If you want the decking surface to be level the sleepers will need to be tapered to compensate for the slope in the roof deck.
Sleepers roof deck.
Water must be able to flow through and away from the deck.
It s best to be able to clean it out often.
This will provide the surface for you to attach the decking.
You can use 2x material laid flat or 4x material also as sleepers.
It s a wash as the deck keeps the sun off the roof which is good but it also stores a lot of debris in under there.
It s best to build the wooden deck in removable sections for cleaning and maintenance of the rubber roof and repair of the membrane if ever needed.
1 4 6 4 mm minimum gap where the decking meets a solid wall maximum of 3 8 9 5 mm recommended.
A sleeper system is a substructure between a solid surface and trex decking.
The decking sits on 2x sleepers usually laid flat.
Sleepers are placed between the deck surface and the ground or slab below it.
Attach the decking with screws so it can be removed later for inspection or.
Decking laid directly over packed soil will rot quickly and wood laid over concrete rots as well when moisture is trapped between the two materials.
Deck must be designed to ensure that proper drainage and air flow are maintained.
For repairs and removal of debris joist system access may be necessary.
This is the standard gapping for duralife products.
You can do a floating deck and is really your only option.
Then you will install sleepers or flat 2x6s laid flat every 16 on top of the roof surface.
Drainage access and airflow are critical.
I d put down strips of rubber roof under the sleepers.
You could glue the strips tongue sleepers or just make them a bit wider and rely on pressure to keep them in place.
A set of sleepers supports the decking and allows moisture and air to flow below it.
A properly constructed epdm roof should last 40 or more years.
To protect the roofing membrane set the sleepers on strips of epdm or rooftop walkway matting available from commercial roofing suppliers.
Trex recommendations when using with a sleeper system.
Rooftop decking attaches to treated wood sleepers separated from the roofing by strips of epdm.
Roof top deck with sleeper system install guide.
Next you will need to install a watertight epmd rubber membrane over the top of the roof deck for protection against water infiltration in place of roofing materials.