This is a bit of a complicated question.
Metal roof without battens.
If you do not have good ventilation in the attic then i have some concern about installing the metal roof without battens.
The roofing is manufactured in panels that install using aluminum nails or screws that fasten the panels to wood stripping also known as nailers or battens.
This great question comes from edward c a homeowner who plans to have a new metal roof installed over the aging existing shingles on his single story home.
As a great option to the expense and bother of battens there are concealed fastener metal shingles shakes and tiles available.
Types of roof batten systems.
It sounds like the metal panels you re installing probably have a great deal of contact with the underlayment unless they are installed on top of battens.
Whereas many older metal roofs or metal roofs on larger buildings have been successfully installed over battens rather than solid decking it is the clear preference for residential applications that metal roofing always be installed over solid decking to avoid dangerous and damaging condensation issues.
This is the case with most vertical seam products.
Metal roof installations without an air gap are done all the time.
Thanks edward for allowing me to share our correspondence on this frequently asked question.
Roof battens are thin strips of material that may be made of wood plastic or metal.
This creates a thermal break which is very similar to a vertically seamed metal roof installed on battens.
Can a metal roof be installed over my existing shingles without the use of battens.
In most cases there is nothing about a metal roof that increases the need for ventilation beyond what is needed for an asphalt shingle roof.
The key in most cases is having a properly vented attic beneath that.
Note that you can have a metal roof.
For example elevated battens are standard wood battens that have a block of plastic in some cases wood attached to the underside to elevate.