elevated concrete deck

[oregonbuilder]

I am framing a elevated deck that will be covered with 4 inch exposed agg. concrete. I was told that concrete weighs 4000 lbs per cubic yard. I think that I did the math right making a 4 inch slab about 50 lbs per square foot. if I am spanning ten feet what size joist would you use and on what centers? I am planning on a 3/4 inch pressure treated sub-floor under the concrete. Any math people that could check my math would be great.

[Allan Edwards]

Re: elevated concrete deck

Your math is correct. Can you use lightweight concrete? Obvious question is for an elevated deck where people will congregate, seems you would have liability that could reach to a criminal level. Please use an engineer to design this.

I would think this would require a steel structure rather than wood.

[David Meiland]

Re: elevated concrete deck

Hopefully you're not planning on pouring concrete directly on a PT plywood deck. Seems like waterproofing would be necessary. I did a raised patio with mortar and flagstone paving over. The whole thing got a PVC flat-roof detail before the mortar went down.

[MarkMc]

Re: elevated concrete deck

If your other dimension is greater than about 2.5' you need an engineer. If this is higher than 1' above grade you'll want an engineer. You've not given enough details to work with, and even if there were, I can think of almost no good reasons to try and do what you are attempting when there are far better choices most likely handily within reach and possibly even less expensive.

[dave_k]

Re: elevated concrete deck

i would call up someone like Hambro. http://www.hambro-floors.ws/www/v4/ehambro.nsf I believe if you give them the drawings of what you want they will engineer a system to local codes and ship it out to you. The system includes joists and decking. Hambro may not service your area but someone must be offering this service.

[Unforgiven]

Re: elevated concrete deck

That's a 50# dead load form the concrete alone, plus your deck, and the LL. The math isn't hard, but it's so much better to be able to point to your engineers stamp if something goes wrong.

I would think that if you are going to pour concrete in it you should consider corrugated metal deck pan. Oh, and any concrete at or above the 4,000 psi mark is effectively "waterproof". In this application I would probably want 4,000 PSI pump-mix, and probably with fiber in lieu of steel.

[James Eggert]

Re: elevated concrete deck

Unforgiven?
I was always under rule that 5000 was waterproof???

[larryh]

Re: elevated concrete deck

we've done these a few times, but of course it is always engineered.
pouring over wood framing is fine, just make sure you do an excellent job with the flashing and waterproofing, it's all in the details..
Waterproof concrete?? that's crazy. even if 5000 psi concrete is waterproof it won't be waterproof at the edges and where it cracks, and it will crack.
4 inches is pretty thick. The thickest we've done is 3", and we had to go with lightweight concrete on that job. iirc lightweight is 1/3 the weight?? your engineer will know...
some people around here are starting to use corrugated metal decking..i haven't had the opportunity yet, but i guess the math works out and it seems like a great way to go.

[eightinchnails]

Re: elevated concrete deck

I did a concrete deck over a 2 car garage last summer. It had a steel I beam down the center with 2X framing. The speced 3/4 ply, waterproof membrane and then 4" of concrete. Don't use the ply. go steel decking and save yourself many many issues. Oh and I would want it engineered way to risky to wing it. I am in Portland -- Oregon builder and if you would like to see the project would be more than willing to show it to you.

[DWeckler]

Re: elevated concrete deck

Have it engineered, there is no need for any wood supports. Form the slab with shoring, tie the rebar, wait 30 days and strip it. Have done this many times, some slabs up to 30' x 70' and 12" thick.Around here you can rent the shoring from aluma systems. Here are some pics of a flight of stairs I did a few years ago. 28 tons

[DWeckler]

Re: elevated concrete deck

A few more. Before you comment on the dome not being a ellipse like the stairs,the answers are that my bid was to high for framing the house and that apparently you cannot translate ellipse into Spanish.

[DWeckler]

Re: elevated concrete deck

Have a few here somewhere of a 100 ton residential deck. Might have to scan them first.

[DWeckler]

Re: elevated concrete deck

Here are two of the forms. they are covered in AZEK. The plan was to pour white concrete and have that me the finish. It came out as smooth as glass.They threw the AZEK away $$$.

[dave_k]

Re: elevated concrete deck

Nice stairs buddy. I would be really be proud of them. Were they cip or pre cast? I used to build a lot of concrete stairs. I've built a lot of curved stairs, some really huge ones. I've never built a spiral set without having concrete walls to set the stringers to. I can kind of guess how I would tackle a job like this but I'd like to know how you did it. Do you have any pictures of the formwork?

[DWeckler]

Re: elevated concrete deck

2 more. Anyone interested.