Can I calculate my own U values?

We would humbly suggest not as it is quite involved and requires specialist software. Insulation manufacturers will do U value calculations and some even offer an on-line facility. However remember that the manufacturers will only promote their products and may not always offer the best solution or value for money.

Fortunately we are highly experienced in this area and advise our customers in the area on a daily basis. To assist we have produced calculations and suggested products to achieve U values for a wide range of common constructions as per the list below.

If your construction is not covered in any of the illustrations then we can calculate the U value specifically for you. Send us the construction details by using the "Send Enquiry" form and we will contact you in return.

What is a U Value? (Unit W/m2k)

A U value is the rate of heat transfer per square metre of a structure i.e. the wall, roof or floor. The lower this figure is the better as this means there is less heat transfer. The U value is calculated by evaluating the insulation effect of the component parts of the building's structure. For example, calculating the U value of a traditional brick and block wall takes into account the effect of the bricks, cavity, insulation, blocks, plasterboard etc.

Do insulation products have U values?

No they don't but they make the most significant contribution to the overall U value of the structure.

What is thermal conductivity? (known commonly as "k value" of "lamda value" - unit W/mk)

Thermal conductivity is the rate at which materials transfer heat energy. Every material from insulation, wood, concrete etc has a thermal conductivity. It is a physical property of that material that is measured and given a value. The lower this value the better at insulating the material is because it transfers less heat. The figure is the same irrelevant of size or thickness.

What is thermal resistance? (known commonly as "R value" - unit m2k/W

Thermal resistance is a measure of the amount of resistance to heat transfer a material of a given thickness provides. Simply it is a measure of how much insulation is provided. It is calculated by dividing the thickness of the material by its thermal conductivity. Here is an example:

Fibreglass loft insulation has a k value of 0.044 W/mk.

So 100mm thick fibreglass has an R value of thickness (m)/thermal conductivity ie 0.100/0.044 = 2.27 W/m2k.

And 200mm thick fibreglass has an R value of thickness (m)/thermal conductivity ie 0.200/0.044 = 4.54 W/m2k.

So doubling the thickness doubles the thermal resistance or amount of insulation provided, which is common sense really. However doubling the thickness does not have a proportional effect on the U value!

When should U values be calculated?

Ideally U values should be calculated at the design stage of the building as they will determine what insulation products need to be used. However U values can be calculated at any stage during the project as long as all the information of the structure's make-up is available. The lower the U value, the thicker the insulation needed, so this ought to be accounted for when designing the structure of the building.

How do I know what U values to go for?

This depends on a number of factors from the type of building to the demands of the client and the issues that are important such as future heating costs or sustainability. Obviously we would advise  to insulate as much as is practical and go for a really low U value! However we are not alone and designers and builders increasingly recognise that the most important factors in designing sustainable structures and reducing carbon emissions is, to coin a phrase, insulation, insulation, insulation!

Here is a guide for the ranges of U values from the minimum usually required to the best that can reasonably be achieved.