Venting stud walls

[Sjb]

Just taken delivery of my rather large new garden workshop/gym/sauna today and starting the insulation process soon so I don’t freeze my knackers off this winter like I did in my prefab concrete draughtbox last year.

I need some advice though, I’ve done lots of reading on kingspan, air gaps and vapour membranes this afternoon once it was built and the only info I can’t find is what to do if the stud walls are already sealed to the external cladding, I understand the need for an air gap behind the insulation so air can move behind the cladding but what do you do with a sealed stud? I don’t really fancy putting 30 odd high and low vents in every stud panel as it will look pish. I have a 70mm gap from face of stud to back of cladding, original plan before really researching was 70mm kingspan everywhere I can get it then internal cladding. Any ideas much appreciated and thanks in advance.

 

[Sjb]

Pics for reference

 

[Sjb]

And again

 

[Sjb]

Also it could be said that it is way too big on the front, my other half has gone mental so in the next few weeks the pent roof will be made into a flat roof so it doesn’t look so imposing.

 

[Beau]

You will surly get some ventilation through the shiplap. If it were me I would fill the gaps between the studs fully with Celotex/Kingspan and then fill any voids with expanding foam (gun grade and gun easiest). Then foil tape over all joins to make doubly sure vapour cant easily get in behind the insulation but I do think you will get some natural ventilation anyway. Bare in mind you are going to have thermal bridging on the studs unless you have another layer of insulation bridging them.

 

[Sjb]

Would you put a 20mm batten inside the studs for an air gap and go for 50mm kingspan or fill the whole gap?

 

[Beau]

Cant see you need another batten. Just a 25mm sheet of insulation and fix your inner paneling right through to the studs.

My understanding of the potential problem is warm moist air being able to quickly get to the outer surfaces which are cold. Then you get condensate which could lead to rotting. If you are careful with the insulation and taping there is no fast passage for warm moist air to get to the cold surface so no issues. Hence the recommend for a vapour barrier to cover for poor construction.

I should add I am only a self builder and not a pro but our roof was done much as I describe many years ago without any problems to date.

 

[MARK.B.]

Cant help with the insulation,but if you can sweet talk your wife around to keeping the pent roof,flat roofs are a pain.