Your Ultimate Guide to U-Values

Insulation is crucial to the health and comfort of any property during seasonal change. Whether you settle on blanket insulation or favour a multifoil, you need to be aware of…


Insulation is crucial to the health and comfort of any property during seasonal change. Whether you settle on blanket insulation or favour a multifoil, you need to be aware of the benefits and drawbacks of your chosen material. A straightforward way to assess the performance of any material is by learning their ‘U-Value’. Should you have spent any time looking into insulation, you’ll be familiar with the term. However, perhaps you’re still unsure as to what it means.

There’s no need to worry! At SuperFoil, we’ve compiled your ultimate guide to U-Values. Learn everything you’ll need to know when selecting insulation for your home here.

What Is A U-Value?

A U-value is a number that represents the total thermal resistance of layers in a building element – so a wall, a roof, or a floor. It also takes into account any air gaps or fixings. To put it as simply as possible, the lower your U-value, the better insulated your building element is. Materials with higher U-values are less efficient, and if used, your property will require additional insulation.

Any U-Value is presented in W/m² K. W/m² K stands for Watts (the rate of heat flow) through 1m² of a structure when temperature through the structure rises by 1 degree (K or ˚C).

How Do I Calculate U-Value?

Before you can take extra steps to insulate your home, you need to know the U-Value of your roof, your floors, and your walls. You can calculate these values for yourself, but there are a few steps you need to take before the equation. To calculate U-values, you need to understand thermal conductivity, thermal resistance and thermal transmittance.

Thermal Conductivity

Thermal conductivity, or Lambda, represents the rate heat passes through a material. Conductivity is measured in watts per square metre of surface area for a temperature gradient of one celsius for every metre of thickness. The lower the conductivity, the more efficient your material at retaining heat.

Here are some average thermal conductivity values of popular construction materials to guide you!

  • Bricks – 0.84 W/mK
  • Glass – 1.05 W/mK
  • Timber – 0.14 W/mK
  • Aerated slab concrete – 0.16 W/mK
  • Lightweight concrete – 0.38 W/mK
  • Dense concrete – 1.40 W/mK
  • Gypsum plaster – 0.46 W/mK
  • Concrete roof tiles – 1.10 W/mK
  • Clady roof tiles – 0.85 W/mK

Thermal Resistance

Thermal resistance, or the R-Value, is the ability of a material to interrupt the flow of heat. It’s the thickness in metres of the element divided by its conductivity. Resistance is expressed in m2K/W. The higher the value, the better your component performs.

If your material includes multiple components, the overall resistance of your material is all individual elements combined.

Thermal Transmittance

Thermal transmittance is another term for U-Value, and it measures the rate of heat loss in a building component. Any U-Value considers all elements in a property, such as air gaps, surfaces and any thermal bridges.

To calculate the thermal transmittance (U-Value, add all your R-Values (thermal resistances) together and finish with a simple calculation. Divide the number 1 by the total of your R-Values, and you’ve got your U-Value. Lower is better.

Why Do U-Values Matter?

When your building is constructed with materials that aren’t thermally efficient and retentive, you’ll lose a lot of the heat you’re generating. In short, with high U-Values, you’ll be spending more money than necessary trying to keep your home warm! Calculating your U-Values is an excellent place to start to determine how much extra insulation you should purchase.

You can request a U-Value insulation calc for any project at SuperFoil if you don’t feel confident completing equations alone. We can advise clever insulation solutions for your home and provide plans to reduce your energy bills.


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