Where to Start with Thermal Bridging

What is thermal bridging?

 

It is often thought that complying with the U-values in the Part L approved document are enough.  However, achieving good fabric energy efficiency in new-build and existing homes also means designing out or minimising thermal bridging.

Thermal bridging occurs at the junctions where, for example, the wall meets the floor; or where components cut through the insulation layer, such as windows in a wall.

The risks when thermal bridging is not addressed are:

  • Poor energy efficiency
  • Condensation
  • Mould growth

 

Calculating thermal bridging

 

When assessing the energy performance of a dwelling, SAP (Standard Assessment Procedure) is used. Each individual thermal bridge has to be input into the assessment and when combined these have a significant effect on SAP scores. When inputting the thermal bridging there are three options:

  1. Default Values.

Default thermal bridge values can be used but they assume a worst-case. If used improvements have to made elsewhere to overcome their shortcomings.

  1. Accredited Construction Details (ACD’s)

These are generic details for common construction junctions which were approved by the DCLG (now the Ministry of Housing) in 2007. They have better than default values and have been relied upon by many designers to comply with Part C and Part L of the Building Regulations.

  1. Calculated Thermal Bridges

We can calculate the thermal bridging heat loss for you, so that the SAP assessor can use a bespoke Ψ-value for your construction details, and you can be confident that the junction meets the condensation/mould growth requirements in the Building Regulations.

The ability to use Accredited Construction Details is being removed in the near future to encourage precise assessments for each project. So, unless calculated values are used the default values will be assumed in SAP assessments meaning improvements will need to be made elsewhere.

If you’re thinking about having thermal bridging calculated, here a few things to think about.

 

1. Thermal bridging for different types of construction

 

A building element can have repeating thermal bridges which have a significant effect on the heat flow, such as steel studs within the insulation layer, and sometimes the repeating thermal bridges can be ignored for the purposes of the thermal bridging calculation.  We can give you guidance on this.

Good section drawings that show the construction of the building elements enable us to model the heat flow as accurately as possible.  Good details to include are:

  • Thickness and dimensions of the repeating bridge
  • Centres of any repeating components

 

2. Proprietary Products or Systems

 

The biggest advantage to a bespoke thermal bridging calculation over a generic construction detail is that we can model the construction detail that you are designing, not a worst-case similar, generic detail.

We don’t expect you to know all the technical data for any proprietary products that you are specifying, but if you can supply any information that you have, we can usually obtain any additional technical data that we need to include your specified products in the model.  Such information that we need from you are:

  • Manufacturer name;
  • Product name;
  • Any product codes to identify a specific component.

Although we would obviously like you to use our insulation products, don’t worry if you have not specified these in your details.  We offer thermal bridging calculations as a technical consultancy service, and we will still provide you with the calculations that you need even if our products are not specified.

 

3. Performance Targets

 

We can just calculate the thermal bridging heat loss and condensation risk for your supplied details, although we would prefer to help you meet your aims and objectives.

If you tell us more about the problem that you’re trying to solve or what you are looking to achieve, we can advise on the best way to reduce the effect of thermal bridging and limit the quantity of calculations required.

Our technical team are specialists in using reflective foil insulation products, and we can give expert advice on how reflective foil insulation can be used to optimise the thermal performance of construction junctions; Improving the building fabric energy efficiency and limit the risk of surface condensation and mould growth.

Give our technical team a call on 01582 544255 or email us at [email protected] if you would like help with your thermal bridging calculations.