I am becoming an insulation bore.

Friends, I am obsessed with the insulation I am about to apply to the outside of my house (link).

The installation is still 4 weeks away but I am thinking about it all the time. And if there is a lull in the conversation I may well introduce the topic a propos of anything at all:

Person A: “So I said to Doreen this relationship just isn’t working…


Me: “That’s very difficult. But have you thought about External Wall Insulation?

However,  aside from the risk of boring everyone I know, I have had two major concerns.

  • The first and more basic concern is about the flammability of the insulation.
  • And the second and more technical concern is whether or not the insulation will work as well as it claims.

I have now looked at both these issues experimentally. I’ll cover the measurement of the thermal conductivity in the next article, but here I take a look at the flammability of external wall insulation.


When I tell people about the external wall insulation (EWI) project I can see people internally say “Oh. You mean like Grenfell?” and then say nothing.

That appalling tale of misunderstood specifications that ended up with people putting flammable insulation on the outside of high-rise flats led me to believe that I need to personally reassure myself before going ahead. It would be unwise to take anyone’s word for it.

The insulation that will be applied to the outside of the house is called Kingspan K5, .

  • It is a thermoset foam which means that is manufactured and hardened by heating and so should not melt when heated.
  • This is in contrast with expanded polystyrene (EPS) foam which is a thermoplastic which will soften or melt on heating.

The K5 datasheet (link) contains detailed specifications of the performance in flame tests. For example:

“…achieves European Classification (Euroclass) C-s1,d0 when classified to EN 13501-1: 2018 (Fire classification of construction products and building elements. Classification using data from reaction to fire tests).

Extract from Kingspan K5 data sheet. Click for larger version

But what does this mean? I found this explanatory page and table.

Click for larger image

  • The C is a categorisation from A (Non-combustible) to F (highly flammable) and means “Combustible – with limited contribution to fire”
  • The s1 means “a little or no smoke” on a scale of s1 to s3 (“substantial smoke”).
  • The d0 means “no flaming droplets or particles” on a scale of d0 to d2 (“Quite a lot”)

This was quite reassuring, but the terms are rather inexact and I didn’t really know what it all meant in practice.

So I went down to the EWI Store, bought some K5 and did my own flammability tests.

Flammability test

My flammability test consisted of propping up a sheet of K5 and directing a blow torch onto its surface from a few centimetres away and then leaving it for 10 minutes.

I think this is a pretty tough test and I was pleasantly surprised by how the insulation performed.

The results are captured in the exceedingly dull video at the end of the page and there are post-mortem photographs of the insulation below.

The insulation remained broadly in tact and damage was limited to a few centimetres around the region where the flame reached the insulation. The rear side of the insulation did not appear to have been damaged at all.

After having performed this test I realised that I had forgotten to measure the temperature on the rear face of the K5. Doh!

So I few days later I repeated the test and measured the temperature on the back of the 50 mm thick insulation panel as the temperature in the interior of the insulation reached approximately 1000 °C.

Remarkably, after 10 minutes the rear had only reached 57 °C.

Overall these results are  better than I expected, and from a safety perspective, I feel happy having Kingspan K5 on the outside of my house.

Expanded Polystyrene Foam (EPS)

I also did flammability tests on EPS. But these tests did not take long – EPS lasts just a few seconds before burning and melting.

However, even for a material as flammable as EPS, in this external application, the risk would be very low. The foam would sandwiched between non-flammable external render, and a non-flammable brick wall.

You can read about the factors which mitigate the risk in this application at the following links

But I am still happy to be paying extra for the superior fire resistance of Kingspan K5.

But will the K5 really be as good an insulator as its manufacturers claim? I’ll cover this in the next exciting episode…


Here is a 15 minute video of my flammability tests of Kingspan K5 and Expanded Polystyrene.

It’s really boring but ‘highlights’ are

  • 3′ 30″: K5: Move blowtorch closer
  • 8′ 00″ : K5: Close up
  • 10′ 40″ : K5: Post Mortem
  • 11′ 25″ White EPS: Start
  • 11′ 57″ White EPS: Move blowtorch closer
  • 13′ 06″ White EPS: Post Mortem
  • 13′ 20″ Black EPS: Start
  • 13′ 57″ Black EPS: Post Mortem
  • 14′ 16″ Black EPS#2: Start with burner further away
  • 15′ 30″ Black EPS#2: Post Mortem

One Response to “I am becoming an insulation bore.”

  1. Ciro Alberto Sánchez Says:

    Thermally insulated.

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