What is a U-Value?
A U-Value is a measurement of heat loss from the fabric of a building. Each element of a building is assigned a U-value which is a calculation based on that materials ability to transfer heat.
The lower the assigned U-Value the better that material is able to resist the passage of heat energy. This is why we assign U-values to our properties. This value allows us to design efficiently and with an eye on future heat loss.
How do I read the U-Value?
A U-Value is expressed a W/m2K. That is, as a Watt per metre squared Kelvin. More commonly you would hear it expressed as a U-value of 0.21. The figure of 0.21 is expressing the amount of heat loss from a metre squared of the nominated material in Kelvin. The lower this figure is the less heat is lost.
Most walls can be insulated to figures as low as 0.15 and in some passive house designs even lower than that. Building control regulations are changing so quickly in this area that is imperative that you talk to your SAP expert or to building control to get an up to date list of materials and their U-Values. This will help when you are choosing a construction method.
While brick and block methods are struggling to catch up with the building regulations the timber frame industry is well ahead in terms of the high levels of insulation values it can achieve. It is relatively easy to achieve a good U-value from using timber frame.
Remember with a U-Value the lower you go the more you save.
Ed Gordon is a Timber Frame specialist with a keen interest in Energy Efficiency and reducing the construction Carbon Footprint.
For more information go to http://www.gts-timber-frame.com
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