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Discussion Starter #1
I am planning to build a concrete studio that will be built into the side of a hill on two sides. I want the roof to be flat so it can also be used as a patio. It will be a small studio, maybe twelve feet by twenty feet. The walls will be six inches thick. I can't find any information on how far I can span with concrete for the ceiling, what the rebar layout should look like or if I have to design concrete headers into the ceiling slab. Any ideas?
 

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Which sides will support backfill? Will any portion of the roof be filled/backfilled over? What kind of dirt will it be built in (sand, clay, loam, silt, etc)? What is the climate like there? I've built a lot of underground vaults in a wide variety of sizes. Give me some more detail and I can provide you some practical ideas.
 

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Discussion Starter #3
PipeGuy:
The hill faces north and is dirt/sandyclay. Our house sits on top of a low hill. This is a mile from the beach in Northern California, in Eureka. Not much frost etc, not much snow to speak of but it does get wet in the winter. It is usually 55-60 all year round. The north side wall will support backfill and a portion of the west wall. The ceiling will not have any backfill. I have poured foundations, slabs and retaining walls but I don't have any clue on how to make the ceiling safe. I was going to use those new foam blocks for sidewall forms. Thanks for any info.
 

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calypso said:
I don't have any clue on how to make the ceiling safe.
Forming, pouring and stripping a concrete deck (roof) is a very dangerous task - even when done properly. A 20 x 12 x 8" thick reinforced roof slab weighs about 26,000 pounds. If not properly formed it will collapse with potentially catastrophic results. If stripped prematurely it will collapse with potentially catastrophic results. The ceiling can't be safe without safe walls and safe walls require a suitable slab (footing).

I've never designed a concrete structure. I've reviewed hundreds of previously approved designs for underground sewer structures. All of them incorporate substantial amounts of rebar in the slab, walls and roofs. If I were building something like you're describing it would probably require 30+ yards of ready-mix and about 5700# of rebar. If you want to correspond by e-mail about specific design specifications I've exprienced feel free to contact me.

I've seen hollow core polystyrene blocks systems. I have no idea to what extent they can accomodate rebar. I wouldn't build a concrete roof over walls that weren't substantially reinforced. I wouldn't backfill an unreinforced wall.

Let me know if you want more info.
 

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Discussion Starter #5
I knew it would take alot of rebar and proper designing but now you have me scared. I am going to think about this alittle. For this job it looks like I will need an engineer and all the proper permits. I may build a normal roof with a double ceiling, and not worry about killing myself or someone else. If you have time to e-mail me a drawing of the ceiling of one of your projects, I would be interested in looking at it. Thanks for your time PipeGuy, I appreciate it.
 

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calypso said:
now you have me scared..
Didn't mean to scare you - just let you know of the realities of forming and pouring and overhead deck. As it sounds like you already know, the slab and walls are fairly simple. The roof is simple too but the consequences of it failing can be substantially higher.
I was thinking last night that there might be earthquake building code requirements for reinforced concrete in your locale that you'd want to take into consideration. I've never seen designs that take the potential for seismic activity into account.
The drawings I have are all full sized blue prints. If I have the time this month I'll get a couple reduced and e-mail them to you. With the holiday noise now turned up to "11" I'm just not sure that it'll happen by year's end.
 

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Discussion Starter #7
That is a good point about the earthquakes. We just had a small one a few days ago. I'll have an engineer draw me up plans for the ceiling if I go that route. You can wait on the plans. When I get to that phase, I'll give you a hollar. Thanks for the info.
 
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