Minimising Heat Loss in Residential Buildings
With the ever-increasing spotlight on the thermal performance of a building, it has become more and more important to address issues of minimising heat loss. This need is heightened in the face of climate crisis around the world. Thermal performance in buildings is hugely important, particularly in the drive to reduce a building’s carbon footprint in both construction and operation.
Balancing heat loss with other design considerations
There are two elements to addressing and minimising heat loss and thermal bridging in a building. The first is to reduce the number of connections and penetrations from the outside through to the inside. The second is to question what impact those penetrations have on internal surface temperatures that could lead to mould and condensation issues.
An ideal façade would be one unbroken line with no balconies, as the more penetrations through a façade, the more potential for heat loss and cold spots (which can cause condensation or mould damage). But, of course, that is not always possible, and balconies are desirable for all sorts of other reasons. The aim, therefore, is to reduce the heat loss per penetration as well as keeping the number of penetrations to a minimum. These two must be carefully balanced; fewer, larger penetrations may be worse.
The importance of thermal bridging
There are lots of projects in medium and high-rise buildings where thermal bridging has not been adequately considered, but it is absolutely key in mitigating heat loss from a building. The Aqua Tower in Chicago is a prime example of extreme thermal bridging with continuous concrete slabs and windows butted up against them and the measures of heat loss are enormous.
In many buildings a U-value has been applied across the whole of the building without considering all the penetrations throughout it. Areas where heat loss is at its greatest are windows, where windows butt up against walls and where balconies butt up against a façade without thermal break. All these can have an enormous impact on thermal performance. On paper you can have a low U-value that has been calculated from the middle of a wall where there are no penetrations, without considering the areas where there are penetrations. When not adequately assessed, costs can be unmanageable.
Testing heat loss in buildings
How we measure heat loss and collate the data, informs architects and designers on the best ways to minimise heat loss in future designs. Understanding the likely heat loss can be done in three ways:
- Using simulations and risk analysis, from past data and buildings of a similar design
- Testing individual materials in the lab and extrapolating from there
- Site tests once the building is complete.
The last of these can yield powerful insights but testing of a finished building usually means it is too late to make changes to that building. Best practice is to consider heat loss at the design stage and choose design elements which minimise the total thermal bridging to save on design, construction and end user costs – and to undertake post-completion testing to verify the design decisions.
This article is based on an interview with Toby Cambray, Building Physicist, Engineer and Director at Greengauge.