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Concrete block interior wall load on basement floor.

Concrete block interior wall load on basement floor.

Concrete block interior wall load on basement floor.


I am designing a small home fallout shelter in the basement. I am worried that building an interior concrete block wall will crack the basement floor. The wall will weight 750lb per sq ft, for a lenght of 6 feet. The entire 6 ft long wall will carry 4,500 lbs of weight on top of the existing basement floor. I do not know how thick the floor is. I am sure it is a conventional thickness, whatever that is, (4" ?).

Will this crack the floor in the future? If so, how can I design it so the basement floor will not crack?

Here are some extra details to save time from asking me questions.  The wall will abutt the existing exterior basement wall at one end of the 6' long wall, so their will be some footing support at this one end of the wall. This new 6' wall runs parallel to the exterior wall and is 4ft away from it. This is a residential one story wood structure home in Missouri where everyone has a basement. Part of this 4,200 lbs is the concrete 12" thick ceiling so that should explain the total weight. The wall will be 70" or so tall.


RE: Concrete block interior wall load on basement floor.


If the wall is only 6'why not span it from one end to the other. From what you say I'm not sure there is support at both ends though. Otherwise put a pier foundation in at the unsupported end. You can then start with an RC beam cast on the slab making sure it's suitably tied into the external wall. In addition the wall above it will do some arching of it's own to transfer the loads to the ends.

Carl Bauer

RE: Concrete block interior wall load on basement floor.

You can as well do all entirely anew by cutting the rectangular base and making a new mat foundation. Your plan is so small that very likely a mat fundation doubly reinforced nominally atop and bottom and 12 in thick as the roof will suffice. Say #3 or #4 @ 4 or 6", x and y directions, top and bottom. You have more to worry for lateral destruction than by roof or foundation.

RE: Concrete block interior wall load on basement floor.

Thank you Carl and Ishvaaag, for your replies.

Your replies both indicate that cutting into the floor for a footing will be required reqardless of the final design.  This is exactly what I needed to know. Thank you both very much!

 I am not looking forward to cutting up a perfectly good concrete floor (lol) and toteing tons of concrete upstairs. I make have to abandon this project as much as I would like to have a little home fallout protection, especially in light of the complete civil vulnerability to anykind of radiation exposure, be it accidental or an isolated terrorist event. The only shelters in existence today are those provided by-and-for high ranking government officials, and I suppose all the Beverly Hills homes are adequately protected. It is my children that I want to protect when no other protection exist.

It might be more practical for me to build an 8 x 10 foot concrete shelter annexed outside to the house somewhere. Maybe a garage extension into the backyard. That way it could relax constraints on square footage verses stealing space from the home basement. And of course I would have the bonus option of using 18 to 24" walls and ceiling instead of the minimum 12". Could you give me a ballpark figure on what such an annex would cost to have drawn up by a concrete engineer?

It would have to include spec's for a 6" ventilation openings, 2 exits for humans, a pathway for electrical and anything else that is desirable or deemed nessesary by the trade. It is not to be a blast shelter ( I can't afford the door and I doubt a terrorist will announce their intentions), but rather, only a fallout shelter.

There are tons of web sites that promote home fallout shelters, but only to market their survival products. The understated problem is that concrete shelters are not small projects for a home owner. There are plenty of free web plans outlining how to stack concrete blocks in your basement for an expedient shelter, but that is just not practical to move 4 tons of bricks within an hours notice of radioative fallout. It's not even practical to store 4 to 8 tons of blocks on my property. And the lack of good design will lead many to dangerous structures.

Years ago, in my youth, I poured monolithic sewer manholes and would do much of the shelter labor myself. But I would need a set of engineering plans and so now I am cursious what that would cost.



RE: Concrete block interior wall load on basement floor.

If you figure the volume of concrete you will have...the cost of formed, placed, reinforced, etc. concrete in-place varies but a good rough estimate is about $325/cy.  Doors, vents, stairs, etc. would of course be extra.   You can get cost data from your engineer who typically will charge you around 3% to 6% of the cost of the project that size.

Best thing:  find a local engineer who can look at your site, and provide you with a quick rough estimate of cost, size and fee.

RE: Concrete block interior wall load on basement floor.

Thanks for the reply Jae. That helps me develop the basic ballpark construction costs!


RE: Concrete block interior wall load on basement floor.

Of course a separate construction made of reinforced concrete will be safer and better.

I didn't mean what you want to do is not feasible, soil and more with a concrete slab on grade has some strength and it could -maybe- be enough to your purpose, the only thing is that architects and engineers are out duty charged with ensuring the wanted behaviour, and we must deliver constructions that not only may well meet the life safety standards, but ones that surely (to the extent mandated by the codes) will.

So our recommendations go to safe procedures that may or may not be suitable to the intent of the owner.

In any case, if there's some risk of lateral damage, concrete blocks only rarely will be the way to go.

RE: Concrete block interior wall load on basement floor.

Try pouring a new mat slab over the existing slab. The new slab can be designed to support the wall. You might lose some necessary headroom, though.

RE: Concrete block interior wall load on basement floor.

Thanks Zulak,

Your suggestion is a idea I had not thought of and I will consider it as I stew over this project design.


RE: Concrete block interior wall load on basement floor.

I'm no pro, but even if you build a fall out shelter in the basement, you only have concerate walls, and the fondation.  But if you intend is to protect your family for complete civil vulnerability to anykind of radiation exposure, be it accidental or an isolated terrorist event you really don't have that much protect overhead where radation and bio-hazards can seep in thourgh the cracks of the floor over head.  I'm not tryin to insalt your intelligence but it seems as though it would be a waste of money and effort.  But in theory it seems to be a great idea.  
If it were I, i would build the shelter underneath the basement I realize it entails a much more work and money but if shelter is what you are looking for i think that would be your best and most effect route.

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