Bedroom retrofit – insulation time

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Next step in insulating the bedroom was gluing the insulation batts directly onto the Diathonite skim.

Choosing insulation means reviewing a number of issues: 

  • Age of your house – if built before 1930 the house will be breathable, so your insulation must also be breathable. If not, then you risk creating condensation within the wall, which will degrade the materials over time.
  • Space – a frequent question is about how to manage the loss of space if insulation is added internally. In fact, unless your place is very small, I’m not sure you’ll notice. The optimum thickness is between 60mm and 80mm. You can go thicker, but there are diminishing returns. Take a look at 60mm – it’s really not much.
  • Sustainability – whether to go with sustainable materials that won’t cost the earth. The material we are most used to seeing is PIR, short for Plyisocyanurate (Trade names: Kingspan and Celotex ). It’s very efficient for its thickness, easy to get hold of and a little cheaper. However it is made from petrochemicals and plastic, so extremely bad for the environment. There are a number of options that are significantly better – wood fibre, sheets wool, mineral wool – plenty about this in my book, Beginners Guide to Eco Renovation.
  • Cost – it is true that sustainable insulation materials are a bit more expensive that PIR. However, there are many reasons why they are preferable – not least, safety. In addition to the petrochemical issue, PIR releases toxic gases over time (off gassing) and is more flammable. In fact, BRE (Building Research Establishment) are no longer willing to work with Kingspan and Celotex as a result of Grenfell.

What we did 

We went for a different form of wood fibre this time round – Gutex Thermoroom – in order to explore the options that have become available since we finished the rest of the house. The material itself was more dense than the Pavaflex used previously and could be fixed directly onto the walls, without the need for a carpenter to build a framework. One job less was alright by me!

We used 80mm of insulation which when coupled with the Diathonite – a thermal plaster – and the Lime Green Solo plaster with thermal conductivity of 0.054 w/mK gives us roughly 100mm of insulation. 

Wood fibre – sustainable insulation

Like all wood fibre based insulation, Thermoroom is fully breathable. This means it allows moisture and humidity to move freely so preventing condensation and mould. You can read a lot more about this in my book Beginner’s Guide to Eco Renovation.

Wood fibre does a good job of keeping the house warm in winter, reducing energy bills along the way. In summer the insulation absorbs the heat and releases it very slowly, helping maintain an even indoor temperature. So insulating is a great way to future proof your home and using sustainable materials stops you adding to the reasons why you need to future proof.

If sound proofing is important – for a noisy six year old or a kid who plays the drums – then wood fibre is the best way to go. It absorbs more sound than other forms of insulation. Apparently because of ‘the low dynamic stiffness and open pore structure of the wood fibres.’ Sounds as if that would take a long time to understand – so please go looking yourself if you want to. I’m out!

You can feel the difference

Sound is one way you can tell the job is being done. Each time I popped into the bedroom with a cuppa and a biscuit for Harry and Jack, I noticed how that the room felt and sounded cushioned. It really is like wrapping the room in a duvet.

It was a relatively quick job – just a couple of days – given the insultation batts were glued directly onto the Diathonite. Until – we hit a snag. We had bought just one batt too few. The Gutex Thermoroom had come from Ecological Building Systems, based in Cumbria so getting a quick delivery wasn’t an option. 

Fortunately, Unity Lime – our previous supplier – wasn’t so far away. They had a similar product that Harry assured me could be used to complete the job. So once again, I found myself on a mercy dash for insulation. This time on a pleasant summers’ day for just one batt, rather than a stormy January afternoon for as many batts as I could squash into the car. Thanks to James for letting me purchase just one batt and not get left with a whole pack that I needed to find a home for!

Harry was ready to add in the last piece on my return and the room was left for the weekend to dry and settle. Then it was on to the next stage.

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