Onoff Posted May 2, 2020 Share Posted May 2, 2020 (edited) Over on a different forum people are putting up their workshop builds. One lad, just about to start so I suggest putting 150mm of insulation under his slab and some UFH pipes. For all weather comfort, future living space maybe etc. He comes back with "I've got some 50mm polystyrene, will that do?" I know anything's better than nothing but any idea of the percentage heat loss down through 50mm eps vs 150mm pir? Just to give him an idea. Cheers. Edited May 2, 2020 by Onoff Link to comment Share on other sites More sharing options...
ProDave Posted May 2, 2020 Share Posted May 2, 2020 I am not sure I would choose UFH for a garage even if it was well insulated. The elephant in the room being the garage door. My "insulated" roller door should fail the trade description act unless you count the 5mm of "insulation". In winter it runs inside with condensation. Link to comment Share on other sites More sharing options...
Conor Posted May 2, 2020 Share Posted May 2, 2020 50mm of EPS will be about 0.5 and 150mm PIR will be 0.12. huge difference. Our "garage" will be made with ICF and I'll put in 100mm EPS under the slab... Its more for keeping a stable temperature all year round rather than aiming to have it as a heated space. Link to comment Share on other sites More sharing options...
Russell griffiths Posted May 2, 2020 Share Posted May 2, 2020 If he has 50mm tell him to double it up to 100. Link to comment Share on other sites More sharing options...
Onoff Posted May 2, 2020 Author Share Posted May 2, 2020 17 minutes ago, ProDave said: I am not sure I would choose UFH for a garage even if it was well insulated. The elephant in the room being the garage door. My "insulated" roller door should fail the trade description act unless you count the 5mm of "insulation". In winter it runs inside with condensation. Sorry, just changed the thread title to Workshop which is what most are building. More glorified sheds than garages. Link to comment Share on other sites More sharing options...
Onoff Posted May 2, 2020 Author Share Posted May 2, 2020 15 minutes ago, Conor said: 50mm of EPS will be about 0.5 and 150mm PIR will be 0.12. huge difference. Our "garage" will be made with ICF and I'll put in 100mm EPS under the slab... Its more for keeping a stable temperature all year round rather than aiming to have it as a heated space. Thanks but what's that %age wise? Link to comment Share on other sites More sharing options...
Onoff Posted May 2, 2020 Author Share Posted May 2, 2020 2 minutes ago, Russell griffiths said: If he has 50mm tell him to double it up to 100. I'm assuming he's meaning ordinary eps. Doesn't eps/pir have to rated compression strength wise for under floor use? Link to comment Share on other sites More sharing options...
ProDave Posted May 2, 2020 Share Posted May 2, 2020 1 minute ago, Onoff said: Thanks but what's that %age wise? Didn't @Jeremy Harris calculate that with his floor U value 0.1 or better, he still lost 8% of his heat to the ground? Link to comment Share on other sites More sharing options...
Onoff Posted May 2, 2020 Author Share Posted May 2, 2020 6 minutes ago, ProDave said: Didn't @Jeremy Harris calculate that with his floor U value 0.1 or better, he still lost 8% of his heat to the ground? 300mm of eps I think he has? Link to comment Share on other sites More sharing options...
Jeremy Harris Posted May 2, 2020 Share Posted May 2, 2020 9 minutes ago, ProDave said: Didn't @Jeremy Harris calculate that with his floor U value 0.1 or better, he still lost 8% of his heat to the ground? Yes, I did. Here's a fairly simple calculation spreadsheet that may help, although I'd not get too hung up about percentages, as when you're only putting about 400 W of heat into the floor, the loss of about 32 W of it isn't really worth worrying about too much: Floor heat loss and UFH calculator.xls Link to comment Share on other sites More sharing options...
Russell griffiths Posted May 2, 2020 Share Posted May 2, 2020 7 minutes ago, Onoff said: I'm assuming he's meaning ordinary eps. Doesn't eps/pir have to rated compression strength wise for under floor use? Eps 70 is the normal standard, like the stuff they sell in wickes this is fine for under a floor if it’s some left over packing crates it could be less. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted May 2, 2020 Share Posted May 2, 2020 Our underfloor insulation is EPS100, but that's probably as much to do with the availability of large, thick, sheets as anything else. The actual load on it is around 6 kN/m², so just 6% of the max compressive load rating of the insulation. The reason for this low loading has a lot to do with the way that EPS compressive strength is defined, as the limit figure is for 10% compression, which would mean that a 300mm thick layer of insulation would move about 30mm when loaded to it's maximum, which would be unacceptable. In general it seems that the loading is derated to be below about 10% of the maximum allowable, in order to minimise movement. Link to comment Share on other sites More sharing options...
MortarThePoint Posted June 6, 2020 Share Posted June 6, 2020 Bit late to the party here, but our Structural Engineer specified Kingspan GG300 for our garage as it has higher load bearing It has Compressive strength = 300 kPa (at 10% compression) https://www.kingspan.com/gb/en-gb/products/insulation/insulation-boards/kingspan-greenguard/kingspan-greenguard-gg300 Link to comment Share on other sites More sharing options...
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