Seconds & co insulation

[jpmcq]

Our concrete slab is down & I am looking at how best to insulate.  I had planned to used 130mm regular PIR with UFH on top, covered by a 50mm liquid screed.  However, after a lot of reading it seems that it would be better to be around the 200mm depth for PIR but we don't have the room for that now.  Alternatively I could go for 120mm Kooltherm 103 but that is out of budget unless I can get it from Seconds & co.

 

The issue I have is that they say they can't tell me what code the Kooltherm is so I won't know if it's the one designed for floor use.  I've seen a few mention that they have bought from there so my question is, how do you get around that issue?  If they were to send the variant for wall cavity, would you still use it for the floor & would the wrong variant still be better that regular PIR?  Or is there is a way of telling which variant it is by the look or description?  I see on their site that they offer no foil, foil & tissue surfaces, I think 103 has foil on both sides but not sure about the other variants.

 

Any help would be appreciated.

[SteamyTea]

As a general rule, don't worry about the least significant number for the thermal performance.

For floors that are screed/cast over, the compression strength is really the important bit.

Two things happen when insulation is compressed, the thickness reduces and the conductivity increases.

 

Ask yourself if you really want insulation of unknown or variable quantity where it can not be rectified. 

 

As a general note, all too often people ask similar question about floor insulation, nearly always a sensible amount has not been specified, especially when UFH is used.

[ADLIan]

They're 'seconds' for a reason - they've failed quality control procedures. May not have correct compressive strength or thermal performance as well as dimension problems. May not comply with relevant manufacturing Standards. With no label you don't know what you're buying.

[nod]

It’s one thing that you shouldn’t scrimped on 

Seconds are ok for an office or shed 

[Nickfromwales]

Call them up and ask these specific questions before buying.

 

The majority I see just have the corners stoved in etc, and are otherwise a brand new board / panel. If you fill the gaps with an appropriate foam etc then I see no reason not to use them tbh.

[jpmcq]

19 minutes ago, Nickfromwales said:

Call them up and ask these specific questions before buying.

 

The majority I see just have the corners stoved in etc, and are otherwise a brand new board / panel. If you fill the gaps with an appropriate foam etc then I see no reason not to use them tbh.

 

I did & they told me that they couldn't tell me the code so I wouldn't know if I was getting floor, wall or roof insulation.

[Nickfromwales]

3 hours ago, jpmcq said:

 

I did & they told me that they couldn't tell me the code so I wouldn't know if I was getting floor, wall or roof insulation.

Ah. Without compressive strength indicated then this is limited.

 

A bit odd though, that there’s no details of what they themselves are purchasing. 🤷‍♂️

 

 

[jpmcq]

18 hours ago, Nickfromwales said:

Ah. Without compressive strength indicated then this is limited.

 

A bit odd though, that there’s no details of what they themselves are purchasing. 🤷‍♂️

 

 

They said that they know what it is but they're not allowed to pass that information on.  And as a customer, I can't request a certain type.

[marshian]

31 minutes ago, jpmcq said:

They said that they know what it is but they're not allowed to pass that information on.  And as a customer, I can't request a certain type.

Then I think I'd be avoiding them and going for a supplier of known and guaranteed suitable material

[saveasteading]

Re compressive strength. It would certainly be a concern if building walls on top of the screed. Also if intending a grand piano or perhaps gymn equipment.

Otherwise probably not.

 

Re damage.  If 2 layers are used and staggered then this should be a minor problem.

 

With or without foil faces? Doesn't matter unless facing an air gap.

 

Thickness? Surely they are as described?

 

Insulating property?   This should not be random and I wouldn't buy without knowing this.

[saveasteading]

On 11/06/2025 at 15:48, Nickfromwales said:

fill the gaps with an appropriate foam etc 

I don't think I'd bother. A tiny air pocket still insulates esp in the lower layer.

BUT perhaps there's a perception  difference in a commercial or diy application.

[bmj1]

I bought the phenolic stuff from seconds and co. Was equivalent to k103.

 

Great stuff. Great price.

[jpmcq]

55 minutes ago, bmj1 said:

I bought the phenolic stuff from seconds and co. Was equivalent to k103.

 

Great stuff. Great price.

Did you know what you were getting when you bought or just risk it?

[bmj1]

I'm not sure the phenolic stuff could be anything else, i.e. it couldn't be the cavity wall stuff as not the same dimensions.

 

I called them by phone and asked if it was equivalent to the k103...

 

My experience was the stuff was perfect, albeit the odd cosmetic damage.

 

Under the screed, it wasn't going to make any difference.

[BotusBuild]

I used them for 160mm PIR for our warm roof. Apart from cosmetic damage and some minor warpi g (cured by sandwiching between layers of OSB) it was fine. I walked all over it and had piles of OSB on it for a while as I was installing.

 

[jpmcq]

14 hours ago, bmj1 said:

I'm not sure the phenolic stuff could be anything else, i.e. it couldn't be the cavity wall stuff as not the same dimensions.

 

I called them by phone and asked if it was equivalent to the k103...

 

My experience was the stuff was perfect, albeit the odd cosmetic damage.

 

Under the screed, it wasn't going to make any difference.

 

but for example, kooltherm 107 (pitched roof insulation) is phenolic and comes in dimensions 2400 X 1200 X 120mm as does kooltherm 103, and these are the dimensions that I need.  Also, on the seconds & co website, if you go to the kooltherm section, it states 'Boards may be Kooltherm or Koolduct'.

[JohnMo]

When I did our floor (2x 100mm thick PIR layers and 192m² of each layer) it just wasn't worth the risk to get odds and ends of random stuff added to the mix. In the end shopping around got new factory fresh stuff, direct from factory at about the same cost when you include shipping - which was half a lorry load.

[ADLIan]

As the name suggests Koolduct is for insulation of A/C ducts and not for use in floors, walls or roofs. Not sure who would risk that in a floor under the slab or screed!

[bmj1]

I can't imagine anybody will be putting 100mm of phenolic insulation around their A/C ductwork...! It will surely be Kooltherm...

 

But, it could be K107 which has a reduced compressive strength - so that's potentially something to consider