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In a changing climate there is increasing concern about the risk of overheating in UK buildings, particularly those with a low-carbon footprint which cannot rely on mechanical cooling. This gives rise to concern among building professionals about how overheating risk can best be assessed. Current Chartered Institution of Building Services Engineers (CIBSE) guidance uses a simple definition of overheating as the exceedance of 28°C for more than 1% of occupied hours, based on simulations using weather files from a 'design summer year' (DSY). There is increasing evidence that this criterion is both insensitive and open to abuse. This paper uses field surveys of thermal (dis)comfort and the adaptive thinking behind the British and European Standard BS EN15251 to propose a new approach. It takes account of the effect of indoor and outdoor climate on the dissatisfaction of building occupants. An alternative definition of overheating in buildings is proposed, along with an approach to predicting the magnitude and/or frequency of occurrence of overheating in buildings. Dans un climat en evolution, il existe une preoccupation croissante a l'egard du risque de surchauffe dans les immeubles du Royaume-Uni, en particulier ceux qui ont une empreinte carbone faible et ne peuvent pas compter sur un refroidissement mecanique. Cela amene les professionnels du batiment a se preoccuper de la maniere dont le risque de surchauffe peut etre le mieux evalue. Les informations actuellement fournies a titre indicatif par le CIBSE (Chartered Institution of Building Services Engineers) utilisent une definition simple de la surchauffe comme etant des temperatures depassant 28°C pendant plus de 1% des heures d'occupation, sur la base de simulations utilisant les fichiers meteorologiques de l'indice DSY (« Design Summer Year ») correspondant a une annee a ete chaud moyenne. Il est de plus en plus manifeste que ce critere n'a pas la sensibilite necessaire et incite aux abus. Cet article utilise des enquetes de terrain portant sur le confort ou l'inconfort thermique et les idees d'adaptation qui sous-tendent la norme britannique et europeenne BS EN15251 afin de proposer une approche nouvelle. Il prend en compte l'effet du climat interieur et exterieur sur l'inconfort des occupants de l'immeuble. Une autre definition de la surchauffe dans les immeubles est proposee, ainsi qu'une approche permettant de prevoir l'ampleur et/ou la frequence de l'apparition de cette surchauffe dans les immeubles. Mots cles: confort thermique adaptatif, confort, annee a ete chaud (DSY), inconfort, surchauffe, normes [ABSTRACT FROM AUTHOR]

Windows are central for the development of liveable nearly zero-energy homes and require careful consideration. Various studies have indicated that the effect of windows on energy consumption may change significantly with improved building insulation levels. Current guidelines on windows may therefore not apply in very well-insulated buildings, and more up-to-date information is needed about window solutions that are appropriate for the new conditions. This study maps the effect of multiple combinations of window size and basic glazing—and frame properties on energy, daylighting and thermal comfort in nearly zero-energy houses located in the European cities Rome and Copenhagen. The aim was to identify options that can support the easy and robust design of future homes with typical use of roof and façade windows. Hourly daylight levels were calculated in DAYSIM, while space heating demand and operative temperatures were calculated in EnergyPlus. The results support previous findings on the limited ability of nearly zero-energy buildings to utilise solar gains. It was found that U -values are becoming increasingly important for the energy performance of windows. The paper sketches the increased flexibility and related possibilities that may appear with improved roof window frame constructions and glazing U -values far lower than currently standard levels. [ABSTRACT FROM AUTHOR]