If a natural slate roof is unfelted, does this provide any ventilation to the underside? I'd like to jam some celotex between the rafters, but won't be bothered if I need to install specific ventilation at eaves and ridge. The roof covering will probably be replaced in the next five years, when felt and specific ventilation can be added. I just want to still have the rafters in one piece when this happens.
The proposed layers would be:
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