Insulate attic with metal roof

[jnel]

Hello,

I have just bought a house with standing seam metal roofing. I am going to demolish the current upper floor and redo the insulation.

The house I have now has a list-coverage (felt) which from the outside looks like this:

• Felt, tongue and groove planks, 35mm air gap, masonite, insulation, vapor barrier, plaster

Since the new house has a metal covering with masonite just under the metal, I'm a bit unsure about how the setup should look if I were to tear up to the metal and rebuild.

Like this, perhaps?

• Metal, masonite, air gap, masonite, insulation, vapor barrier, plaster?

 

[jnel]

No one has anything smart to say?

What actually concerns me is whether there should be an air gap on both sides of the hardboard, that is, between the sheet metal and the hardboard, and also between the hardboard and the insulation.

Sheet metal -> air -> hardboard -> air -> insulation

or

Sheet metal -> hardboard -> air -> insulation

 

[Larsa]

If it is standing seam metal roofing, shouldn't there be tongue and groove boards underneath? You must have some kind of underlayment, right?

 

[jnel]

Well. The undersheathing is made of board (masonite). I assume there are battens between the seam sheet metal and the masonite. (I’ll crawl up and take another look tomorrow evening)

The fact that the undersheathing isn't made of tongue and groove planks (which seemed completely natural to the inspector) makes me unsure about what the correct procedure is and what I should aim for now that I am renovating the upstairs and will be re-insulating the roof.