Floor slab insulation. Test my logic please?

[SteamyTea]

5 hours ago, G and J said:

PIR instead of 120mm each of polystyrene and PIR

You are still comparing overall thickness though (I know you had a (expletive deleted) up are limited on thickness). 

What you need to do is pick a U-Value (i.e. 1.2 W/m².K) and compare the prices to achieve that, not compare prices to fill the gap up.

4 hours ago, saveasteading said:

10 year return would be my judgement

Not if you had made that decision in 2015, 6 years before our energy prices doubled.

[Roger440]

5 hours ago, JohnMo said:

But you also need to buy the correct grade for appropriate compression strength. Not all are equal.

 

 

 

Now thats a bit of a minefield if ever there was one...............

[Roger440]

2 hours ago, SteamyTea said:

 

Not if you had made that decision in 2015, 6 years before our energy prices doubled.

 Doesnt building control use 15 years as its guide as to insisting on stuff, at least in a retrofit situation?

[SteamyTea]

1 minute ago, Roger440 said:

 Doesnt building control use 15 years as its guide as to insisting on stuff, at least in a retrofit situation?

No idea.

Would be OK for windows and doors, but not very good for slab insulation.

[SteamyTea]

Use this simple cut out guide to work out your ideal insulation thickness for your desired U-Value.