Suspended Timber floor Insulation - Graphite EPS?

stevebn

Hello:j,


New to the forum here!


I'm trying to find a cost effective way of adding insulation boards between the joists in the crawl space under my houses' suspended timber floor.


I've come across the usual Celetex/Kingspan options, but I've also come across Grey Expanded Polystyrene (EPS) boards which appear to be a third of the price with similar insulation properties!
Does anyone know if there is a reason I shouldn't go ahead and use the graphite EPS? I feel like I'm missing something here!


Any advice appreciated :beer:


Thanks,


Steve

Furts

Once upon a time EPS was used as a cavity wall insulation. However the Celotex/Kingspan products are vastly superior for insulation, strength, damage and having a foil surface. However they cost more.

You have to weigh up your attitude to cost versus insulation. If cheap is your criteria then go for EPS. But if you factor in an upgrade on the EPS, say using 150 -200 thick to match against 100mm Celotex then matters get more complicated - you have to weigh up where you stand here.

stevebn

Thanks Furt, great information. As a side note I!!!8217;m limited to about 100m by the joist depth so maybe best just going with the best insulation for that depth. I think I!!!8217;m getting a little confused by the insulation properties as they seem similar. I suppose the foil layer on the celotex may be a bit better with fire proofing as well. Hmmm

Furts

At 100mm I would be going for what is cheapest from your local builders merchant. Here there is no simple answer - the insulation is expensive to transport from the factory - lots of air really so in theory a factory close to you should be the cheapest source. But the builders merchants have national brand name suppliers.

I do not like EPS because of the fire risk and wastage, The alternatives will burn - think Grenfell Towers. But from a building site perspective it is not easy to make these products catch light - it takes much more persistence and heat than with EPS.

FreeBear

Any cables running under the floor ?

If so, you want to keep EPS away from them. EPS has a habit of leaching the plastisers out of PVC insulation (although modern cables are better).

As for the fire risk of EPS compared to Celotex/Kingspan PUR boards - They both burn very well, and both give off toxic fumes. I'm not sure EPS is easier to set fire to compared to PUR. Dropping a match on either will set both on fire.

stevebn

Yes there are quite a few cables running under the house. I'll be sure to protect them in some way. Excuse my ignorance but is Jablite (sold by B&Q) EPS?


Thanks,


Steve

Furts

stevebn wrote: »

Yes there are quite a few cables running under the house. I'll be sure to protect them in some way. Excuse my ignorance but is Jablite (sold by B&Q) EPS?


Thanks,


Steve

Yes, and Jablite has been around for donkeys years so is an established known brand. This was the product used as cavity wall insulation way back, but was superseded by Celotex/Kingspan because of the better performance with these products.

FreeBear

stevebn wrote: »

Excuse my ignorance but is Jablite (sold by B&Q) EPS?

For the price that B&Q sell the Jablite EPS for, you can probably get Celotex/Kingspan PUR boards for a similar price. You will also get a much better thermal insulation with the PUR products.

e.g. EPS thermal conductivity is 0.034-0.038 W/m-K, where as PUR is 0.020-0.023W/m-K (the lower the figure, the better).

Have a read of this - http://kingspaninsulation.co.uk/getattachment/dd80b3a0-ba1f-428f-9208-c4248d3a8557/Everything-you-wanted-to-know-about-Insulation.aspx

stevebn

Thanks for the info! Useful document.
I'm probably going to have to cut up whichever PUR boards I get to fit in-between the joists, but i'm planning on using foil tape to cover the gaps between the boards and the joists. Heard this may cause dampness issues as it effectively will make it air tight? not sure if anyone has any experience of this.

Keriou

Without knowing the age of your property, I assume it is 'modern' as you say the joist depth is just over 100mm? which sounds very small. Airflow below suspended timber floors is vital to maintain an appropriate moisture level in vulnerable elements like timber soleplate, joists and underside of floorboards so there may be a risk by insulating the floor but especially so if using a rigid material. Sheep's wool or wood wool would be more appropriate as they both allow vapour to pass through whereas rigid insulation may cause condensation which will increase the risk of decay to the timbers below. Have a look at heritage-house.org or heritageanddesign.co.uk for some good, free advice on insulation and causes of dampness.