Insulation and Vapour Barrier advice

penguin00

Hi,

I am about to job to do a DIY revamp an old mobile home. Its current construction from inside out is a thin timber panel 40mm timber frame lapped horizontally and vertically with the usual aluminium covering.

I am getting confused with talk from different sources with regard to the following.
Vapour Barriers (I am thinking this is form of Polythene sheeting allowing no passage of air or vapour or moisture).
Vapour Control Layer ( a sheet membrane with tiny holes which will allow air and a controlled amount of water in the air to pass through from warm air inside to the colder air out side.
Breather membrane (this is used to cover timber sheets like OSB on an external wall my thinking here is its only used on the cold face of the external wall / roof and its purpose is to prevent moisture coming through from the outside to the OSB while allowing the warmer moist air from the inside pass out )

My first question is I suppose am I correct in the meaning of all the above?

The reason I ask is to decide what I will use in the re vamp.

This is my plan at the moment
For the walls I plan to pull off the thin timber panel and replace it with a 6mm WBP ply to strengthen up the frame. I then plan to fix maybe a 50mm or a 60mm insulation board (Kingspan type) to this then place a Polythene sheet as the Vapour barrier by securing it with a 25mm x 50mm batten and also use this as a space for wires then fix the plaster board. All old windows will be replaced with PVC windows.

For the floor I plan to pull up the old ply floor as there has been water damage. Fix insulation Size and type depending on the depth of the joists with netting or clips keeping some space for air to circulate underneath. Fit a Vapour Barrier polythene sheeting on the warm side of the insulation over the joists taped up to the wall Vapour Barrier and re floor with ½ inch WBP ply then some type of laminate flooring or tile.

The roof is aluminium sheeting curved in profile. I plan to spray foam the underside of this leaving conduit for lighting wires. Then place a vapour barrier polythene sheet and taped down to the Wall Vapour Barrier and then fix plasterboard.

With all this trapping of Vapour on the inside I realise I will need to fit a good few hit and miss style vents.

In the future I plan on pulling off the external aluminium covering spray foam insulate the existing frame to increase the insulation to 90mm or 100mm fix another sheet of maybe 9mm OSB and a breather membrane fix cross battens and then a final wood cladding.

My other questions are am I mad using all these Vapour barriers instead of Vapour control Layers?

Could it cause problems in the future with mould/rot or the ply floor rotting because of the vapour barrier underneath it?

Could I use OSB 3 instead of WBP Ply in the walls if its cheaper?

I know it’s a long post but any advice or comments would really be appreciated.

Thanks.