I'm putting breathable underlay under a tiled roof. The slope of the roof is very shallow - about 15 degrees. The instructions are to lay the underlay loosely ie: let it droop between the rafters for a cold roof and not to pull it taut. But I'm concerned that on such a shallow pitch any dip is going to cause water to pond.
I know that the tiles are supposed to stop water penetration but again, on such a shallow pitch, I think wind-blown rain is more likely to get under them.
Should I be concerned about water penetration and, regarding laying the breather membrane, how loose is loose?
Thanks for any advice.