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Insulation: does size matter?

At EWI Store, we carry a big range of insulation thicknesses, and we can get any thickness you need specially manufactured for you. We are going to ask the question: does size matter, and how thick can you go?

What thicknesses do you have in stock?

We carry both mineral wool and expanded polystyrene in stock, with the former going up to 120mm and the EPS topping out at 100mm as standard. We carry 90 and 100mm EPS in store as a standard product, and they are our most popular sizes. Why is this?

When carrying out a retrofit project, adding insulation to an existing 9 inch brick property, 90mm of EPS insulation will surpass the 0.3W/m u-value that needs to be achieved to meet building regulations. 110mm of Rockwool will achieve the same performance value.

New builds and exceeding regulations

If you have a new build project where you are using EPS to get a single skin wall up to the required u-value, then you will need more than 90mm. This is because new builds have a higher standard of insulation thickness required. This table gives an idea of the u-values you can achieve with graphite EPS on a 220mm brick wall:

Thickness U-Value
90mm 0.29
100mm 0.26
120mm 0.22
150mm 0.18
200mm 0.14
250mm 0.11

New build projects need to reach a wall u-value of 0.18, so we do often get asked to supply 150mm or similar insulation.

What thickness of Rockwool should be used in new builds?

If you want to achieve the same performance with Rockwool, we would recommend going for 200mm insulation. This thickness on Thermalite block or similar should give you a u-value of 0.18. As with all these calculations, make sure you get a u-value analysis tailored to your project before you order your materials, as you don’t want to be told you are a few mm off of being compliant once the job is done!

How much do these specially-cut insulation boards cost?

You may be surprised to know that the cost of cutting these extra thick boards is less than you would expect. Depending on the amount you are going to order, we can provide you with your EPS at a similar cost in terms of volume, compared to other stock sizes. If you would like a quote for a particular thickness of board, just give us a call and we will be happy to help.

Fixings for oversize boards

We also get asked for mechanical fixings for these large boards. For most oversized boards, we carry the appropriate fixings or can get them ordered. For extremely thick insulation over 200mm, you may need to recess your fixings into the insulation to ensure they are long enough to bite into the brick below. Ask us if you are not sure about the right fixings for your job.

Remember, if you’re not sure about anything, just call EWI Store and we can talk you through all of your requirements.


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