If you are trying to decide between the two materials it s important to carefully look at the metal over shingle roof problems.
Metal roof on top of asphalt shingles.
It doesn t matter if the air space is a half inch or six inches because the condensation factor will remain the same.
Most codes now allow no more than two layers of roofing before requiring a complete tear off.
The purlins are screwed or nailed down to the roof deck depending on how the metal roofing manufacture has testing for their roofing panels and then the metal is installed to the purlins.
Both metal and shingle roofs are great options for your next roofing project.
3 install 1x4 purlins down over the shingles before installing the metal roof the third way to install a metal roof over shingles is by applying 1x4 purlins over the shingle roof.
As long as the plywood under the shingle roof is in good condition this way can provide many benefits.
So if your roof has two layers it may require a complete tear off even though steel is lighter than asphalt.
Metal roofs must be laid flat on a vapor barrier because steel will condensate if there s any air space underneath it.
Things to know about metal over shingle roof problems.
The second way to install a metal roof over a shingle roof is with the use of purlins or battens.
It is very much like constructing a non loadbearing interior wall framework and sticking that framework on top of your roof.
Put the steel down directly on a vapor barrier.
Can you avoid tearing off your old asphalt shingle roof by putting a steel roof over it.
This is by far the most common way to install a metal roof.
This method has its benefits as well.