Should overheating be driving residential design? Carbon Vs Comfort

Summer is over, and we miss it already, but one thing I’m sure we consensually do not miss is trying to sleep when its sweltering inside and outside, with no aircon and no cool airflow even with the windows open. Hurley Palmer Flatt’s Divisional Director, Paul Scriven and Associate Director, Annie Marston teamed up to discuss this pressing matter in the residential sector.

The seminar ‘Should Overheating be Driving Residential Design? Carbon vs Comfort‘ started with the question to the audience ‘how many people here have experienced discomfort in their own home?’. To this the vast majority of hands shot up into the air.

Trends in design are constantly changing with windows being larger than ever, infiltration at its lowest, and cooling techniques having shifted from opening a window to air conditioning. Passive design that takes advantage of the climate to maintain a comfortable temperature range in the home, allowing nature in, is no more, instead active design has arisen as a modern approach which keeps nature out. We have very pleasant environment outside, yet we keep sealing it out.

With fuel resources dwindling we need to use less and think about alternative ways to lighten our usage. Compliance has been pushing carbon savings (100% carbon zero for residential buildings in London GLA), as well as rising g-values to encourage more solar gain in winter, and higher levels on insulation which means more heat is trapped inside the building. Less heating equals less carbon, however, these measures tend to trap hot air in buildings in the summer, so carbon is prioritised over comfort and the need for lessened demand is paramount. With this in mind there is a need for legislation to be driven by the government to push the saving of resources, because unless you force people to do something they generally won’t do it.

So, bringing it back to the residential sector, why should we be worried about overheating in residential buildings?

Not only is active design heating up housing interiors, but we also have more technology than ever which emits heat into our homes. Not forgetting that the world is constantly heating up!

Overheating, firstly, has health risks. King’s College London and the Met Office predicted the number of heat-related deaths will quadruple in cities such as London by 2080. For a landlord there are multiple issues: complaints where tenants individually or as a group come together to demand AC, which will be expensive; building and rental values going down due to lack of cooling system and also word of mouth about the bad conditions; and future proofing as policy dictating overheating standards needing to be met before the rent / sale. Wouldn’t it be great if EPCs came with a risk analysis of overheating?

There are overheating assessments that can be put into place, however, most of these are optional. The Compliance assessment Part L, SAP and SBEM are compulsory, unlike the Green Certification which is an optional assessment type. Guides such as CIBSE Guide A and ASHRAE 55 also come as optional. Thus, implementation needs to be put in place to make this a necessity in residential buildings. The London Plan (2016) expects TM59 Overheating risk in Residential buildings to be done, this guidance was released in 2018.

At what point should be overheating be assessed in design?

The answer is early and throughout to avoid errors and expensive amendments to fix the issue which will most likely arise. The stages and solutions can be looked at in the form of a life-cycle:

• Masterplanning – solar mapping, mass and form
• Conceptual design – façade optimisation, mass and form, solar mapping
• Preplanning – detailed comfort, pre-assessments BREEAM and LEED, TM59/49
• Design Development – TM52&59&49 over heating assessments, Part L compliance, BREEAM, LEED, WELL
• Construction – value engineering assessments, contractors’ requests
• Post occupancy – building control, occupant complaints
• Decommissioning

And then back round the circle.

Mitigation techniques need to be assessed in design, in elements such as the heat transfer through different materials, the use of blinds and louvres, and natural ventilation techniques that avoid negative variables such as pollution, dust and noise.

A suggestion of Hurley Palmer Flatt, to avoid problems arising within planning and to analyse mitigation techniques, is to bring in a Building Physicist to work between the Building Service Consultant and Architect. It is the responsibility of everyone involved to ensure that overheating in residential buildings is avoided, it is a problem which will only get worse if nothing is done.

Credit: Original Video can be located at