Capping a small foundation

[digger2]

This is for some of you more expert "concrete" kind of guys.

What i'm doing is,this summer,i'm building a root cellar off my basement wall.This means digging a hole next to the foundation of my house,pouring footers,laying up blocks to just above ground level,then "capping" the top with concrete.The reason for the concrete cap is,not just to close the top off,but it will double as the floor of a very small front porch with a roof on top
to protect it from the suns heat in the summer.I also plan on insulating the "CAP" underneath to help keep the heat from the sun out and help keep the cool in.Not the ultimate solution or location for a root cellar,but i'm thinkin of when i get older so i dont have to walk outside to who knows how far to a "traditional" root cellar.My idea was easy access.
This thing is only gonna be about 6'x10'.Not very big,but its only me and my wife.Now,the question..................
What is the best way to support the concrete while "capping" this thing?I've been told to use plywood,resting on the inside top edge of the blocks,then brace the crap out of it from underneath till it cures.I do plan on a generous amount of rebar being imbedded in the cap.And remember,its only gonna be about 6'x10'.I would like to have all the bracing removed from under the slab after its cured so its all open.I've worked with concrete before plenty,but not doing a "cap" job like this.How do the pros do it???? There will be no weight on it except for a couple of lawn chairs,with me and my wife in them,and probably a couple of beers.......thanks,Digger2


Oh,dont worry....nobody will be underneath while the pour is going on............................

 

[/pine]

It sounds to me like you are pouring a suspended slab....a "cap" would just be as wide or a little wider than the concrete block...?

Personally I would recommend getting some quotes from contractors for pre-stressed pours...

 

[varmint]

You really should build it to handle a heavier load than you, your wife, two deck chairs and maybe a dog. Say the next owners have a crowd of folks out there dancing or something?
Anyway, how about getting some sheets of corrugated metal decking, then use heavy welded wire reinforcement, held up properly with chairs, when you pour. Not difficult, once the decking is cut the right length (at supply house!). Make sure you have at least 4" min. thickness.

 

[digger2]

Yeah,i guess suspended slab would be the right terminology.And it will be at least 4" thick.Maybe 5".
Started thinking about it....i could incorporate some sort of "joists" underneath to at least help hold the weight until it cures,maybe just leave them there after it cures,although i doubt they would actually help hold the weight after the cure.I know i could come up with something as far as supporting the weight till it cures.I guess my real question is will the concrete take the stress under its own weight,to support itself,with the supports being removed after it cures.I can see cracks happening.But then my garage floor was done by a "pro" and it has cracks too.
Being the kind of guy i am,i want to do this myself,and i know it can be done.I guess i'm just open for suggestions on the proper way to do it.Oh,Varmint.....good safety suggestion about the next guy to get the place,who knows,it could be my grandson.

Digger2

 

[KennyG]

Regardless of how you do this, the concrete will require reinforcement. With reinforcement a 4 inch slab will be adequate for this as long as you are not going to drive over it. However, I would think about using a version of the decking approach used in commercial construction. If you can get some heavy gauge corregated metal to cover the ceiling, shore it up from below temporarily and pour over that, you end up with a metal ceiling left in place.

 

[Egon]

Look into a precast floor panel from the local concrete plant. Might be the easiest way to go.

 

[/pine]

Look into a precast floor panel from the local concrete plant. Might be the easiest way to go.

Very good suggestion :thumbsup:

 

[rimshot]

With some careful workmanship, your concrete free spanning deck will last for years. Look at some examples of engineered spans from concrete reinforced with stretched steel in bridges and hi rise building floors. Even the top of your septic tank spans practically 6' and is at best 3" thick.

Make sure your block walls come up plumb and level with a good footing on a compacted base dug below your local frost depth. Fill several of the block cores with concrete and 3/8 or 1/2" rod and use rod across and though the spanned pour in both directions.

I have done what you are proposing the job is entirely doable.

rimshot

 

[kutzzbill]

What I did when I built mine back in Illinois, I set the forms and rebar up beside the concrete walls. I poured it, let it set up and then I rolled it on to the building with pipes. I then sealed it with foam and let it down on the walls with hyd jacks that I had it standing on after it was in position. If you need it connected better,you can buy the redhead brand of epoxy, and glue threaded rod in to the walls and bolt the top down. This is the best way I could figure out to do this all by myself, and I drove my bulldozer over the roof to test it. It held fine.

 

[SixHoeBob]

The galvanized deck panels are a good idea. Build your forms so that the slab overhangs the foundation 1.5". Tapcon the forms to the foundation, brace the forms to prevent pushing. Build temporary 2 x 4 walls to support the galvanized decking. Put the studs on 16" centers, and build a wall every 2 feet.
Put a horizontal brace on each wall, halfway up to keep the studs from buckling.

The minimum concrete thickness should be a full 4". Use 3500 PSI concrete.
Put 1/2" re-bar on 12" centers, going in both directions, tie wired together, on chairs.

Make sure you are thorough in your preparations. Once the concrete arrives, it is to late to upgrade the forming.

I am not an engineer, therefore I err on the side over-kill.