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Old 09-19-2012, 02:24 PM   #1
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Storm Cellar - Poured Roof


Here's the project in a nutshell ... an 8X16 (interior) root/storm cellar built into the side of a hill. Excavation is done ... footing is poured. Construction will be standard block walls with vertical rebar every 3', wire reinforcement every other course. Going about 10 courses high, then want to pour a reinf concrete roof. Soil will be going on top of the poured roof, about a foot high.

My question is about the final course ... can I use "L-block" (also heard them called "header block") for the final course, using the outer edge of that block as the exterior form for the pour? I figured on the interior wall I'd placed well shored forms (using 2x6 & 3/4"plywood) and drop this about 2" below the L in the block ... this would give me a monolithic pour into the rebar'd cavities, with mesh placed under L-block cores I won't be filling. I'm shooting for a 6" roof using plenty of #4 bar, tied all the way down to the footing ... possibly fiber reinf concrete to be on the safe side. (I'm an over-designer.)

Hard for me to explain with words ... hopefully I'm making myself clear!

So, the question is whether that L-block is the right material for that final course. This would have the top of the slab flush w/ the final course of block, with the top edge of that L-block would be exposed. Wondering if I could seal that edge (along with the entire roof slab) or if that edge will be a weak point in the structure.

I believe the other block option would be the bond beam block ... just not sure which is correct for a poured roof.

Thanks for the assist.

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Old 09-19-2012, 04:54 PM   #2
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Storm Cellar - Poured Roof


If it was me, I would make the yop course of the block wall filled solid (bond beam) and then extend some "L" shaped rebar from the top of the wall into the slab. Then pour an 8" slab as a roof.

The FEMA suggestions fema/???.gov. has some destails and suggestions for safe cells for life safety. Your room is slightly larger than a typical tornado shelter, but the principals are the same.

Dick

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Old 09-19-2012, 08:12 PM   #3
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Storm Cellar - Poured Roof


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If it was me, I would make the yop course of the block wall filled solid (bond beam) and then extend some "L" shaped rebar from the top of the wall into the slab. Then pour an 8" slab as a roof.
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Old 09-19-2012, 08:30 PM   #4
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Storm Cellar - Poured Roof


That is close, but that is what you have to work with.

Since it is not for a living space, just use "L" shaped bars (24" on a side) to lap and connect the vertical steel with the steel in the roof slab. The wall seems to be well built, but the soil pressure will be an ongoing problem, but storms will not have an influence on the loads on the stable temperature desired inside. you should not be under building codes in most of the real world since it is detached and unoccupied.

The next question is what is going to be on the new slab with possibly a 16' span (dirt, water, people, equipment?). I assume uniform moisture is not a problem.

Dick
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Old 09-19-2012, 08:48 PM   #5
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Storm Cellar - Poured Roof


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Originally Posted by concretemasonry View Post
That is close, but that is what you have to work with.

Since it is not for a living space, just use "L" shaped bars (24" on a side) to lap and connect the vertical steel with the steel in the roof slab. The wall seems to be well built, but the soil pressure will be an ongoing problem, but storms will not have an influence on the loads on the stable temperature desired inside. you should not be under building codes in most of the real world since it is detached and unoccupied.

The next question is what is going to be on the new slab with possibly a 16' span (dirt, water, people, equipment?). I assume uniform moisture is not a problem.

Dick
Thanks Dick ... that was a pic I found online, so I'm not there on my project yet. I just don't see a need to pour concrete into a bond beam like that in the pic. Maybe I'm making this harder than it needs to be ... any harm in just using regular block & building the form around that?

Appreciate the advice. The width is only 8' ... I figured keeping it relatively narrow would be preferable with a soil load on top. Only planned load on top is about 1' soil w/ vegetation. No telling what a storm might drop there though. Will try to minimize lateral pressure w/ french drain, gravel backfill wrapped w/ geotextile. Lots of clay chert from the excavation so I definitely don't want to backfill with that. Its also a root cellar ... about half the space will get jammed with canned goods & root crops.
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Old 09-19-2012, 10:15 PM   #6
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Storm Cellar - Poured Roof


With 8" block, the low vertical load does not help as much as a higher vertical load load would.

Since you are only 10 courses high and should have good attachment to a slab for lateral strength you should be O.K.

Dick
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Old 09-20-2012, 11:02 AM   #7
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Storm Cellar - Poured Roof


Dick covered this pretty well already, but I have a simple question: Is this an addition to the existing basement or stand-alone?

As for weather-proofing, I would (and always have) install rubber glue-down roofign over the concrete roof and down the sides a foot or so, at least a few inches lower than the cold joint of the wall & roof.

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