laying engineered flooring, question about surface under

[happyhero]

Hi I have bought some Engineered oak flooring and the guy in the shop sold me some silver sided foam stuff to go underneath. I explained to him it was for out bedroom on the 1st floor of our house and it was a joist and floorboards floor.

At the moment there is carpet and underlay which I will remove, under this there is hardboard sheets pined down and looking underneath this most of the floor is pretty good but there were a couple of high points which I removed the nails and played about with the joist underneath and the floorboard itself planing a little to get it to a reasonably level surface and screwing the floorboards back down.

My question is should I or can I leave the hardboard and put the foam underlay on top of this?

I was just thinking that maybe leaving the hardboard down gives an improved surface and maybe offers a little further insulation but I want to know if maybe there is a reason not to leave it in place or if it will be a better job without it for some reason, I basically want to do the best job possible.

The floor I am laying will be a floating floor the guy in the shop explained to me.

Any advice appreciated.

 

[Irnbru72]

When I laid my engineered oak over my floorboards I just put sheets of plywood down as my floor was all over the place, made it slightly more level, I then put down the green underlay boards, then the engineered oak.
I'm sure it would be fine to leave the hardwood boards and then the underlay but there's probably more experienced guys on here than me.

The silver stuff is usually for concrete floors I think, to stop any damp coming through.

 

[foxhole]

Hardboard is fine under the floor, silver insulation is a general purpose for any application [and is supposed to offer modest heat retention.]