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What is U Value

The U-value measures how well a building component, e.g. a wall, roof or a window, keeps heat inside a building. For those living in a warm climate the U-value is also relevant as it is an indicator of how long the inside of the building can be kept cold.

Comfortable indoor climate with good U-values

In both cold and warm climates good U-values are important measures for understanding the amount of energy that is needed to keep a comfortable inside temperature. Learn more about why u-values matter.

What is the U-value?

The U-value is a measure of the heat flow through a building element as illustrated in the figures to the right. The higher the U-value the more heat flows through so a good U-value is a low one as you want to keep heat inside the building or outside depending on the climate you live in. Find out why U values are important.

The technical explanation of the U-value

Getting a little technical the U-value physically describes how much thermal energy in Watts [W] is transported through a building component with the size of 1 square meter [m²] at a temperature difference of 1 Kelvin [K] (=1ºC). Thus the unit for U-values is W/(m²K).

So what is a good U-value? For external walls, roofs, etc. a U-value of less than 0.2 W/(m²K) can be called good. This value can be reached by using thermal insulation with a thickness of about 20 cm or more. For windows the U-value should be less than 1.0 W/(m²K).


What is SAP?

SAP is the government's approved methodology for calculating the energy performance of buildings. It is used to demonstrate compliance with Building Regulations Part L requirements and to produce Energy Performance Certificates for new buildings.

The score is based on factors such as insulation, air tightness, heating systems, ventilation and lighting. Renewable technologies such as solar power are also taken into account.

How can I submit my drawings?

You can submit your drawings by email to raymond@brsuk.co.uk. We'll shortly be implementing an online submission service where you'll be able to login on our website and upload drawings directly...watch this space!

To contact us about SAP Calculations and U Values: