The application of air layers in building envelopes: A review

Air layer involved envelopes (ALIEs) have gained considerable popularity in modern building design and construction, owing to their great potential in improving the building thermal performance. Basically, the air layer functions as an extra insulation layer or as a ventilation channel. This paper presents a literature review on building envelopes that contain inner air layers by tracing recent studies on existing air layer involved applications and technologies in walls, windows, roofs. The structural characteristics, the driving forces, the effects of the inner air layers, and the benefits of different types of ALIE systems are summarized and classified. And then operation modes of air layer used in building envelopes are roughly classified into three types: the enclosed type, the naturally ventilated type and the mechanically ventilated type. At the end, this paper analyzes current research gaps and provides possible future research directions on air layer technologies in building envelopes.