Matthew Brooke-Peat BSc (Hons) MSc CEnv MCIOB MCIAT LCGI

Thermal Bridging

Rev B 2015

Introduction Content

This lecture will:

• Identify fabric heat transfer paths

• Explain the concept of thermal bridging

• Illustrate the types of thermal bridges

• Cover the requirements under Building

Regulations Part L

• Provide examples of thermal bridges using

case studies

Fabric Heat Transfer Paths

• Plane elements

• Thermal bridges

• Air permeability (not covered in this lecture)

• Thermal Bypasses (should be designed out)

Fabric Heat Transfer Paths

Thermal bridges

Plane elements

+ Air permeability

𝐻 = 𝐴×𝑈 + ℓ×Ψ+ χ

Fabric Heat Transfer Heat Transmission Coefficient

Plane elements Point thermal bridges

Linear thermal bridges

(W/K)

Plane Elements U-value

U-value (W/m2K)

Thermal Bridges Repeating and Non-repeating

Non-repeating

thermal bridge

Repeating

thermal bridge

Thermal Bridges Linear

Ψ-value (W/mK)

Thermal Bridges Point

χ-value (W/K)

Thermal Bridges Geometric

Thermal Bridge

Plane elements

Thermal Bridges Geometric

Thermal Bridges Constructional

Plane elements

Thermal Bridges Constructional

Thermal Bridges Temperature Factors

• Used to assess risk of surface condensation or

mould growth

• Based on lowest surface temperature (Tsi)

• Expressed as ƒRsi

• Must be > ƒCRsi in BR IP 1/06

ƒ𝑅𝑠𝑖 =𝑇𝑠𝑖 − 𝑇𝑒𝑇𝑖 − 𝑇𝑒

Building Regulations Part L Requirements

• Insulation must be reasonably continuous over

whole building envelope

• No reasonably avoided thermal bridges in

insulation layers

Building Regulations Part L Options

• Accredited Construction Details

• Numerical Modelling (thermal modelling)

• No specific quantification of thermal bridges

• A mixed approach is permitted

Building Regulations Part L Approved Design Details

• Approved Design Details set out by DCLG or

recognised by DCLG

• Builder must demonstrate that an appropriate

system of site inspection is in place

Building Regulations Part L Thermal Modelling

• Calculated by a person with suitable expertise

and experience

• In accordance with BR 497

• Builder must demonstrate that an appropriate

system of site inspection is in place

Building Regulations Part L No Specific Quantification

• Default Ψ-values from SAP

• Use default y-value of 0.15

Building Regulations Part L National Calculation Methodology

• The Government’s Standard Assessment

Procedure (SAP)

• Simplified Building Energy Model (SBEM)

• Dynamic Simulation Modelling (DSM)

Building Regulations Part L National Calculation Methodology

𝐻𝑇𝐵 = ℓ ×Ψ

𝐻𝑇𝐵 = 𝑦 𝐴𝑒𝑥𝑝

𝑦 =ℓ × Ψ

𝐴𝑒𝑥𝑝

Single parameter used where values for individual bridges are not used

Aexp = Total heat loss area (m2)

Code for Sustainable Homes

• CSH assessment informed by SAP

• Category 1: Energy and Carbon Dioxide

Emissions

• Dwelling CO2 Emissions Rate (DER)

• Fabric Energy Efficiency (FEE)

Building Regulations Part L

Normal Corner

Design Case Study

This case study will:

• Demonstrate the effect on thermal bridging

when increasing the levels of insulation to a

normal corner

Normal Corner

Design Case Study

• Insulation λ = 0.020 W/mK

• 50mm insulation in base model

• Increased to 75mm and 100mm

Normal Corner: U-values

Design Case Study

Insulation

Thickness: Increase: U-value (W/m2K): Improvement:

50 0.27

75 50% 0.21 22%

100 100% 0.17 37%

Based on Blocks λ = 0.110 W/mK

Normal Corner: Ψ-values

Design Case Study

Insulation

Thickness: Increase: Ψ (W/mK): Improvement:

50 0.052

75 50% 0.043 16%

100 100% 0.038 27%

Based on Blocks λ = 0.110 W/mK

Normal Corner: 50mm Insulation Temperature Gradient

Design Case Study

Normal Corner: 75mm Insulation Temperature Gradient

Design Case Study

Normal Corner: 100mm Insulation Temperature Gradient

Design Case Study

Normal Corner: Temperature Factors

Design Case Study

Insulation

Thickness: Increase: ƒRsi: Improvement:

50 0.957

75 50% 0.967 1%

100 100% 0.973 2%

Forensic Case Study 1 Lintel Detail

Forensic Case Study 1 Lintel Detail

ƒCRsi = 0.750

ƒRsi = 0.671

Risk of surface condensation

and mould growth

Exceeds

Regulatory

limit

Forensic Case Study 2 Jamb Detail

Forensic Case Study 2 Jamb Detail

Default = 0.100 W/mK

ADD = 0.050 W/mK

TM = 0.064 W/mK

Summary

This lecture has:

• Identified fabric heat transfer paths

• Explained the concept of thermal bridging

• Illustrated the types of thermal bridges

• Covered the requirements under Building

Regulations Part L

• Provided examples of thermal bridges using

case studies

Questions

?

References

Anderson, B. (2006) Conventions for U-value Calculations. BR 443. Watford: Building Research Establishment.

Building Research Establishment. (2011) National Calculation Methodology (NCM) Modelling Guide (for Buildings Other

than Dwellings in England and Wales). Watford: Building Research Establishment.

Department for Communities and Local Government. (2010) Code for Sustainable Homes Technical Guide. London: RIBA

Publishing.

Department for Communities and Local Government. (2007) Accredited Construction Details. Wetherby, Communities and

Local Government Publications.

Department of Energy and Climate Change. (2013) SAP 2012: The Government’s Standard Assessment Procedure for

Energy Rating of Dwellings. Watford: Building Research Establishment.

Energy Saving Trust. (2008) Enhanced Construction Details: Introduction and Use. CE297. London: Energy Saving Trust.

Energy Saving Trust. (2009) Enhanced Construction Details: Thermal Bridging and Airtightness. CE302. London:

Energy Saving Trust.

HM Government. (2013) Approved Document L1A: Conservation of Fuel and Power in New Dwellings. The Building

Regulations 2010. London: NBS.

Ward, T. & Sanders, C. (2007) Conventions for Calculating Linear Thermal Transmittance and Temperature Factors.

BR 497. Watford: Building Research Establishment.

Ward, T. (2006) Assessing the Effects of Thermal Bridging at Junctions and Around Openings. IP 1/06. Watford:

Building Research Establishment.