What You Should Know about U Values

Bi fold doors come with U values. These gauge the energy efficiency of the units and are managed by UK building regulations which have become more strict over the years. The higher the U value, the better the performance of the individual product.

A U value, however, is more than a label or product specification. There is a strong mathematical aspect to it. In fact, the trait itself is a formula measuring heat transmission rates through specific materials. It is measured as Watts per metre squared, or W/m2.

The components of the equation include the heat lost in watts, per square metre; the lower this number, the better. Optimal numbers vary depending on whether a house is older or being built new. Different regulations must be met if the project is an extension to an older home, is new, or replacing an existing frame.

Examples include the L1A New Dwelling specification, requiring 2.0 W/m2K, and L1B Existing Dwelling – 1.8 W/m2K.


How to Measure U Values

There are three primary types of measurements here. One is thermal transmittance of the door’s glazing (Ug). Others include the frame’s thermal transmittance (Uf) and transmittance of the entire window (Uw). The spacer/edge effect of the complete unit is also factored in, and is called the PSI value. All these factors must be considered and not just a single U value stated by many bi fold door suppliers.


Door Characteristics Impacting U Value

The energy rating of a bi fold door is directly affected by its size. Also, the number of panels and how the complete unit opens have an impact on the U value while systems that open inward or outward can have completely different numbers. It is therefore important to consider all these when looking at actual efficiency.

When shopping around, look at each company’s range of products and the different levels of product variation and U value. These tips are intended to provide insight into understanding what U value means in terms of bi fold doors and their glass.