History lessons

Older buildings tend to be seen as a particular problem in the face of global climate mitigation targets and the drive to reduce ­energy use – and bills. Generally, heating and lighting have been the main consumers of energy in buildings, although with the rise in summer temperatures it is predicted that air-conditioning will soon surpass them. 

This general concern took practical shape during my study of the Georgian grade I listed Architectural Association (AA) School in Bedford Square, London, which had a low SAP rating and an issue with occupant comfort. In this case summer overheating was a particular issue, and occupants often asked about installing air-conditioning. My study took an experimental approach, and showed that traditional passive methods could save energy, lowering the carbon footprint while improving occupant comfort. 

The current focus is on retrofitting existing buildings to make them more energy efficient, or adding services to meet heating or cooling demands. For traditional buildings, especially listed ones, the need to preserve their character often conflicts with retrofit solutions, and the need to maintain breathability requires careful thought; meeting increased comfort demands often results in high energy use. Installing air-conditioning throws up issues that would seriously compromise building and may still not provide enough comfort; one modern air-conditioned extension at the AA achieved exactly the same level of occupant satisfaction as the traditional buildings while using a lot more energy. 

Sustainable architecture is too focused on technology-driven processes. We must remember that people, not buildings, use energy, and they have historically used traditional buildings more efficiently. My research adopted a retrospective lens: old buildings, after all, may have existed for centuries and been through much extreme weather. Just as people changed clothes to adapt to changing seasons, they also used additional layers such as tapestries, external awnings and blinds to adapt their buildings to the weather, with no additional energy expenditure. 

My research mainly used the experimental method to understand existing conditions and to test proposals. Based on historical evidence, various traditional controls were chosen and their efficacy for winter and summer tested in two near-identical rooms at the AA. One was designated the experiment room, which received treatments, and the other the control room, which remained unchanged. The winter experiment was carried out in March, and the summer one in July/August. Each ran for at least three weeks, with monitoring of existing conditions in week one, after intervention in week two, and post-experiment conditions in week three. After this occupants chose whether they wanted to continue with any of the installations.

Winter

The winter interventions were tapestries/wall hangings, local radiant heat sources such as foot and seat warmers and small personal radiators, task lighting coupled with natural daylight instead of ceiling lights, translucent curtains for glare control and warmer upholstery. Radiators were turned off during the experiment week. 

The internal room temperature in the experiment room was only slightly below that of the control room in the experiment week, and both rooms retained an internal temperature of well above 21°C, indicating that the building’s thermal mass was effective. Experiment room occupants reported that they were comfortable although there were individual differences. Local radiant sources were used only for an hour or two in the day, except for one occupant who benefited from the seat warmer. The occupant who benefited from wall hangings felt comfortable throughout, and did not use her radiator at all, even though she had reported feeling the coldest before the experiment. She initially found it difficult to believe the wall hangings could be a reason for this, until presented with the experiment results. 

The task lighting meant that ceiling lights stayed off until the blinds were drawn to reduce glare. The occupants initially disliked the translucent curtain blinds for aesthetic reasons, and reported them as a failure. However, time-lapse photography showed that all three blinds were drawn only on days when direct sunlight was streaming through the windows. On partly cloudy days, the middle blind with the translucent curtain was the only one that stayed up. The curtains were useful in blocking glare, but the effect was not immediately noticeable to the occupants. 

The heating had stayed off for the entire week after the experiment as well. Interest in using the treatments was initially low, but after their benefits were explained, most people were willing to try them. Even after their use participants were convinced the effects must be due to better weather rather than the interventions. As experiment results were shown to them, they quickly became enthusiastic participants.

 

Summer

Pre-experiment monitoring occurred during the hottest week of the summer, and temperatures exceeded 30°C internally. Thermal imaging showed internal blinds absorbing sunlight and giving off heat almost like radiators. The summer controls adopted were external awnings/blinds, opening up a chimney to facilitate stack effect cross ventilation within the experiment room, a ceiling fan (not strictly traditional in the UK but used in many hot countries) as well as night cooling. Task lighting and translucent curtains were tried again to check their efficacy for summer conditions.  

Perhaps unsurprisingly night cooling was the most successful option: just one window left slightly open, combined with chimney ventilation, produced a reduction in air temperature of up to  1.5°C. The awnings reduced the solar radiation gain. The chimney introduced a welcome draught, and the ceiling fan was used only on some days as on occasion it made the occupants feel too cold. The translucent curtains were very popular and different occupants tried them for their windows and were happy with the results. A follow-up study a year later saw some of the tested methods in place. The black blinds have now been replaced with light reflective blinds, the chimney was open for ventilation and ceiling fans were in the process of being installed. 

Many of the measures proposed can be adapted to current uses and can be used with modern services. They could be equally applicable to modern buildings. External awnings and shades, for example, have been the hallmark of many sustainable modern buildings. Passivhaus designs, for example, include strategies such as external shading, stack ventilation and night flushing. 

For the past few decades we have been using our traditional buildings in a way that goes against their grain – by not understanding how they were designed to work, and slowly denuding them of their components. This research shows that our approach to sustainability of traditional buildings needs to be rethought, and a return to a seasonal way of living could be a way forward. It is, perhaps, time for the flow of beneficial inspirations to reverse. We need to learn from the past, so that we may better design the architecture of today and tomorrow.

The proposed measures are low impact solutions, which put control back in the hands of a building’s users. These solutions serve to enhance, rather than compromise, the historic character of listed buildings. They could point the way towards a more sensitive, contextually relevant zero-carbon approach for historic buildings. 

Winter measures
Tapestries and wall hangings
Foot and seat warmers
Mini radiators
Task lighting
Translucent curtains
Warm upholstery

Summer measures
Blinds
Task lighting
Translucent curtains
Ceiling fan
Night cooling: chimney plus window ventilation

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Sarah Khan is a conservation architect and partner at Roger Mears Architects.