External insulation boards?

[cats_fandango]

Hi everyone I need a little help here and I'm not having much luck finding the answers on my random google quests..


Ok so to keep it simple..


My plan for spraying closed cell expanding foam insulation to the outside of my log cabin (behind an extra layer of cladding which is to be installed) (its basically covered in external studwork at the moment..) isn't going to be financially viable afterall (its a log cabin but a very large one)

I did however see the following video that presents a far cheaper option..

(basically the guy cuts insulation board to a slightly smaller size than the gap in the outside stud work, fits it and then fills the surrounding gap with expanding foam)

It appears (at face value) that this could indeed work and would be affordable, but I'm not 100% convinced (again at face value) that those boards he's using are waterproof enough that they won't just suck up moisture (I'm not familiar with the boards possible uses besides indoors..)

So, would I be correct? is there a better kind of insulation board I could use or would the one in the video be fine?
Or is the board fine IF I then wrap the building in a waterproof or breathable membrane? or a coat of weatherproofing paint on the exposed studwork? etc etc

Any help on my strange predicament would be great, thankyou








P.S/ and for anyone who may wonder why the hell the outside would need to be insulated..
The timber walls are very thin with minor gaps and spaces here and there inbetween planks and a simple coat of weatherproofing just won't cut it..

I ideally need a barrier between the wall and the elements that is waterproof and insulative enough that harsh temperatures won't deteriorate the walls (as I need the building up for quite some time to come..)
If anyone has any other alternative options, I'd love to hear them too

Thanks

 

[John D v2.0]

Those boards won't absorb water from the air. You needn't foam round unless you left gaps when cutting or the battens are warped.
Make sure you allow ventilation to the timbers behind your cladding. You want to make are things dry out quicker then they get wet. A plank of wood suspended by a rope in the sun and wind won't rot, but wrap it in cling film and it will.

 

[r896neo]

Kingspan etc would be fine for this, PIR is closed cell and so will not absorb water. Expanded polysterene in low densities like jablite will both absorb and wick moisture but as john says they wont suck it out of the air.

 

[geraldthehamster]

PU foam degrades in sunlight.

Cheers
Richard

 

[tomfe]

What the juice?
Spray foam would be cheaper than wrapping it in PIR surly. PIR is so much better the spray foam (don't listen to the Americans) it has an constant thickness, it is cured under correct conditions and it has a better thermal performance. The downsides are it's not as quick to install and is more expensive per m/2.
You'll have to leave a void behind your cladding what every you do to allow it dry, so you can use a breathable membrane to protect your insulation what ever you use. You could use cavity batts etc....

 

[^woody^]

That idea would work, but ....

The cladding should provide the waterproofing, but as this is not 100% resistant, there should be a minimum 25mm ventilated air cavity behind the cladding to allow drainage and ventilation for evapouration.

As you will be sealing the structure, it will be important to prevent any moisture getting into the walls from the room inside, so a vapour membrane would normally do this.