Ventilating Insulated Roof with Battens
I have the following layers on my insulated roof (conditioned attic) under construction in climate zone 3 Southern CA – (currently in sheathing, underlayment stage): rockwool between attic rafters, existing skip sheathing, FR10 fiberglass slipsheet, 3″ polyiso insulation, 1/2″ CDX plywood with taped seams (Siga Wigluv tape), 2 layers G40 (SBS modified fiberglass underlayment), lightweight concrete tile.
The roofer is accustomed to installing the tile without battens in our area on low/moderate pitch roofs. However he usually doesn’t do cool roof designs. So at the moment the design is without battens.
But wouldn’t it be better to install battens (and counter battens) to keep the underlayment from cooking? If I understand correctly the insulated layers will make the underlayment much hotter than a conventional roof that has a vented attic.
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I'm not aware of any studies done with concrete tiles, but studies done with fiberglass shingles show that shingle color is more of a temperature driver than roof ventilation. I expect that this would be the case with concrete tile as well. Any tile system (concrete, clay, etc) is relatively well ventilated through the airspaces between individual tiles. I doubt that the existence of battens will have much effect on the temperature of the underlayment, but they wouldn't hurt either.
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