Buildings Guide

Building Envelope  »  Fenestration


Windows are the least insulating element of the building shell. At the same time, they represent an important part of the building envelope. Windows let in daylight and admit passive solar heat to the internal spaces or indeed, lose heat to the outside. Larger windows allow increased amounts of daylight in to the space albeit at the cost of unwanted heat transfer. There is an optimum design for windows, which attempts to provide a balance between these energy flows. This balance is based on the orientation, location, obstructions and user requirements. Generally, between 25% and 45% glazing ratios are regarded as being the optimum. This means that no more than between 25 and 45% of the total facade area of a building should be glazed. Double or triple layered glazing systems with low e coatings offer cooling or heating energy savings in the range of 3 % to 10% compared to typical single glazing systems.

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