In an un ventilated roof moist air is passed from the roof construction through the breather membrane out into a ventilated air space formed by counter battens.
Retrofit installation pitched roof.
This system would consist of a base clip variable height post and a purlin system that would create the required positive pitch for a new metal roof panel system says chuck howard pe president of metal roof consultants inc cary n c.
U value target u values normally achievable for the rafter level insulation of a pitched roof are between 0 20 0 16 w m2k depending on existing rafter depth and available space.
These new roofs can be either low sloped less than 2 12 functional roofs or high pitched greater than 2 12 architectural roofs depending on the expectations of the building owner.
Once these and other pre installation steps are successfully completed the low slope roof retrofit can begin.
Download the mcelroy metal retrofit roofing guide to learn more.