Are overheating homes really a disaster waiting to happen?

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Professor Kevin Lomas of Loughborough University has warned that the UK is facing a public health disaster if the issue of overheating in homes is not tackled.

While overheating in homes is a growing concern and something we must address,is it the biggest issue facing the UK’s housing stock and that ‘new homes being heavily insulated to meet environmental targets’ are to blame.

At present, it’s thought that there are 25,000 deaths linked to cold weather per year in the UK, while excess heat due to high outdoor temperatures causes around 2,000 (Overheating in new homes report by NHBC Foundation, 2012.). Although it’s undeniable that we need to address overheating and make sure all new homes are effectively designed for thermal comfort, we must stop placing the blame on insulation because it’s equally effective at keeping heat out as it is keeping it in.

Saying that overheating is the result of insulating and making homes airtight is too simplistic. What’s at play is a combination of poor volumetric and spatial design, technical detailing and specification and location.

Poor volumetric and spatial design

Moving away from the tall ceilings of Victorian housing in the UK and colonial properties in India and Australia, we have lowered the ceiling height of our homes to improve winter comfort. In doing this however, we have moved the stratified high heat zone into our occupied lower level comfort zone.

Previously, these stratified zones helped to keep the low-level comfort zone spaces cooler. Now, however, because of these lower ceilings, it’s now typically 1-2oC warmer in peak summer days in this comfort zone.

Yet at the same time as lowering our ceilings, buildings in the UK have also moved from large open plan rooms to a smaller cellular arrangement that complements how we now use spaces and to help with heating patterns in winter months.

But this arrangement can restrict cross ventilation strategies and mean some buildings rely on single sided ventilation. This is all well and good if the prevailing wind is consistently on the same side, but that’s not always the case.

In these situations, it can lead to poor ventilation and overheating. For instance, a typical apartment block design will have a central staircase or service shaft with two apartments on one side and two on the opposite. This results in the old ‘back to back’ arrangement of terraced housing and means that the apartments will have windows with only one aspect.

If you then add in issues with stagnating air over the summer months or the fact that many building occupants will open windows during the day letting pre-heated air into the space, levels of comfort become a real issue.

Technical detailing and specification

A lack of consideration around technical detail and specification is also a contributing factor to overheating in our buildings.

Despite the misconception that insulation is the cause of overheating, used effectively, it can actually help prevent excess temperatures. Insulation prevents solar gain/radiant transfer through the fabric of a building during summer months and retains heat energy in winter to keep us warm.

The problem that can occur with insulation causing overheating is where insulation is not specified and/or installed effectively.

For instance, in apartment blocks with communal heating and hot water, centralised service pipework is often located in stairwells or service zones, but is typically not insulated correctly. In these instances, heat from this pipework disperses into the service zones and then the apartments. This is a real issue because communal services and spaces can’t be controlled by the apartment occupants.

Another cause of overheating is a lack of understanding between thermal mass and thermal insulation. A lot of people think they are the same thing but they play very different roles in a building.

If insulation is placed to the underside of a concrete floor or roof soffit for example, then the mass of the concrete cannot be used as an absorber of excessive heat. Placing the insulation in this position effectively makes the building into an oven.

Fitting the insulation on top of these finishes however, can improve the efficiency of the mass to absorb heat and thereby reduces the risk of overheating. When used in conjunction with good cross ventilation strategies, this then makes the building perform like a traditional pantry used to keep produce cool in summer months.

Issues around thermal mass versus insulation are also problematic in the UK as, increasingly we’re using more lightweight construction materials like timber or metal frame, and aircrete blockwork. Many specifiers don’t always consider how the thermal mass will affect the building performance. Because lightweight materials don’t have the thermal mass, heat is not absorbed by the fabric to offset temperature gains through the day. Framed construction and aircrete blockwork can be used in highly effective building fabric specifications, but specifiers need to understand the building physics and specify the appropriate solutions to go alongside them.

Improper specification of glazing is another issue in the overheating of homes as properties can be designed without the right ratio of glazing to solid wall. Incorrectly applied solar coatings or too much glazing on south facing facades for example, can lead to excessive temperatures and overheating. To reduce this issue, the UK should take inspiration from the techniques used in the Middle East and Southern Mediterranean, for instance using Mashrabiya.

Location

A final contributing factor to the overheating of homes is location. Urbanisation means more homes are being built in cities where factors such as the urban heat island effect (where metropolitan areas are warmer than surrounding rural areas due to human activity) cause increased temperatures.

In cities, you also find that those living in low level dwellings have security concerns about leaving windows open at night or do not open windows because of noise. This means that heat inside the building is not purged at night, again, leading to potential overheating. A natural solution to this problem is, again, a technique used in Middle Eastern design where homes are built around enclosed courtyards. Alternatively, a background solution would be a mechanical ventilation system that continuously removes stale / hot air from the building and ensures fresher air is constantly available. Such systems must be used with a purge solution like night-cooling ventilation so spaces can be quickly cooled ready for the next day’s weather pattern.

As these examples illustrate, the reasons for the overheating of homes can be a lot more complex than simply an excess of insulation. To prevent overheating and create greater levels of thermal comfort, what’s needed is greater consideration of every aspect of a building fabric, including its design, specification and installation, and a more holistic approach to a home and its locality.