What is U-Value? And Why Does it Matter?

When you start looking at insulating materials, like loft insulation, you may quickly become confused with complicated technical terms. In this blog post, we will break down these terms and help you to understand the importance of how U-values will improve the sustainability and performance of your buildings. 

What is a U-Value?
A U-value is the measure of the overall rate of heat transfer in your building. The lower the U-value, the more efficient the construction is at keeping the heat flow through the structure. Whether you have converted a garage/loft or are looking around for insulation, you will have come across the term ‘U-Value’. Whilst the term U-value is rarely explained, it is regarded as an important area to find the right insulation, meet certain aspects of building regulation, and receive planning permissions to sort any project. 

The Lambda value measures the thermal resistance of the layers to make up an entire building element – this can include a roof, wall, or floor. Thermal transmittance, also known as U-value, is the rate of transfer of heat through a structure (which can be a single material or a composite), divided by the difference in temperature across that structure. The better the insulation is on a structure the lower the U-value will be. If the insulation is fitted poorly, with gaps and cold bridges, then the thermal transmittance can be considerably higher than desired. 

Why do U-values matter? 
The U-value is a number assigned to a section of your building to determine how effectively they prevent heat transmittance. The lower the U-value the better the insulation, meaning your house will stay warm in the winter and cool in the summer. Whether you are qualified or not, navigating through technical information can be a complex task. Below is a list of the basic requirements that you would need for new builds, extensions, and refurbishment. 

Residential New Builds  Wall FloorPitched Roof (Ceiling/Rafter)
England 0.280.220.16/0.18
Wales (Domestic in Character)0.210.180.15/0.15
Wales (Other)0.260.220.15/0.18
Scotland*0.250.200.15/0.15

*Refurbishment/extensions/conversions of unheated building 

Non-Residential New Builds Wall FloorPitched Roof (Ceiling/Rafter)
England0.220.180.14/0.14
Wales0.220.180.14/0.14
Scotland 0.18 0.150.14/0.14
Residential Extensions WallFloorPitched Roof (Ceiling/Rafter)
England0.280.220.16/0.18
Wales0.210.180.15/0.15
Scotland* 1. 0.17
2. 0.22
1. 0.15
2. 0.18
1. 0.11/0.15 
2. 0.13/0.18

*Value 1 is for when the existing walls and roof values are worse than 0.70 and the floors worse than 0.25, otherwise use value 2. 

Non-Residential Extensions Wall FloorPitched Roof (Ceiling/Rafter)
England0.280.220.16/0.18
Wales (Domestic in Character)0.210.180.15/0.15
Wales (Other)0.260.220.15/0.15
Scotland* 0.25 0.200.15/0.15

*Refurbishment/extensions/conversions of unheated building 

Residential Refurbishment WallFloorPitched Roof (Ceiling/Rafter)
England**0.30¹ /0.55²
0.25
0.16/0.18
Wales**0.30¹ /0.55²
0.25
0.16/0.18
Scotland* 1. 0.17
2. 0.22
1. 0.15
2. 0.18
1. 0.11/0.15
2. 0.13/0.18 

*Value 1 is for when the existing walls and roofs are worse than 0.70 and the floors worse than 0.25, otherwise use value 2. 

**¹Used for internal or external walls ²Used for cavity insulation

Non-Residential RefurbishmentWallFloorPitched Roof (Ceiling/Rafter)
England**0.30¹/0.55²
0.250.16/0.18
Wales** 0.30¹/0.55²
0.250.16/0.18
Scotland* 0.25 0.200.15/0.15

*Refurbishments/extensions/conversions of unheated buildings
**¹Used for internal or external wall insulation ²Used for cavity insulation 

Conversion of the heated building (Scotland Wall FloorPitched Roof (Ceiling/Rafter)
Residential 0.300.250.25/0.25
Non-residential 0.300.250.25/0.25

Achieving U-Values 
A great way to determine your U-value would be to consult a professional however another way would be to use a ‘U-value’ calculator. A leading manufacturer of insulation, Kingspan, are a great example of a great online tool which can get you to a value within a few minutes.  

Date Posted: 11th August 2022
 

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