Piglet What is the best underlay for engineered wood in a cold flat?

[sh77]

Suggestions appreciated! I was thinking 6 mm fibreboard and 3 mm foil insulation. Is that overkill?

is it a ground floor flat; or, is the flat below unheated?

is it a concrete floor or wood?

is it draughty, and why do you suppose the flat is cold?

is the floor currently bare, or carpeted?

Raise ground - unheated basement storage below. Wooden floorboards. Currently engineered wooden floor - took a piece of wood off and noticed gaps between floorboards. Current underlay is white foam (2mm). We are trying to insulate the flat as much as possible. Due to cost and baby at home, going under the floorboards to lay down rockwool is not looking viable.

you won't be able to add enough thickness of insulation to do much more than stop the draughts. Loft insulation for example is between 100mm and 250mm, so a 3mm or 6mm underlay won't do much, and the ticker it is, the more trouble you will have fitting doors and skirting.

you can get an underlay which is rigid foam with a relective foil backing, it will probably help a bit, but if the old boards are at all uneven or gappy, the green fibreboard, which is a bit thicker, will do better at hiding uneveness. I have no particular experience of this. A carpeted floor will be warmer.

Thanks piglet!