The influence of lightweight aggregate concrete element chimneys on the airtightness of wood-frame houses

Energy efficient buildings must be constructed as airtight as possible. In Norway the airtightness requirements have become stricter. This leads to a growing interest for airtight constructions and methods. Element chimneys of lightweight aggregate concrete, LWAC, are widely used in Norway. Air leakages are frequently observed in connection with these chimneys. The leaks are found either through the element, as a result of insufficient surface treatment of the air permeable element, or through the joint with the roof. This article discusses the influence that LWAC element chimneys can have on the airtightness of wood-frame houses. This is done by measurements and calculations. The influence of the sealing method used in the joint with the roof and the influence of the surface treatment of the LWAC elements on the airtightness is investigated. The results show that even the simplest sealing in the joint with the roof is adequate because of the limited circumference of the LWAC chimney. The results also show that the airtightness provided by the surface treatment of the chimney is very sensitive to the workmanship. If the workmanship is thorough, the influence of a LWAC element chimney on the airtightness of a wood-frame house should be negligible.