What is a U-Value?

What is a U-Value?

A U-Value refers to a unit of measurement describing how much heat loss is involved in any type of building element such as a window, wall, floor or a roof. In basic terms, it measures how well particular parts of a building can transfer heat.

A low U-Value indicates the material is good for retaining heat, while if it loses heat then it means it has a high U-Value. When it comes to your home, a low U-Value is preferred.

Why U-Values?

When it comes to building regulations, U-Values are important because they are used during the construction process of a new building. The idea behind using U-Values is to keep carbon emissions low, reducing energy bills and ensuring that buildings produce a more comfortable living or working environment.

U-Values are assessed for their energy performance by the Government’s Standard Assessment Procedure (SAP) and maximum U-Values are set out during the design process of the building.

How U-Values are calculated

Depending on the thermal resistance of the building materials used, and the thickness of each layer, this forms the basis of the equation that enables the thermal conductivity of each layer to be calculated.

In scientific terms, the U-Value is measured as W/m2K, or watts per-metre-squared kelvin. In layman’s terms this means that the amount of energy in watts that travels through one square metre of material, for every 1 degree difference in temperature between the inside and the outside.

This can be applicable to a wide range of different materials and the typical U-Values of a single glazed window with a wooden or PVC-U frame are generally higher than those of a solid brick wall or a standard 30 degrees pitched roof. Insulating the house can reduce U-values by around two thirds, which is why many people decide to insulate their cavity walls or get their loft insulated.

What U-Values mean for your home extensions

Choosing double glazed windows or insulating roofs in your conservatory or home extension can lead to a lower U-Value. It is worth taking the time to explore which materials have a lower U-value so that you can reduce the amount of heat loss and overall heating costs of your home.