building regulations and U-values, EWI, external wall insulation and U values

Our insulated render systems are a great way to help improve the thermal comfort of your property. They are also a great way to reduce energy bills – less heat escaping through the walls means your boiler needs to work less hard. 90mm of our graphite enhanced expanded polystyrene (or EPS as it is more commonly known) can halve the heating part of your energy bill. Couple this with the fact that many older solid wall properties are also damp, wrapping your home in a watertight insulated render system can significantly improve the internal environment – providing a drier more comfortable dwelling.

Part L of Building Regulations stipulated though that certain targets have to be met when improving existing building fabrics (like walls) or when you are building a new property from scratch. The target for insulation is known as the u-value, and basically this shows heat loss for a given wall.

Insulated Render and U-Value Regulations

In the domestic sector, there are 3 targets that people need to be aware of

  1. Installing insulated render systems on existing properties;
  2. Installing insulated render systems on extensions on existing properties;
  3. Installing insulated render systems on new builds.

If you are adding insulation to existing properties (i.e. Target 1 and Target 2), you are only required to hit the targets if you are installing the insulated render system on more than 25% of the entire surface of the property.

This means that if you are trying to improve just a small part of the house such as the walls of an exposed cold bedroom, then potentially (provided this is less than 25% of the total wall area) you can add as little insulation as you want.

Now, without going too much into the maths behind the u-value target – every building fabric has an existing u-value, or a level of heat loss. If you add insulation to the building fabric, then there is less heat loss, so the u-value goes down. The targets set by the Building control can be used on every type of wall, it just basically means that the starting u-value will be different, and therefore the amount of insulation that is required to hit the target will vary.

To keep things simple, we are going to be concentrating on solid brick walls – which is a very typical building construction in the UK, and since they can’t be insulated with cavity wall insulation – a common building type that gets fitted with our insulated render systems.

An existing 225mm solid wall has a starting u-value of 2.16 W/m2k.

  • When installing render systems on existing properties, the target u-value that needs to be reached is 0.30 W/m2
  • When installing render systems on extensions on existing properties, the target u-value that needs to be reached is 0.28 W/m2
  • When installing render systems on new builds, the target u-value that needs to be reached is 0.18 W/m2

Insulated Render and Insulation Thickness

So what kind of thickness of insulation will achieve this? Well it varies whether you are using mineral wool or EPS.

  • To hit a u-value of 0.30, you require 90mm of EPS or 110mm of mineral wool
  • To hit a u-value of 0.28, you require 100mm of EPS or 120mm of mineral wool
  • To hit a u-value of 0.18, you require 190mm of EPS or 210mm of mineral wool

Obviously, it is worth pointing out that there is nothing stopping you beating the targets! If you want to add 300mm of insulation to your extension and take the u-value down to 0.12W/m2k, then there is nothing stopping you do it! At EWI Store, we can source EPS at any thickness between 20mm and 400mm!

So there you have it, the targets that need to be hit, and also the insulation thickness that is required to hit them.