The architect for this remodel designed a deck above existing living space with no slope - zero! The deck is currently covered with billboard tarps, but this is not a viable long-term solution. The framers placed the 12" TJIs on the existing wall top plates, covered it all with OSB flooring (just as the plans called for) and called themselves done. (They weren't supposed to rip off the hip roof.)

Options seem to be:

1) convert the deck to conditioned space such as a sunroom or greenhouse:

This would require additional design and structural approvals at a minimum. Would an EDPM covering on the flat floor keep water (from whatever source) out of the living space below?

or

2) add a floor with minimal slope on top the existing floor:

The deck is 20x20' and one concern (besides water....) is accessibility from the main house to this space. Trying to make things universal design-friendly, a slope from the door probably requires some sort of ramp on the inside of the house to get over the threshold.

Does ripping 2x stock down to varying spacer thickness and attaching these spacers every 16-24" below a new OSB floor seem reasonable? Would 1/8" per foot slope be sufficient?

Ideas appreciated!!!

i have a deck over my garage roofed with EPDM and it works great. Roofing supply companies will provide a design in tapered foam that will provide the minimum fall of quarter inch and directs runoff where you want it. You'd need to build a deck on top of the roofing, so figure that your finished height will be 9-12 inches over the OSB.

Rubber roofing is uber expensive. I had quotes of $3,400 to $9,700 for 450 SF. A part of it is the foam. In a complicated design, you can throw half of it away.The rest is limited competition resulting from the manufacturers' conditional warranty. No coverage unless you use a certified installer.

I had quotes of $3,400 to $9,700 for 450 SF.

I just laid 160 sf of 0.060" EPDM membrane on a deck with nearly no slope. Materials were $300 from the roofing supply house. Because of the roll size and container size, the materials would have done an area of at least 200 sf ( I had to buy it 10 feet wide when I really needed 8' wide). At $1.50/sf , your 450 would cost about $700. I did mine in three hours, maybe 4 hours all told. Figure a full day for 450 sf. It was ridiculously easy, even for a first-timer.

Another option might be to look at a product called DryJoist or DryJoistEZ from Wahoo Decks. They are rigid aluminum channels that lock together, creating a watertight surface and allowing the runoff to go to a gutter if you wish. The channels are 2" high and your decking surface goes over them for a total of 3" in profile height. My deck has a 20' run and I think the total drop over that distance is about 1", so profile changes a total of 4". The channels don't need the subfloor and can freespan as much as 4-8 feet, so if you are of that mind, there are additional options in stripping off the existing OSB. Cost for the DryJoistEZ was $13/sf, including crating, shipping and fasteners.

I also diyed for about $2k, of which the foam was $1k. Mine drained to four scuppers so some thought involved. The rubber itself was easy.

Talked with Wayne at Wahoo Decks today. They also make a product called AridDeck that is not structural like DryJoist. AridDeck's 1" height and 20+% lower cost make it look like a possibility for installation on top the existing subflooring.

So, which would be the better way to get the minimum slope under this AridDeck decking: tapered EPS or ripped 2x stock spaced every 24" at right angles to the slope?

Thanks for the suggestions.

I'd do the ripped stock so there is some air space in there that has a chance to dry from minor leaks.

Be careful that the ripped stock at right angles to the slope does not block the flow of water from leaks.