Building a property can be stressful at the best of times, especially if you’re not completely up to date with the latest set of building regulations. To save you time and effort, our team has collected all the information you need to comply with new build cavity wall insulation regulations.
Note. We haven’t stopped there. We have also run the numbers and broke down the calculations so you will have all the tools required to ensure your new build is compliant.
Before diving into the regulations concerning cavity wall insulation on new builds, you probably should familiarise yourself with the ‘U’ value. Also known as thermal transmittance. The U-value measures the rate of health loss of a fabric. This may be your walls, roof, floors or even windows. Each fabric has its own U-value or rate at which it transmits thermal heat.
The equation for this calculation looks like this: –
Where ‘R’ represents represents thermal resistance of an element (internal wall OR cavity wall insulation etc ).
You may be wondering, what relevance does this ‘U-value’ have? Put shortly, it’s a number that buidling regulations use to check that your cavity walls are compliant.
The important thing to note is that a lower U-value it preferable from an insulation perspective. For example, metals typically have a high U-value and are good conductors of heat. Hence why your frying pan has a copper base. On the flip side a well-insulated wall should have a U-value of approximately 0.25.
Now that you’ve established the U-value, why not dive a little deeper into the regulations? Building regulations set out a reference U-value for external walls which property developers must meet. What is the target setting?
In simple terms, the U-value of your external walls should be less than 0.30 (L1A 2013). If the U-value of your new dwelling is above 0.30, then your home will not comply to buiding regulations.
The Department for levelling Up, housing and communities (DLUHC) announcement – As of June 2022 new build homes in England must cut an additional 30% in carbon emissions.
Although this statement is not directly aimed at cavity wall insulation, its important to understand its significance. As its compulsory to meet this target set by the DLUHC, one of the ways in which we can meet this is to minimise the amount of heat lost to your cavity walls.
You’re probably thinking – if I have already met the requirements on the maximum U-value required on the external walls, what else can I do?
Well, with the correct choice of insulation and building material its possible to achieve a lower U-value. It might come as a surprise to you, but this isn’t as difficult as it seems. In fact, a break down of the calculations which will ensure your external walls exceed the limits set out in building regulations has been made by us (just for you!!).
Let’s look at your typical external wall. It’s made up of multiple layers. Working from the inside out, the first layer is gypsum skim. This followed by your inner leaf then cavity wall insulation. With the final layer being the external wall.
In this example, you can pretend ther’s 4 layers. Each layer has its own thermal resistance, thus having its own independent U-value. However, to calculate the U-value of the external wall we must calculate the 4 layers as one item. Hopefully the equation mentioned earlier in this post will make a little more sense now. Lets brake it down.
Thermal resistance of gypsum skim, R1 = 0.17
Thermal resistance of internal leaf, R2 = 0.44 (4-inch face brick)
Thermal resistance of cavity wall insulation, R3 = 6.81 (Xtratherm PIR Insulation 150mm)
Thermal resistance of external leaf, R4 = 0.44 (4-inch face brick)
Note
Thermal resistance = Thickness / Thermal Conductivity
Xtratherm PIR thickness = 150mm or 0.15m
Xtratherm PIR thermal conductivity = 0.022
Hence, Xtratherm PIR thermal resistance, R4= 6.81
Plug the numbers into your calculator, and you should return a U-Value. The resuting U-value from our calculations…
What will you conclude here? Perhaps that hitting the maximum U-value (0.3) requirement in building regulation is easy enough to achieve. (Correct answer). In addition to this, with the correct choice of insulation you absolutely can surpass this figure. Which in turn contributes to the additional 30% cut needed in carbon emissions produced by new builds.
Its highly likely if you’re building a property that you would have opted for the cavity batt approach. However, there are circumstances where injected cavity wall insulation is required. The question remains, is this still complaint with new build regulations?
Since we advise against mineral wool, rockwool and foam insulation, In our example, we’re going use EPS carbon beads. Why? They offer excellent thermal properties with minimum risk. Why not assume that the cavity width is 100mm?
All you need to do is apply the same equation as the last example. However the thermal resitance of the carbon bead will differ from Xtratherm PIR.
Thermal resistance of gypsum skim, R1 = 0.17
Thermal resistance of internal leaf, R2 = 0.44 (4 inch face brick)
Thermal resistance of cavity wall insulation, R3 = 3.31 ( Xtratherm PIR Insulation 150mm)
Thermal resistance of external leaf, R4 = 0.44 (4 inch face brick)
Note
Thermal resistance = Thickness / Thermal Conductivity
Carbon Bead thickness = 100mm or 0.1m
Carbon Bead thermal conductivity = 0.033
Hence, Carbon bead thermal resistance = 3.03
Pluging this into your calculator should give you a value of 0.229, which is less than 0.3. Again, in this example you’re compliant with building regulations.
Hopefully, following our set of calculations you now have the tools to calculate what insulation material you need to meet building regulations. It’s important to note that different building materials will have different thermal resistances. Ultimately, this will effect your final U-value for the external wall.
Become an expert on cavity wall insulation in just 5 minutes! You can read more about the best insulation materials for your home right here in our Cavity Wall insulation Ultimate Guide.
We help families around the UK to live in an energy efficient homes through the use of insulation and installing eco-friendly boilers. We provide boiler grants as well as cavity wall insulation & extraction.
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