Timber is increasingly used in construction of buildings due to its green credentials and ability to reduce the overall construction period when compared with conventional materials. However, the lack of thermal mass along with the low U-values can be a risk factor in increasing overheating. This paper investigates the indoor thermal conditions and overheating risk in prefabricated timber buildings focusing on two buildings built in the last decade in the UK, Oxley Woods and Bridport. The study employs a combination of different methods: postoccupancy evaluation, thermal comfort surveys, monitoring and simulation. The results reveal high satisfaction rates in both buildings, with lower thermal sensation in Oxley Woods where monitored internal temperatures were higher, demonstrating higher adaptive capacity due to the increased use of controls. Overheating analysis through the use of the CIBSE comfort model revealed extreme summertime overheating in 67% of the spaces during the monitoring periods, while for the simulations in just 22% of the spaces. With the adaptive thermal comfort model (BSEN15251) overheating is more frequent at Oxley Woods with cold discomfort also becoming an issue in both buildings. Comparison of the two comfort models suggests that the CIBSE model is more sensitive predicting extreme occurrence of overheating, while the adaptive BSEN15251 model is closer to the results of the thermal comfort evaluations, with availability of controls enhancing adaptation further. Comparing the findings with those from previous studies, which were mostly built with heavyweight materials, indicate that high temperatures were more frequent in the current study, highlighting that the lack of thermal mass in prefabricated timber developments increases the overheating risk, even in mild summer weather conditions as occurring in the UK.

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Colonial Revival style residences have unique architectural features amongst others. They are common multi-family residences in the United States with no or limited information about their performance. The research purpose is to assess indoor comfort, energy performance, and thermal indices in multi-family Colonial Revival style residences. The research questions include (i) Do Colonial Revival style buildings perform better than other old buildings? (ii) Do the buildings consume additional electricity than typical and other old buildings? The research examined four case studies in Hartford County, Connecticut. The investigation explored comfort surveys, monitoring, collection of actual electricity usage, and assessed thermal indices using mathematical models. The average indoor temperature of 25.4 °C and relative humidity (RH) of 61.3% are reported. About 67% of the residents are thermally comfortable. The research noted significance between thermal sensation and other variables, excluding how occupants feel about the air movement. The average number of hours of temperature exceeds 28.0 °C and 30.0 °C marks for over 11.4% and 2.5% of the time, respectively, except in one of the buildings. The mean indoor temperatures are within the applicable bands of the adaptive comfort models. The averages of actual thermal sensation vote (TSV) ranged from 3.32 to 4.37 on a 7-point sensation scale. The mean neutral temperatures varied from 24.2–25.6 °C. The average monthly electricity bill is within the national average for residences in summer, excluding in August. The mean wet-bulb globe temperature (WBGT) of 21.1–22.3 °C and summer simmer index (SSI) of 30.1–32.4 °C are calculated as feasible bands for thermal indices in the buildings. The basements are more comfortable than other spaces within the case studies. The research outcomes can be used for future developments of Colonial Revival style and other similar buildings. The study recommends interventions such as retrofit to improve the performance of some existing Colonial Revival style buildings, especially the older ones that are less insulated with outdated equipment and appliances.

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