Polystyrene or PIR in concrete floor

[Wilbur1969]

I have done a search and couldn't find anything, so based on the premise that no question is a stupid one!!! We're getting ready to put the floor in our new extension, and building control have said it needs 100mm PIR under the floor slab, I just wondered if we can use polystyrene as an alternative or would we need to put thicker polystyrene boards in to meet the insulation requirement? I'm guessing its not a straight alternative as everyone would use it based on cost but I can't find a definitive answer, TIA

[JohnMo]

PIR requires 50% less buildup depth compared to polystyrene.

 

100mm PIR or 150mm polystyrene.

 

But I would look to maximize the depth of PIR, to get best u value I could.  You only get one chance, then it's all buried for ever.

[Nickfromwales]

 

@Wilbur1969 Use the search engine and you'll find a lorry-load of answer on this subject. Feel free to find and add to a relevant thread / topic and we can keep the library in good order  

[Nickfromwales]

 

[MikeGrahamT21]

1 hour ago, JohnMo said:

PIR requires 50% less buildup depth compared to polystyrene.

 

100mm PIR or 150mm polystyrene.

 

But I would look to maximize the depth of PIR, to get best u value I could.  You only get one chance, then it's all buried for ever.

 

And don't forget the upstand all way round!

[Dave Jones]

300mm of EPS cheaper than PIR.

[Polish Builder]

EPS and PIR are two different types of insulation materials, and they have different properties that affect their insulation performance.
EPS insulation has a lower thermal conductivity than PIR insulation, meaning it is less effective at insulating heat.
A 300mm layer of EPS insulation will have a thermal conductivity of around 0.038W/mK, while a 100mm layer of PIR insulation will have a thermal conductivity of around 0.022W/mK.
This means that a 100mm layer of PIR insulation will provide a higher level of insulation than a 300mm layer of EPS insulation.
However, EPS insulation can have other advantages, such as being more affordable and easier to work with than PIR insulation.
EPS insulation is also a more sustainable option, as it is made from recycled materials and can be recycled at the end of its lifespan.

[ADLIan]

Lower thermal conductivity = better thermal performance. Thermal conductivity of PUR is lower, better, than that of EPS. To get the same overall thermal performance 300mm of EPS would equate to about 175mm (not 100mm) of PUR.

[Dave Jones]

3 hours ago, Polish Builder said:

EPS and PIR are two different types of insulation materials, and they have different properties that affect their insulation performance.
EPS insulation has a lower thermal conductivity than PIR insulation, meaning it is less effective at insulating heat.
A 300mm layer of EPS insulation will have a thermal conductivity of around 0.038W/mK, while a 100mm layer of PIR insulation will have a thermal conductivity of around 0.022W/mK.
This means that a 100mm layer of PIR insulation will provide a higher level of insulation than a 300mm layer of EPS insulation.
However, EPS insulation can have other advantages, such as being more affordable and easier to work with than PIR insulation.
EPS insulation is also a more sustainable option, as it is made from recycled materials and can be recycled at the end of its lifespan.

wrong.

 

100mm celotex is WORSE than 300mm EPS.

 

the numbers for a 10mx10m room

 

100mm celotex = 0.177

300mm EPS = 0.116