Vapour barrier or not?

[Tylerz]

Hi I'm after advice on an insulation project I'm about to start. I've got an old mobile home with typical aluminum cladding then basic polystyrene boards between structural battens, then 2mm wood sheet walls. There is no vapour barrier fitted.
I'm planning on adding celotex boards to the inside using adhesive then cladding them with something like more 2mm wood sheets or maybe tung & groove.
Im thinking I will fit a heat recovery unit for fresh air in winter.
Am I going to have condensation issues or does the polystyrene act as a barrier?
TIA.

 

[noseall]

Celotex board sandwiched with foil can form an effective VB as long as the boards are not compromised. We'd use foil tape and foam to seal any joints or electrical exits etc. Dunno if all that tape will make a noise though once the van starts flexing..?

 

[^woody^]

If there is no vapour check layer now, then you wont need one when the insulation is changed, as you are not altering things.

However foil tapping joints would be good practice regardless, as would foam filling any excessive gaps if you can't cut the insulation perfectly.

 

[noseall]

foam filling any excessive gaps if you can't cut the insulation perfectly.

You don't trust his cutting/fitting.....

 

[RonnyRaygun]

I'm actually refurbishing a narrowboat at the moment and I noticed when I stripped out that there was no vapour barrier of any description behind the cladding. Due to this, the unprotected steel hull had a fair bit of flaking rust on the inner face. This won't be an issue for your aluminium but goes to show what vapour can do if left unchecked and allowed to pass through unobstructed.
I've now installed additional insulation and foil all over to help prevent further deterioration.
Some people have suggested that the vapour that passes through the cladding will be trapped and cause warping of the timber cladding. Not sure if that's going to be an issue or not but something to consider anyway.

 

[noseall]

If there is no vapour check layer now, then you wont need one when the insulation is changed, as you are not altering things.

Bit of an odd response. It wasn't a B'Regs compliance question. I'd be more mindful perhaps to suggest that if there is zero black mould or staining present then....

 

[Tylerz]

So there's nothing I need to add, the foil on the celotex works as a barrier & the batons are kind of ventilated so shouldn't get too damp?

 

[^woody^]

Bit of an odd response. It wasn't a B'Regs compliance question. I'd be more mindful perhaps to suggest that if there is zero black mould or staining present then....

It wasn't a bregs response, just a fact.

 

[^woody^]

So there's nothing I need to add, the foil on the celotex works as a barrier & the batons are kind of ventilated so shouldn't get too damp?

Does it get damp now before the refurb?

 

[noseall]

Does it get damp now before the refurb?

Bingo!

 

[John D v2.0]

They are changing something though, they're increasing the insulation!
If you add insulation you make things colder towards the outside. That's why condensation risk analysis exists.

 

[^woody^]

The outer edge will be just as cold as it always was. However for argument's sake, if it will be cooler at the outer edge then condensation risk is less than it is currently, not more.

But the increase in insulation is not a change for this situation, the structure is still as it was - inner lining, insulation, outer lining. If that worked before it will work after.

 

[noseall]

If ever there was a call for a VB its in this instance, especially considering it's a metal structure and all.

But the increase in insulation is not a change for this situation, the structure is still as it was - inner lining, insulation, outer lining. If that worked before it will work after.

What makes you think the mobile home has been parked or always will be parked and used where temp's are ambient. Stick an aluminium box out during a freezing cold evening then fill it with moisture making humans. Walls wetter than a bill-pastes' bucket!