Home Features Viewpoint: retrofitting could pose thermal bridging threat

Insulation image - Knauf

Action needs to be taken to educate contractors, consultants and specifiers about bringing wall junction performance up to overall insulation standards to combat the risk of condensation build-up and mould growth within buildings, says Lee Jackson of Sustainable Building Solutions (SBS).

The team at SBS is working to raise awareness and promote solutions as a result of increased concerns that improved insulation in UK properties will result in thermal bridging issues at junctions.

Thermal bridging occurs at junctions between elements, such as windows and at interruptions in insulation. When warm internal air meets a cold surface, it can bridge the gap with cold external walls, often creating a build-up in condensation which can ultimately lead to mould growth.

When a contractor insulates a wall, a nice warm building is created, but the junction could still perform at a lower level, which in turn creates the risk of surface condensation.

Existing housing stock can have a constant bridging issue, but actions to improve the insulation, which current energy efficiency targets are likely to accelerate, increase the potential for thermal bridging with consequential implications for condensation build-up.

The SBS remedy is to improve the thermal performance of the junction in line with the rest of the wall. Modelling demonstrates that the installation of a small section of high performance insulation directly below the window sill can bring the junction up to the standards of the rest of the wall.

The window sill has to be removed as part of the insulation process. Modelling has shown that simple detailing can reduce the risk by 36 per cent over the original detailing. This is a 28.8 per cent improvement on current practise. In turn, this brings the temperature factor up to 0.927 which is 23 per cent above the recommended level.

There is clearly a need for improved levels of insulation in the UK, but it is vital that contractors and installers bring all aspects of a property’s insulation up to the highest possible standards, which includes addressing thermal bridging issues around junctions, and not just cherrypick the quick wins.

To help contractors and specifiers further, SBS launched a set of thermally-modelled standard construction drawings aimed at maximising the contribution of the new home fabric under SAP and minimising thermal conductivity.

For further information on SBS and the standard construction drawings or to download PDF copies CLICK HERE.

Lee Jackson is an expert in thermal bridging at Sustainable Building Solutions.

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