temperature, the lower chart (green) shows RH and water content (blue). The solid colour sections show the upper and lower value ranges experienced over the whole 5-year cycle period. The thick coloured lines show the average value over the cycle period. The model showed no ‘convergence’ errors, suggesting good calculation accuracy and no points of moisture saturation within the model (which can give rise to convergence errors). (Table 5 at end of section).

Figure 21: Whole structure analysis based on Swansea climate

3.4.1 Interstitial condensation It can be seen that the majority of the roof structure remains below 80% RH over the 5-year cycle period. The inner insulation, plasterboard and plaster layers exceed this value on occasion but the average RH at the surface is approximately 82%. The blue line representing average water content remains at a minimum level throughout the cycle; there are no spikes in the presence of moisture at material interfaces, suggesting there is no risk of interstitial condensation forming between layers, confirmed by the lack of notable convergence errors in the calculation. The moisture content increases at the inner surface more so than the climate locations above, as shown by the light blue area at the bottom right of the graph. This occurs periodically throughout each cycle year and is not simply a result of initial drying out.



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Figure 22 shows how the total water content in the model changes over the monitoring cycle. It can be seen that the initial moisture level drops after the first 6 months and then reaches a dynamic equilibrium, i.e. the total moisture content does not increase year on year, confirming that any moisture within the structure follows natural seasonal cycles and does not increase over time. The peaks experienced due to the Swansea climate are higher than experienced in the other climate locations above.

Figure 22: Total water content across the structure over 5-year cycle period (Swansea)

3.4.2 Surface Condensation and mould risk The analysis of the Swansea model in Figure 21 suggests that the inner surface may experience elevated RH and increased surface moisture content. More detailed analysis of the internal temperature versus the dew point of the internal surface, as shown in Figure 23, shows that the temperatures track each other but do not converge, suggesting that internal surface condensation should not occur. However, moisture may still be present in the surface to facilitate mould growth.





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Figure 23: Temperature and dew point at the internal surface of the construction (Swansea)

Figure 24: WUFI bio assessment of mould growth on Class II internal surfaces (Swansea)

Table 5: Final report from WUFI calculation (Swansea)



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3.5 Aberdeen Figure 25 shows the cross section through the roof structure based on Aberdeen climate data. The upper chart (red) shows temperature, the lower chart (green) shows RH and water content (blue). The solid colour sections show the upper and lower value ranges experienced over the whole 5-year cycle period. The thick coloured lines show the average value over the cycle period. The model showed no ‘convergence’ errors, suggesting good calculation accuracy and no points of moisture saturation within the model (which can give rise to convergence errors). (Table 6 at end of section).

Figure 25: Whole structure analysis based on Aberdeen climate


Figure 26 shows how the total water content in the model changes over the monitoring cycle. It can be seen that the initial moisture level drops after the first 6 months and then reaches a dynamic equilibrium,



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i.e. the total moisture content does not increase year on year, confirming that any moisture within the structure follows natural seasonal cycles and does not increase over time.

Figure 26: Total water content across the structure over 5-year cycle period (Aberdeen)

3.5.2 Surface Condensation and mould risk The analysis of the Aberdeen model in Figure 25 suggests that the inner surface may experience elevated RH and increased surface moisture content. More detailed analysis of the internal temperature versus the dew point of the internal surface, as shown in Figure 27, shows that the temperatures track each other but do not converge, suggesting that internal surface condensation should not occur. However, moisture may still be present in the surface to facilitate mould growth.





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Figure 27: Temperature and dew point at the internal surface of the construction (Aberdeen)

Figure 28: WUFI bio assessment of mould growth on Class II internal surfaces (Aberdeen)



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Table 6: Final report from WUFI calculation (Aberdeen)



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3.6 Edinburgh Figure 29 shows the cross section through the roof structure based on Edinburgh climate data. The upper chart (red) shows temperature, the lower chart (green) shows RH and water content (blue). The solid colour sections show the upper and lower value ranges experienced over the whole 5-year cycle period. The thick coloured lines show the average value over the cycle period. The model showed no ‘convergence’ errors, suggesting good calculation accuracy and no points of moisture saturation within the model (which can give rise to convergence errors). (Table 7 at end of section).

