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As life hots up, we can design out overheating in buildings

Words:
Ricardo Moreira

Parametric modelling can help balance light and heat in building design, and make more interesting architecture too

In August the UK had its third hottest day on record and hottest August day in 17 years. The hottest day ever was in 2019. As heat waves become more frequent, intense and lengthy, our buildings are ill-prepared to withstand them. 

Paradoxically, the fabric efficiency of new buildings makes it harder to dissipate heat, but the main challenge is that building design still underestimates overheating. London projects tend to need CIBSE TM59 modelling and analysis at planning, but this is usually seen as a compliance requirement rather than a great opportunity to improve designs. 

Alongside material choices, designing against overheating is possibly the most significant aspect within architects’ influence to make a difference in terms of climate change. 

Traditionally, environmental modelling has been compartmentalised, with energy consumption, overheating, daylight, wind, etc, all tested separately with their own performance target. Now, parametric environmental modelling helps us understand the implications of design decisions on all simultaneously, and evaluate the optimum compromises. This is especially important as energy, overheating, daylight, air quality and acoustic demands pull facade designs in different, even conflicting, directions.
A number of software tools can be used to support that effort. XCO2 uses IES extensively for detailed assessments of overheating, but as a parametric decision tool, a useful combination is Grasshopper with Honeybee for energy, daylight and overheating, and Ladybug for weather analysis, solar radiation and in-house scripts.

The parametric approach helps streamline decision-making. Using this software, we have worked with Waugh Thistleton Architects to develop an interactive tool for Pocket Living to grasp the correlation and effect of design decisions on overheating and daylight, making it easier to effect a compromise between the two and understand cost implications. The tool will be used to assess site potential during land acquisition stages, and improve thermal and daylight comfort performance in future schemes.

In general, overheating targets and methodologies are becoming more challenging, but our changing climate means that even passing the tests is no guarantee for overheating-proof real world performance – which can be modified as a result of occupant behaviour. Instead, our goal as designers should be to future-proof designs to ensure air-conditioning will not to be retrofitted into buildings. This means three things. First, facade designs must respond to their orientation (and specific solar angles), and secondly glazing should be applied selectively – and only where needed for daylight and views. There’s little benefit from glazing below 0.85m and it’s a difficult area to shade. Thirdly, external shading should be an integral part of the facade design and be considered early on. Design tools will allow us to create more precise proportions to optimize summer and winter performance.

Dare I predict a rethink of the large, portrait-shape glazing of the new London vernacular in the future? Better environmental performance should not be seen as an obstacle. It can be a positive driver for generating interesting and more diverse architecture, finding creative solutions to unique project constraints – as the most inspired architecture does. 

Ricardo Moreira is co-founder and managing director of XCO2

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