Mrs MTG has bought a transit van and had some bonded windows fitted in the sides.
It’s already ply lined on the sides, so I want to tidy that up and ply line the roof as well.
It makes sense to insulate it at the same time, so what’s best to use?

A 2.4×1.2m board of 50mm Celotex (the hard crispy stuff, similar to Kingspan) is £23 with my B&Q trade card.
I’d prefer to use this, as it’s water proof and I would imagine condensation can be a problem with a metal body, so any of the roll type loft insulations would end up soaking wet and useless.
Polystyrene is cheap, but I’ve seen how much smoke it makes when burnt, so I don’t like the idea of using it in a confined space. Are the modern versions any better?

If you get the 25mm stuff you will be able to slightly bend and flex it to the panels a little easier.

I can get quinntherm for £9 a sheet locally – try a decent size timber yard/builders mechant

+1 for 25mm.

50mm is pretty thick, eating up space and it’s not as compliant.

Use a jack saw to cut it, and use the saw to make easing cuts across half the thickness to help with bend radius.

Use the 25mm Celotex but bond in place with expanding foam, then there is no air to metal contact. You can also fill the structural sections sections too.

Buy a box online, should be enough for a van. LINK

I used a combo of 50 & 25mm celotex/kingspan, foil backed underlay and laminate floor insulation.
[url=https://flic.kr/p/7BoeXd]50mm Foam & lots of Underlay[/url] by Mike Smith 79, on Flickr
[url=https://flic.kr/p/7BodNj]Van Conversion – Underlay[/url] by Mike Smith 79, on Flickr
[url=https://flic.kr/p/7Bjspz]Boarded with Laminate floor base & lots of underlay[/url] by Mike Smith 79, on Flickr

Roof was the toughest to do and lst to be done, ended up with hot water cylinder jackets

Iused recycled insulation made from plastic bottles and got it from B and Q, waterproof and doesnt itch and you can stuffit into small spaces you cant get rigid foam into.

Im also sure polyurethane foam will rust through metal from the inside , so plenty of prioimer on steelwork first.

The ribs on the side of the van are 75mm thick, so need to worry about 50mm insulation using up useful space.
The roof ribs are about 40mm, so I’ll pack the ply out to leave 50mm for the insulation.
Good point about scoring the back to bend it, I was going to do that with the ply on the top corners.
I’d never heard of Quinntherm before. It looks very similar to Celotex or Kingspan.
I can’t see that recycled plastic insulation on B&Q, but doesn’t it gradually pack down when used in a moving vehicle? Rigid boards sound better.
Good point too about the foam causing rust. Maybe leaving the boards with inevitable small gaps around them to allow some air circulation would be best.

you can get insulation in 40mm sheets – it would be worthwhile you find out exactly what thicknesses you need for all parts as it can make the install very easy

also you dont want any air gaps – you will just get condensation – tape up teh edges of the foam nice and tight with foil tape – if you are putting ply on top this complete combination will form a pretty decent moisture barrier

As above, no air gaps as you are then creating a rot trap.

I suggest you buy the gun grade foam, and a gun, and a can of the cleaner although it’s just an acetone aerosol. It’s very easy to control the volume compared to the hand held which are either on or off only. Bed the boards in foam in a similar way to laying tiles.

If there is no air then no moisture or oxygen either. Most of the boats I have worked on over the last twenty years insulated this way are still floating. The one that sank wasn’t due to foam corrosion.

Check to see if you have any commercial insulation sprayers local to you, a good company will be used to spraying barges, metal containers etc. could save you money and time.

can’t see that recycled plastic insulation on B&Q, but doesn’t it gradually pack down when used in a moving vehicle?

http://www.diy.com/departments/diall-loft-insulation-l8m-w370mm-t100mm/197658_BQ.prd?ecamp=ret_dtf_criteo_13649270

its a quilt not loose bead

Ah, thanks Project, I assumed it was just shredded in to granules, a bit like polystyrene beads. It’s more like old fashioned fibreglass rolls.
I’m guessing it would soak up water like fibreglass, so I still think I’m best off going with the rigid board type with expanding foam in the gaps.

I used shhepswoolminsulation and hemp from amdro 6 yrs ago when I did my t4. Stuffed into every nook and cranny. If there’s no temp differential across the metal as it’s insulated you shouldn’t get condensation. The t4 I had was galvanised anyways so no rust issues.