Quote:
Originally Posted by tevake
I don't know about going over the shingles with the metal, Baz.
I would have to tear off the old shingles, then proceed with the metal roof.
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I favor the system described in the photo if furring runs vertically and roof is ventilated at the eave and ridge (
to prevent the rot feared) for the following reasons. Air Cavities are important and so are back up layers.
Condensation, or in other words the "dew point" will be on one side or another of the metal roofing. No problem if condensation forms on the outer surface, it just rolls down the roof.
However in a typical temperate northern climate the moisture from the air will condense on the other side of the material, and it needs a path out to prevent rot.
Building system designs be they
wall or roof are continually moving towards a multi-layer system using air-cavities. The advantages are that both sides of the outer material are either cold or warm thereby preventing the typical delamiation (
paint peeling - etc...) issues and buckling issues from expansion and contraction.
Below a photo from a project I did last year, just to meet the picture posting requirement.
