What's the proper way to build a metal pitched roof?

[jamie_]

Hi,

I’m planning to build a music studio in my garden.. I’m 80% there with the design, but need some advice regarding cladding the roof.
The plan is for a pitched roof design and I want to use either box profile or corrugated metal sheeting to clad it.

I’m thinking from an acoustic and thermal insulation perspective, to go for a decent thickness of PIR insulation between the rafters, then a layer of OSB on top, then a membrane, but I’m not sure of the correct way to then attach the metal sheeting on top.


All the manufacturers guidelines I can find for this type of material suggest attaching it to thick purlins, but they are all aimed at building a barn or workshop roof with no mention of wood sheathing or insulation below. I've found several videos on youtube (all from America), where people are using metal roofing on houses and are laying the metal directly on top of the membrane (on top of the OSB) and are also using foam packers at the ends, but I feel like restricting airflow beneath the metal might be an issue?


Basically my question is:
On top of the joists should I go OSB>membrane>metal roofing sheet or OSB>membrane>some sort of battens (or thick purlins)>metal roofing sheet.
I feel like any sort of horizontal battens will prevent any drips from running downhill, but having no battens might restrict airflow. What’s the proper way to do this?


Thanks,


Jamie

 

[noseall]

As far as I know, metal clad buildings are constructed so that there is the outer metal skin - insulation - then a secondary containment (liner) layer, thus creating a sandwich effect. No gaps that I'm aware of. Others use pre-insulated metal sheets.

 

[^woody^]

You'll need battens and counder-battens.

Whether its best to have a vented void or insulation is a matter of design, for which you should contact the roofing sheet manufacturer for guidance.

Also see the Onduline over cladding system for something similar.