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Janex windows used in Bath University's HemPod experimental building

There are two factors involved in the thermal efficiency of windows and doors: the integrity of the products themselves, and the integrity of the installation. Janex’s unique service package means we take full responsibility for installation standards as well as for the design and manufacture of our windows and doors. Janex windows were chosen for Bath University’s HemPod experimental building. In air-tightness tests carried out by Building Analysis and Testing Ltd, they contributed to an air-tightness that comfortably met Passive House standards. Air Change was measured at 0.55 m3/hr.m3 Building Volume, compared with the Passive House requirement of less than 0.6 m3/hr.m3.

“Generally, the openings in an envelope are the greatest weaknesses, so thermal efficiency through good design of door and window surrounds, and the use of double or triple glazing, such as in the Janex system, can make a considerable difference to the thermal performance of a building.

Wherever thermal bridges occur, the thermal efficiency is reduced. Typically these occur through metal connections and lintels in walls, and poor design of door and window surrounds. Careful design, such as used in Janex windows and doors, reduces the incidence of thermal bridging. In conjunction with the monolithic construction of Tradical® Hemcrete, it was possible to achieve an envelope with minimal evidence of thermal bridging.

Significant quantities of heat can be lost through air-leakage. Although this can occur to a small extent through the floor, walls and ceilings, the majority is lost through the junction between opening elements and walls or through joins in the elements. We managed quite easily to achieve exceptional air-tightness in the HemPod by careful installation of the Janex door and windows, and found no evidence of air-leakage between the glazing and the timber in the units.”

Dr Mike Lawrence

BRE Centre for Innovative Construction
Materials Department of Architecture & Civil Engineering University of Bath