Metac + Kingspan kooltherm

New Insulator

Hi Guys,

Hoping someone can advise a pure novice.

Looking to upgrade the attic insulation at floor joist level. I was going to go for the K7 kooltherm board, cut it and place between joists but it was mentioned to me that because artic joist expand and contract depending on the time of the year gaps at the sides are inevitable.

Is this true?

Would anyone recommend the kooltherm board 20 mm below the joint height with a good layer of metac wool over that?

Thanks

lowkeys

I’d go for Metac or mineral wool as it moves with the joists. You will never manage to fully fill the small gaps in a PIR board.

WildCardDoW

Have you considered spraying?

The U values aren't that far off the other options.

I'd go with that or the wool for sure. The wool if you're doing it yourself anyway.

Calahonda52

Spraying is not the answer.
Would not be using any ...span stuff post Grenfell

WildCardDoW

Any reasons you're against the spraying.

I've talked to actual BER assessors and they back it as a solution. For a floor or roof you spray it on to breathable cards (with a gap for roof between it and felt).

E-Zero 500 is the stuff I researched and 150mm of it under a floor would offer roughly the same as 100mm in terms of u values.

I have a few tables I could probably share OP if you needed just from calculating u values for floor areas. I think they're correct.