'U' values for external non-fire and fire rated doors are listed within Building Regulations and dhf member companies offer CE marked insulated products that are U value rated.
The thermal insulation value of a door is expressed as a 'U'= W(m2)K. The value should only apply to the entire door, not the individual panel section or insulated lath, as detailed in BS EN 12428-2000.
The intended usage of the door should be evaluated before the decision on its ideal U value is taken. For example, it is not necessary for a warehouse door that is in constant use to be highly insulated if it spends most of the time in the open position. It is better to specify a rapid action door with low insulation in this circumstance.
If the building under construction must achieve a U value of 0.7 or better it does not necessarily follow that the door or shutter should meet this U value. Uninsulated products, or products with a lower U value, can be used as long as compensations are made elsewhere in the building design. It is the building itself that must meet overall energy efficiency standards, and the installation of insulated doors is just one of many ways of helping to achieve this.
The U value of a doorset can vary dramatically dependant on its design, as well as how much area is glazed. Generally, the more glazed area the higher the U value. A high U value means a poor thermal performance. But specifying performance glass units can improve the U value. Some glass units can perform as well as an unglazed door slab.
The U value declared in a Declaration of Performance (DoP) must be verified by a notified body.
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