Insulating under suspended chipboard floor - vapour barrier question.

[rossendo11]

I have a house built in 1984 in Scotland. It is a timber frame house sat on brick foundations and has concrete blocked outer walls. There is a 70cm solum under the suspended floor, with a bitumen layer on the earth below. The solum is very well ventilated with a number of air bricks.

I plan to do the following:

• Rip out my existing t&g chipboard floor (it creaks like hell and isn't level)
• Add mineral wool insulation between the joists, suspended in a breathable membrane
• Replace chipboard flooring, glueing and screwing down to the joists
• laying an underlay for laminate
• Laying laminate floor on top

My question is, where should the vapour barrier go? Does it have to go under the chipboard flooring (least preferred method as i cannot glue the flooring down, and won't be able to see the joists as i lay the floor) or can i just use a vapour barrier underlay under the laminate flooring and save a step? I thought that logically if the underlay is sealed and taped, then this could be enough to prevent the moisture from passing from the air in the house to the timber/insulation below..?


I would really appreciate thoughts on this! Cheers.