Counter batten A batten laid in the opposite direction to tile and slate battens fixed to the rafters. Usually nailed over a boarded and felted roof to provide a space to stop water ponding at the normal battens.; Couple close roof A short span roof with ceiling joists as ties but no...
That being said, batten seam would be your best option, if you would like to try to install a metal roof over battens. If the crew succeeds in installing battens over the asbestos shingles, then this might be a viable option. Although, I still prefer the removal of the old roof ...