Figure 29: Whole structure analysis based on Edinburgh climate


Figure 30 shows how the total water content in the model changes over the monitoring cycle. It can be seen that the initial moisture level drops after the first 6 months and then reaches a dynamic equilibrium,



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i.e. the total moisture content does not increase year on year, confirming that any moisture within the structure follows natural seasonal cycles and does not increase over time.

Figure 30: Total water content across the structure over 5-year cycle period (Edinburgh)

3.6.2 Surface Condensation and mould risk The analysis of the Edinburgh model in Figure 29 suggests that the inner surface may experience elevated RH and increased surface moisture content. More detailed analysis of the internal temperature versus the dew point of the internal surface, as shown in Figure 31, shows that the temperatures track each other but do not converge, suggesting that internal surface condensation should not occur. However, moisture may still be present in the surface to facilitate mould growth.





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Figure 31: Temperature and dew point at the internal surface of the construction (Edinburgh)

Figure 32: WUFI bio assessment of mould growth on Class II internal surfaces (Edinburgh)



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Table 7: Final report from WUFI calculation (Edinburgh)



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4 Conclusions

Condensation risk has been modelled for the revised Supalite Roof structure using WUFI hygrothermal modelling software according to the dynamic modelling standard BS EN 15026:2007 for 6 locations across the UK.

Based on the material properties and roof design provided for the analysis:

• Moisture content within the structure reduces after the first 6 months of the model and does not increase year on year in any location

• There are no convergence failures within the calculations and no indication of moisture accumulation at any interface within the structure, suggesting there should be no risk of interstitial condensation forming in any of the tested UK locations

• The internal surface temperature of the construction does not converge with the predicted dew point at any time, suggesting that surface condensation should not occur in any of the tested UK locations

• Moisture was indicated to be present within the internal surface layer of the construction at intermittent periods over the 5-year cycle in all UK locations, even though the average moisture content was low.

• Mould spore growth analysis using the WUFI Bio extension tool indicated that for Class II surface substrates, such as plaster, mould growth would be relatively inconsequential in London, but mould would be likely in all other tested locations.

• When Class I surface substrates were considered, which could include the accumulation of dirt/ contaminants at the surface, mould growth would be likely in London and mould would be deemed unacceptable in all other tested locations.

• The Aberdeen climate location showed the highest risk and incidence of mould growth at the internal surface of the construction.

• The internal finish of the roof system is therefore an important consideration and at the very least an appropriate cleaning regime should be recommended to remove the potential for dirt accumulation on the inner construction surface that could lead to mould growth.

• Risk would also be reduced if ventilation were adequate and sufficient to keep the RH well below 80%, although the worst case Aberdeen climate experienced an average RH of only 70%, emphasising that it may be only relatively short bursts of high humidity that can exacerbate the risk of mould growth. It is acknowledged that ventilation provision is generally beyond the control of Supalite Ltd as a roof supplier.

The models have been undertaken with a predicted good level of construction and with no air gaps or defects across the components. Should the level of construction not be of adequate quality or any defects in the structure are no repaired to the standard specified by the manufacturer, these models cannot be used an indication of the performance of the proposed roof.



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5 References

WUFI – Wärme und Feuchte instationär, Transient Heat and Moisture Software for calculating the coupled heat and moisture transfer in building components, Fraunhofer Institute

BS EN 15026:2007, ‘Hygrothermal performance of building components and building elements – Assessment of moisture transfer by numerical simulation, BSI, 2007

BS EN ISO 13788:2012, ‘Hygrothermal performance of building components and building elements – Internal surface temperature to avoid critical surface humidity and interstitial condensation – Calculation methods’, BSI, 2012

Documents

Hygrothermal performance of Supalite Revised Roof system · 2020. 12. 23. · 3 BS EN ISO 13788:2012, ‘Hygrothermal performance of building components and building elements –