Insulation trapezoidal sheet flat roof with clamp fleece and OSB

Hello everyone,

first of all, I want to introduce myself:
I’m Markus, 35, from Upper Franconia and after 15 years in beautiful Rosenheim, I am now back home to renovate/prepare my house and farm here.

I have a special question for which I would like to hear a few different opinions:

I plan to convert an old tractor garage into a (hobby) workshop.
The floor area is 10 x 7m, masonry all around with a roof made of trapezoidal sheet metal, sloped about 5°, and 3 large doors.

Now I want to insulate the roof.
Although I will only heat the hall sporadically (probably using a warm air heater/blower), I want a certain efficiency and not to let the heat escape directly through the metal.

Currently, the structure is as follows:
- trapezoidal sheet metal
- 70/40 battens
- 130/90 rafters (spacing about 90cm)

I would like to work here with 120mm insulation wool and OSB boards (visible).
I have read that OSB 3/4 can act as a vapor barrier if the joints are sealed. How would the wall connection then be executed?

Would that be sufficient?
Because then I could save the money for the vapor barrier and the battens as well as the filling & painting of the drywall panels.

Many thanks in advance and best regards,
Markus

Hi

Somehow I don’t like your planned structure.
What happens to any condensation that might occur under the metal sheets? That then drips into the insulation.
Have you calculated the structure?

From my gut feeling, I would remove the metal sheets and roof battens, install a DWD board, counter battens and roof battens, and then the metal sheet.

Olli

Hi Olli,
thanks for your answer.

I actually wanted to avoid removing the roof...
Attached is the calculation from the U-value calculator.
I hope I entered everything correctly.

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Do you think there will be enough condensation to cause dripping?