Hello. Has anyone had a condition where there is a basement below a covered open porch? What is wanted is a 24’x24′ basement garage with a covered porch on top of it. So, I am wondering about proper water proofing on the roof/floor and the best material to construct the roof/floor out of. My first thoughts are concrete planks spanning the 24′ with a rubber membrane then a type of floating deck or maybe an adhered outdoor tile. Any advice greatly needed. Thanks.
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For a metal roof, install solid decking such as OSB or plywood.
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Do you want clear span? This is the most expensive solution.
If you can accept posts, then 4" concrete on a metal deck.
You're going to need an engineer. This is not a DYI/ wing-it project. The engineer can provide 2-3 preliminary solutions to assign cost and design priorities.
At grain may be needed. That's a lot of runoff.
For waterproofing, Laticrete has a spec for what's involved:
https://cdn.laticrete.com/~/media/product-documents/product-data-sheets/lds2900_plaza-deck-system.ashx?vs=1&d=20171212T164509Z
Frankie
Depends on how much $ you want to spend, your expectation of how long you want before repairs/maintenance issues arise and if the garage below is climate controlled. A lot of different ways it can be handled. The simplest/most affordable would be to build a wood frame flat roof (1/12 pitch) roof above the garage and install a floating deck above it or a better option a deck built above the flat roof.
If you want something that is maintenance free and will last the life of the home. I would install a hollow core slab above garage. Grout the seams of slabs as usual. A layer of geo textile fabric on that. Then a layer of EPDM. Followed by another layer of geo textile fabric. Finally, a poured slab on top of that with 1/4” per foot slope. Can apply any finish you choose over the concrete or leave as is.