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Workshop Floor Insulation


Onoff

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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 by Onoff
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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.

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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. 

 

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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.

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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?

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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? 

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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

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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. 

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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.

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