Insulation

[joycey]

Hi,
plan on insulating my transit and using it to sleep in occasionally.
am fitting a a rotating etractor fan (fletner tcx-2)
using 1" kingspan (solid foam boards with foil cover) glued to metal panels

my question is what to use as a moisture barrier

1) breathable membrane as used in houses (black and blue felt like stuff)
or
2) a plastic membrane that is not breathable

6mm plywood then over the lot
cost is not an issue as I have both available (leftovers from various family builds)

thanks,
pj

[MrMPuk]

Breathable membrane will let moisture through.

[chris07]

Breathable membrane will let moisture through


tyvek wont

[MrMPuk]

Breathable membrane will let moisture through


tyvek wont

I'm pretty sure that the idea of a breathable membrane is to let moisture through. Which Tyvek product are you talking about?

[chris07]

45mx 1m. Breathable, high-performance pitched roof underlay made from polyolefin materials, producing high vapour permeability and water-resistance. User friendly.
Eliminates Roof Space Ventilation

this stuf works wel i use it on all the roofs i do

[MrMPuk]

45mx 1m. Breathable, high-performance pitched roof underlay made from polyolefin materials, producing high vapour permeability and water-resistance. User friendly.
Eliminates Roof Space Ventilation

this stuf works wel i use it on all the roofs i do

That lets moisture through so is no good for this job.

[Missile]

45mx 1m. Breathable, high-performance pitched roof underlay made from polyolefin materials, producing high vapour permeability and water-resistance. User friendly.
Eliminates Roof Space Ventilation

this stuf works wel i use it on all the roofs i do

Breathable materials allow for water vapour to pass from one side to the other implying that the outgoing side has to be permeable which your van roof being metal isn't. Water resistant isn't the same as waterproof and rooftiles are also permeable surfaces. You've got a metal impermeable surface in van that may have a film of condensation on the interior. You don't want that forming between your metal and insulation as one or both will rot or it will find a less desirable passage out. I'd be looking for a spray on solution like that used to insulate lofts but check that the chemical constituition is suitable for metal surfaces.

[stevew]

I'm with Missile. A spray on solution gives the best results as is stops condensation forming on the inside surface of the steel. However pray you don't ever want to remove it!
If you're fitting foam/polystyrene then you will get condensation and rust. Better to use a water resistant wool and a breathable membane to let the water out. I speak from experience in Narrowboats.
Steve

[craphippy]

had a vw t25 and found that dot dabbing with sika then ataching polystyrene to it did the trick on the sides of the van, giving a space between the panel and poly allowing any moisture to seap away through its own drainage channels

on the roof i used 9mm ply with a foil backed bubble wrap above that, sleeping in a van creates alot of moisture and the best way to combat that is have good ventilation ie extractor or leave the windows open a crack.

[bron y aur]

I wouldnt worry about condensation unless its freezing outside and the inside temperature is roasting , in anycase insulation should be bonded to the metalwork with no gaps between it and the outer skin, that way the inner temperature cant be the same as the outer, think about double, triple glazing effect.

[sc_BK]

What about stuffing rockwool type loft insulation in behind ply? Would that lead to rust?

[MrMPuk]

What about stuffing rockwool type loft insulation in behind ply? Would that lead to rust?

Without a vapour barrier yes.