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ajoantmug 11-17-2008 07:16 AM

rebar in footers
 
Hello,
I am not too far away from pouring a monolithic slab. 18" footers, 12" wide, with a 6" slab. 20' by 16'. I am not sure how best to place the rebar in the footers. This is for a workshop in my back yard.
I gather there should be 2 rows of rebar going around the perimeter a few inches off the bottom of the footers. should there be another set higher up? Should there be vertical rebar?
Thanks!

Termite 11-17-2008 08:46 AM

It really depends on a lot of factors. Sounds like you're doing a 12x18" grade beam footing. Is 18" deep enough frost protection for your area...Kinda shallow?

Rebar is cheap insurance in my opinion. Be sure to check with the city to see if they have any reinforcement requirements first. If it were mine I'd have bars in the top third of the footing and bars in the bottom third of the footing. In a grade beam it is common to use "stirrups" (or vertical bars) every 2 or 3 feet...If nothing else they give you something to tie the horizontal bars to.

Marvin Gardens 11-17-2008 08:49 AM

Depends on local code and mostly determined by the soil type and frost line and of course the use of the structure.

Where I am at there has to be two rows of rebar in the footer, one near the bottom and one near the top. Then there has to be rebar that is bent to go down in the footer and tied to the 2 runs in the footer and continue into the main floor. These have to be every 3 feet the length of the footer.

robertcdf 11-17-2008 09:05 AM

Quote:

Originally Posted by thekctermite (Post 186227)
It really depends on a lot of factors. Sounds like you're doing a 12x18" grade beam footing. Is 18" deep enough frost protection for your area...Kinda shallow?

Monlithic slabs are not frost protected. They move along with the heave.


I would add rebar whenever you can, it never hurts. Some in the lower 1/3 as has already been said and some in the upper 1/3rd. Add verticals as needed to hold the horizontals in place. or the other option is to somehow hang them from the forms with wire but I think thats more work than its worth sometimes.

ajoantmug 11-17-2008 01:02 PM

Thank you.
I am going to place rebar in the top 1/3 of the slab at 1' 6" on center running in both directions, like a grid.

The code for footers in Richmond, VA is 18" deep. This is what they marked on my plans as well.

I will have 4" course layer of gravel in the slab area, also with a vapor barrier.

So, then it sounds like I should have my grid turn down into the footers and run down to the bottom 1/3 rebar running around the perimeter. I guess about 5 or 6" off of the ground?

Rkeytek 11-17-2008 01:21 PM

keep 2 inches clear of the edge of the conc., lash 4 rebar in a square [::]
so it creates a grade beam than hook your vertical into that

Termite 11-17-2008 01:36 PM

Quote:

Originally Posted by robertcdf (Post 186245)
Monlithic slabs are not frost protected. They move along with the heave.

Although it applies to this 320 square foot building, I'd suggest you check IRC section R403.1.1.1 Frost protection, exception 1. It states that "freestanding accessory structures with an area of 400 square feet or less and an eave height of 10' or less" do not have to have frost protection. Larger slab on grade buildings, whether poured monolithically or not, require frost protection. All habitable structures require frost protection, regardless of size.

In my opinion, allowing any building to float on heaving soil without adequate frost protection is no way to build.

jogr 11-17-2008 01:39 PM

Be sure and ask your local building department if you need a concrete encased electrode for your electrical service in the workshop. Now would be the time to put it in.

ajoantmug 11-17-2008 05:54 PM

Be sure and ask your local building department if you need a concrete encased electrode for your electrical service in the workshop

I am not sure exactly what you mean, but the electrical service will be coming up through the slab.

Although it applies to this 320 square foot building, I'd suggest you check IRC section R403.1.1.1 Frost protection, exception 1. It states that "freestanding accessory structures with an area of 400 square feet or less and an eave height of 10' or less" do not have to have frost protection. Larger slab on grade buildings, whether poured monolithically or not, require frost protection. All habitable structures require frost protection, regardless of size.

In my opinion, allowing any building to float on heaving soil without adequate frost protection is no way to build.


I am pretty certain that where I am in Virginia the 18" below ground level is the frost protection in my area.

Thank you all for your replies!

jogr 11-17-2008 06:42 PM

I believe NEC now requires a concrete encased electrode rather than a ground rod on new construction. A concrete encased electrode is just what it sounds like. It is encased in your concrete footing and your rebar can actually serve as the electrode. You need to have a means to attach your ground wire to the rebar.

Yoiu need to talk to your local building dept to see if this is needed for your situation.

vsheetz 11-18-2008 01:20 AM

Quote:

Originally Posted by jogr (Post 186520)
I believe NEC now requires a concrete encased electrode rather than a ground rod on new construction. A concrete encased electrode is just what it sounds like. It is encased in your concrete footing and your rebar can actually serve as the electrode. You need to have a means to attach your ground wire to the rebar.

Yoiu need to talk to your local building dept to see if this is needed for your situation.

When I built my 24x30 workshop on a monolithic slab a few years ago, the building permit folks had me install a ufer ground (concrete encased electrode) consisting of a length of rebar - laid horizontal in the footer area with one end turned protruding through the sill.

jogr 11-18-2008 09:11 AM

Yep, It's a lot easier and cheaper than driving copper ground rods. It's just that you have to remember to do it at the footing stage.


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