Hi All,

Apologies for another 'what type of insulation to go for?' question. At least I know I am having 225mm!

This is for a SIP extension to a 1950's bungalow, so my exposed perimeter has been reduced by 6m.

Just wondering what flavour of insulation to go for on top of my 225mm slab. I am restricted to 225mm of insulation as I need to match the ffl of the existing bungalow (something the architect almost forgot about!!).

My floor buildup will be:

Retrofit UFH system
75mm screed
225mm insulation
225mm Piled slab
50mm insulation
cellcore HX Plus

My architect specified Celotex FR5225 - is that FR5000 @225mm? I've checked the Celotex calculator and that suggests I use FF4000 because of my UFH. This gives me a u-value of 0.14 (but their calc only allows a max of 125mm).

Kingspan with 175mm (kooltherm k3) shows u-value to be 0.10

My P/A ratio is 0.509

I'd like to achieve a 'good' u-value (certainly better that Buildregs) But I also realise that Celotex isn't necessarily the cheapest or most suitable option always. Very little of the insulation would be below ground level so I'm not leaning towards EPS specifically either.

Bit bamboozled by the different options available.

Any suggested products would be appreciated.

OB

Under slab is a prime place for seconds quality kingspan; sho cares if the boards are bent/wobbly/missahped when theyll be covered over with smooth screed and the screed will take out undulations

yes to platinum being the grey/graphite eps

Posted By: kentishgreenThanks Tony - by 'platinum' this would be top of the range EPS/essentially any EPS with the word 'platinum' in the title? Contains graphite and is usually grey? I;ll start pricing up with Kore, Springvale and my local merchants

Platinum is graphite, others are carbon black. There's a difference

''Platinum is graphite, others are carbon black. There's a difference''

Saint. Thanks for this. Can you elaborate? Is the difference in the lambda?

"Yes, I had actually been looking at Seconds & Co. My only concern would be that the boards are so undulated that the screed would'nt sufficiently compact it down, so that rather than 75mm of screed I would have maybe 50-65 mm of screed and a cavity under the EPS. I'd be okay with edges that are a bit bruised. Maybe I'm over cautious?"

First off, kingspan doesn't really compress. Your screed is going to be in the region of 100 to 150kg per square metre so it'll end up solid but if you're expecting a high spot to squash, it won't. It doesn't bend much either when it's thick, but you could stack 4x50mm sheets for more flex than 1x200, for example. You need to get the sand blinding flat, accept that you're still going to get slight mounds. The bigger your sheets, the more they will pick up on a mound. The only way you can get a shortage of screed in an area is if there is a mound, then you have thin screed, thick insulation and a mound in the sand so you don't have thin screed over a cavity

I was going over an existing slab. I put sand blinding down and used a self levelling laser, plus a tape measure on a stick to measure spot heights and got the floor mostly level. The seconds boards I got were occasionally a bit bowed and wonky, and they were all 1200x600 in size, which helped not only in manhandling but in levelling out. Whenever I found a board that see sawed a bit I slashed along the fulcrum with a Stanley knife and stamped on it so it broke and adopted the form of the floor Underneath

Tony is right in that you do have to be careful with what you get from seconds n co. Their boards are pretty much priced by eye rather than any science and the result can be more than straight kingspan. Equally there are some real bargains, most of my stuff was between a third and half the price

Posted By: Nick Parsons''Platinum is graphite, others are carbon black. There's a difference''

Saint. Thanks for this. Can you elaborate? Is the difference in the lambda?

Yeah, this is news to me?

Posted By: CWatters

300mm of lightweight insulating screed will give you an R value of approx 4.5 m2K/W as an alternative to 225 Celotex plus 75mm screed. Slightly less efficient perhaps but a single pour and one tenth of curing time versus conventional screed?

Don't put UFH in insulating screed.

Absolutely!
The original posting refers to a "retrofit UFH" above a 75mm screed and 225mm insulation. The insulating screed replaces the insulation as well as the 75mm screed beneath the UFH system

''I suspect this is a red herring''

Nah! Definitely one or other shade of grey.

Posted By: fostertomSecond, Platinum is a trade name - so are you sure there's really a technical difference we shd know about, between 'platinum' and 'carbon black'? How to recognise - is it just light vs dark grey? In suspect this is a red herring.

I didn't say platinum vs carbon black I said graphite
Yes Platinum is the brand name used by EPS processors using Neopor from BASF its based on graphite. Sunpor also uses graphite (Lambdapor etc) whereas Ineos Styrenics use carbon black in its Silver range. Its in the spec sheets.
Maybe this is all a bit too insulation anoraky.....

Tom, the difference is marginal but Platinum (Neopor) shows lambdas of 0.030 to 0.031 W/mK depending on the processor whereas Ineos Styrenics' Silver is quoted at "about 0.032 W/mK" i.e. 1-2 milliwatts difference