Because waterproof shade sails are opaque the heat build up is quite considerable
Water ponds on the sail and will spontaneously dump a few gallons on whoever is near the sail
Typically shade sails high so the rain protection is only from vertical rain, bit like an umbrella will keep your head dry but not much else.
Our customers' experience with outdoor dining spaces is that usually in colder climates heavy rain is associated with a temperature drop and wind that in itself makes staying outside very unpleasant.
WHAT IS SHOWERPROOF?
We do not supply waterproof fabric. All our commercial grade are showerproof. As shown in the pictures on this page.
All the pictures indicate dry ground after a light rain shower. Even in heavy rain the water does not come directly through the shade cloth but will find it's way to the lowest point and run off, because shade cloth is permeable there will be some drips as shown in the is picture.