Lower than the purlin along the house 12 x 1 4 3.
Rubber roof under deck.
We all know the different types of roofing material asphalt wood metal etc but there s one type of roofing material that s just a bit different than the rest.
Rooftop deck flooring is specially designed to not puncture or tear the waterproof membrane of a flat top roof.
Incorporate the actual support blocks into the roofing system then build the deck from your support blocks.
Therefore allowing drainage under the deck.
Deck over rubber roof.
Install the purlin along the house and the outer purlin.
There is not much you can do about the slope of the roof surface.
Dexedry rubber flanges fit into flanges grooved into the edges of decking boards.
Basicly making the support areas penetrations consult or hire roofer for this part.
First mark all the purlin locations on the deck joists.
That means water will pool somewhere over such a large surface.
Then stretch a string between them.
Although it s a waterproof roofing material it has an extra quality.
Most modern flat top roofs are sealed with a single ply rubber membrane that is meant to protect the roof from leaks and water damage.
Without any slope you are going to have to entirely rely on the integrity of the epdm to protect your roof.
There are several commercially available under deck drainage systems including some that can be retrofit to an existing deck but on new decks i prefer to fabricate my own system using an epdm synthetic rubber roofing membrane and standard aluminum gutter parts.
If the span under your deck is 12 ft for example the purlin at the outer end of the deck should be 3 in.
Dexedry flanges are designed to act as spacers between boards and also as mini gutters to channel water toward deck edges.