The Price of Thermal Bridging
January 05th, 2018
Thermal Bridging calculations can be the most cost effective way of reducing domestic carbon emissions.
What is Thermal Bridging
Thermal bridging refers to an area of a building that has a higher heat transfer than surrounding materials. These bridges often occur at junctions between elements, for example around a window. The resulting heat losses are captured by ψ-values, which are applied over the length of each junction.
How to Design for Thermal Bridging
The effect of thermal bridges can be mitigated with appropriately placed insulating materials. One approach is to follow standard details such as the BRE Accredited Construction Details. Where standard details are not used, thermal bridging calculations are required to assess the junction performance.
The bar chart shows the capital cost of these measures per tonne of carbon saved.
The cost of offset payments used in the London Plan has also been included.
In this example, use of thermal bridging calculations was by far the most cost-effective way of reducing the carbon emissions.
Ongoing Cost Savings
The solar PV system on this project was expected to pay for itself in around 19 years (accounting for export and feed in tariff payments). However when compared to carbon offsetting this reduces to around 12 years.
Assuming a base case of poor thermal bridge design (as represented by ‘default’ thermal bridging in SAP), reduced fuel bills from improved thermal design should very quickly recoup the money invested. These measures will also last the lifetime of the building, where as other technologies (such as solar PV) have a more limited service life.
Making a carbon offset payment will never give anything back so the investment stays flat.
- The use of standard construction details, or thermal bridging calculations, can provide very large carbon reductions in SAP assessments. This can result in a very cost effective route to compliance.
- Thermal bridging is particularly important for projects which fall under the London Plan 35% carbon reduction target.
- Significant ongoing cost savings may also be realised with good thermal bridge design.