Enclosing a covered patio

Hello.

I have a completely roofed(permitted, hurricane proofed, ready to go) patio that I am going to build an addition under. The existing patio is I'd say 2 inches below the rest of the slab that the house is built on and I need to level that up. I will eventually be continuing the wooden flooring I have begun in the rest of the house seamlessly out into that addition. Rather than completely demolishing the existing patio(it has footings for the posts/beams which support the roofing structures(open beam) and rather than pouring a questionable 1-2" thin slab on top, I was going to build a sleeper floor using 2x(whatever necessary) with plywood top to make it level. I was also thinking of filling the space between the sleeper beams with rigid foam blocks of some type? Then frame my walls on top of that. I would ensure I leveled the sleeper using shims under the sleeper beams and ensure that I had sleepers wide enough directly under any place I had a bottom plate for my wall frames. The entire house is an older single wall redwood with open support beams and the covered patio is the same, so the new double wall portions I am building do not need actual structural support, they are only framing for windows/doors etc.

This is all in Hawaii climate where it is 60-85 year round where I live.

Does anyone have any thoughts on this or input on this approach?

Thanks!

Always easier to see possible issues with some pictures.
Biggest issue I've seen when people try and do this is how close the slab is to grade.
Water getting in under the wall, and splash back rotting out the siding.

Thanks. I'll post some pictures later.

Right now the patios is about 4 inches from grade(same as home slab) and about 2 inches at the sloped end away from the house.

I should note that this patio doesn't ever get wet, even in heavy rain(here in Hawaii) because the yard has really good drainage and is under a pretty healthy 2 foot overhang all around.

If you thought water would be a problem would you opt to level up using concrete or self levelling compound of some kind? Could a sleeper be built out of material no susceptible to water? (Plastics or foam of some kind?)

The slab in the house has a vapour barrier under it so water will not wick up and the the house should have a perimiter drain to take water away from the house The foundation usually shows above ground about 6 to 8 inches, this allows water to wick out and stop the splash up that Joe mentioned. Most times you also think about frost but I guess you won't worry about that.

I would trench around the outside, maybe 12" deep and install a perferated solid pipe connect that to the house perimiter drain, cover that with fabric and back fill with crushed rock.
We have here a peal stick product here that you put down with a primer on concrete. We use it to waterproof when we put a room under the garage. It come 36" wide. if you can get it that is what I would do on top of the slab but I would not poke holes in it just lay the sleepers in place. A few 2x2s screwed acroos the tops of the sleepers will hold them in place while you have the spay foam installed.
I would install the peel and stick first and then build the walls, if you it in that order, remmember you want to double plate the bottom because of the raised floor.

No. These homes are single wall redwood with no insulation of any kind. They have horizontal louver style windows with no weather treatment whatsoever. They have no conditioned spaces. The weather/humidity outside is the weather/humidity inside, all the time, instantly. They are on solid slabs that is at most 4 or 5 inches above grade. They have no perimeter drain and they have no vapor barriers. I don't see how any of this applies when the home itself is fine and has no moisture/water issues in 50 years.

Any new addition or "use change" from a patio to living space most likely requires a permit, just as you got one for the patio roof. Liability of damage from the new walls, moisture through the existing slab, all connections required--- to keep what you construct in place due to the "high winds and seismic" areas of the Islands; http://ags.hawaii.gov/wp-content/uploads/2012/10/State-Residential-Code.pdf

What design for the floor system is on your plans submitted or are you only in the planning stage now?

Gary
PS. Welcome to the forums!