It is well known that living walls can reduce air conditioning demands on buildings during hot sunny weather, but little is known about their effectiveness at insulating buildings during cold weather. In this study we investigated the insulating effectiveness of a coating of English ivy Hedera helix covering the North wall of a solid brick-walled building in Manchester, U.K. in late winter 2012. Internal and external wall temperatures were monitored over a 36 day period on both bare and ivy-covered areas of the wall, along with the local ambient temperature. It was shown that the ivy covering increased the mean external wall temperature by 0.5 C and reduced temperature fluctuations; ivy covered walls were on average 1.4 C warmer at night but 1.7 C cooler in the middle of the day. As a consequence, calculated energy losses were reduced by 8%. The covering was more effective on cold days, but at temperatures above 12.2 C the ivy covering increased energy loss, because it shaded the outside of the wall from warming by short wave radiation. The results suggest that evergreen living walls can reduce heating costs, particularly when placed on the North of buildings, whereas on the South side deciduous climbers might be more effective.