These findings came out of a national eight month study in over 500 homes. Sustainable Homes, who managed the study, assessed homes and behaviours of people living in their homes throughout England. Thirteen leading housing associations provided homes for the study.
This is the third article of the series on how people use energy in their home. It focuses on the effects that draughts have on the perception of wintertime comfort. Cold draughts can have detrimental effects on health and can be fatal for elderly occupants. Building regulations require that new homes are built to demanding insulation requirements using the Standard Assessment Procedure (SAP), and pressure-tested to demonstrate air-tightness – but even so, some new homes are still considered draughty by their occupants.
Figure 1: Reported draughtiness according to EPS banding
For existing homes, Energy Performance Certificates (EPCs) are required for all properties offered for sale or rent. EPCs use Reduced-data SAP (RdSAP) to calculate an energy rating, which, like SAP, uses a scale of 1 to 120, with 100 representing a zero-carbon home. However while the EPC survey is fairly extensive it also needs to be cost-effective, which means that it isn’t possible to measure everything. One of the most important factors that EPCs cannot take into account is the effect of draughts. Draughts are a major problem, and particularly so for the elderly. A draught wicks heat away from the body causing it to cool. Falling asleep in a draught is a significant hazard for the very young and the very old as it lowers resistance to infections.
There is also a perception issue. Moving air gives the impression of a room being cooler even though the actual room temperature may not be lowered much. A resident may turn up the heating to combat this – but this wastes heat in two ways: Firstly, the rate of heat loss from the building rises as temperature increases. Secondly, the draught replaces heated air with colder air, causing greater heat loss and higher bills.
It isn’t possible for RdSAP to accurately measure ill-fitting doors and windows, or draughts from floors and lofts., and so assumptions are therefore made about air changes per hour (ach) which are based on other building characteristics, including its age.
Figure 2: Perception of draughts with coolness/warmth of home (Click here to enlarge).
As a result of draughts residents in low-SAP homes behave differently to residents in high-SAP homes. Residents in hard-to heat homes will often spend cold winter evenings in one room and heat that as effectively as they can – keeping the door closed and drawing curtains. The rest of the dwelling is therefore likely to be cooler than the design temperature for much of the time. Many residents add clothes rather than keep the heating high. But in higher-SAP homes, residents do not need to take so many precautions to keep the home warm. There are fewer draughts, and so the living room door may be kept open more, enabling warmth to spread to the rest of the house. This means that it is closer to its design temperature, and it becomes less necessary to put on extra clothes. As a result, homes that have been retrofitted to make them warmer for the resident do not always result in large bill savings.
While Figure 1 does show much less draughtiness for higher-SAP homes, one might equally ask why any SAP 81-91 homes should be perceived as draughty. Newer homes built to airtightness standards ought to eliminate any perception of draughts.
In order to enable proper ventilation of open fires, and also to limit condensation, older homes were not built to be completely airtight. Wooden doors and windows expand and contract in dry and damp seasons, and so natural ventilation removes warm air and replaces it with cooler air that then requires reheating.
Figure 3: Perception of coolness, against measured energy use
Figures 2 and 3, taken together show the effects that draughts have on a home’s energy use. Tackling draughty homes is one of the single most effective ways of improving comfort, and cutting energy use. Nevertheless, doing so is not without problems, since reducing ventilation within the home can lead to other problems, such as excessive moisture and condensation and, in some cases, growth of black mould which can impact on the health of the residents. So ventilation needs to be controlled, rather than completely restricted.
We would like to thank Gentoo Group, Hastoe Housing Association, Home Group, Islington and Shoreditch Housing Association, Knightstone Housing Association, Leeds and Yorkshire Housing Association, Liverpool Mutual Homes for being part of this important national research.
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To read the full National Energy Study Two report, click here.
For Part 2 of this blog series, click here.