Poured wall in existing basement?


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Old 11-18-13, 06:37 PM
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Poured wall in existing basement?

I have an unfinished basement in an existing home to which I'd like to add a weather safe-room. I've looked at FEMA recommendations, and there are a few options to choose from, but I'm specifically wondering if anyone has good ideas on how to pour a wall in an existing basement. The top three options I can think of are:
1) Use ICF blocks to build forms and pour to fill. My concern is how to mix or deliver the concrete as well as how to pour up to the existing ceiling. I can be a few inches lower because part of the concept of the saferoom is to separate the saferoom ceiling from the floor above.

2) Build a wall with mortared concrete blocks. FEMA recommends filling the block, so the problems here are the same as pouring in ICF. Possibly less concrete needed, though.

3) Use standard wood framing with plywood exterior and dry-stacked solid concrete block in-fill.

Would love other ideas/suggestions!
Thanks,
Guy
 
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Old 11-18-13, 06:55 PM
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Why not just use solid blocks?
 
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Old 11-18-13, 07:11 PM
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See, that's the kind of idea I knew was escaping me...simple. Only question, I guess I imaged that filling concrete blocked created a very strong, "interlocked" system...would a mortared solid block system be as strong and impact resistance?
 
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Old 11-20-13, 06:03 PM
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There's no way mortared blocks of any kind will perform as well as CIP, reinforced concrete. Assuming reasonable (and equal) quality of workmanship, of course. You don't mention the dimensions of your wall, but if we presume an 8' x 12' rectangular corner of your basement, using two new 8" thick walls, the volume works out to 4 C.Y. Enough to avoid a small load charge, ready-mix concrete is the only way to go.

Getting the mud into the forms can be accomplished by renting a ground concrete pump (meaning it's just a trailer with a hopper and pump mechanism, pulled by a pickup truck, with the concrete hose resting on the ground). Last time I used one, the rate was $400 for a 4-hour job, with operator. You can snake the hose through a basement window and into the top gap of your wall forms. Building the forms stoutly enough will enable you to vigorously beat on them to adequately consolidate the concrete.
 
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Old 11-21-13, 03:50 AM
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Bridge, I would question whether or not the slab would handle the pour, being vertical and all that weight. Would it not benefit to cut the slab and make a footing pour of, say 12" x 12" for the course? Just curious. I know the OP was just questioning the best construction method, but I wanted to interject that.
 
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Old 11-21-13, 04:37 AM
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Good point Chandler --- that should also be the case for the block wall method.
 
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Old 11-21-13, 08:34 AM
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Crunching the numbers, and assuming normal weight concrete (150 Lb./C.F.), a wall 8" thick and 8' tall will place an additional stress on the slab beneath it of less than 9 PSI. Feel free to check the arithmetic if you don't believe me: (8' x 0.6667' x 1' x 150) / (12" x 8") = 8.33 PSI. Adding a bit more than 8 PSI to a slab that's designed and constructed to resist somewhere around 3000 PSI shouldn't cause much of a problem.

All bets are off, of course, if the slab has any settlement voids under it, as the slab concrete may then crack and deflect. If voids are present (easily detected by sounding with a hammer), cutting open and removing the slab in the wall's footprint and pouring a contiguous footing with it, directly on existing base material that has first been re-compacted, would be the way to go.
 
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Old 11-21-13, 07:57 PM
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Thanks all for the replies...I had wondered about the potential need for a footing with either a poured or block wall. This is a corner of the basement with two existing walls. I'd want the finished room to be approximately 6'x10', with a door in the 6' end. It is a relatively new construction home with (I believe) a 4" slab with closed-cell spray foam under it. There is in-floor radiant heating run in most of the slab, but not this area...there is, however, plumbing that runs under the slab (and under the spray foam) in this corner.

Bridge, I was assuming that a poured wall would have to be stronger than a mortared one (how could it not be), but I suppose the question is what's strong "enough" (don't know until the tornado hits, do you). I believe any of the options will improve my families safety. With the hopes of controlling costs, I'll probably have to balance what I can do myself vs what the benefits are of hiring out. I'm starting to be partial to the plywood sheated, wood framed wall with loose CMU in-fill because it does seem very DIY-friendly. The other consideration is that when we are not hiding from a storm, I'd like to use this room for wine storage...so there would be some benefits to insulating the room to help keep it cool.

Would love to hear any other thoughts or ideas! Just in case anyone else is interested in a similar project, here is FEMA's site with a LOT of free detail on safe rooms:
FEMA P-320 - Taking Shelter From the Storm: Building a Safe Room For Your Home or Small Business | FEMA.gov
 
 

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