# Porch foundation options



## joecaption (Nov 30, 2011)

Post a picture for better replys.
An on grade slab with no footers like you have now is most likly just going to be in the way when building the new porch.

And building on top of it may not be the best option. The walls would be to close to the grade so water will just come in under them, there's no footing to support the walls or post.
For the best look and far less chance of it sagging I'd be looking at building stem walls, back filling, poring a new slab on top of it.
http://images.search.yahoo.com/imag...b=13hgfn4id&sigi=119couol6&.crumb=cpCLpHoH11V
If you did it that way later on the porch could be enclosed if you wanted to.


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## Jeeps (Apr 12, 2012)

You could remove the concrete sill under the house door. Remove the old slab and dig a footer. Pour the footer and slab with wire mesh and rebar as one pour to local building code specs. In that pour, form up a sill/step under the house door....

If the house floor is 12 in. above grade, make the slab 5 in. above grade( good to stay above heavy rain water) and pour a 7 inch tall door sill/step under the house door. It means one step down/up to get in the house which may or may not be welcomed. Just a idea. Wood deck would probaly be cheaper, but hard to insect proof as a screened in porch....

The structure you use will be determined a lot from what the local building codes require when you file for a permit. good luck.


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## hand drive (Apr 21, 2012)

take out concrete 4 x6 step and cut holes in existing slab where footers will go. Use ground contact pressure treated lumber and depending on what type of decking you use build so that once it is built the decking is an inch below underside of door threshold. looks like 2x8 lumber would work for the framing with proper footing spacing as per load support.

The other option instead of cutting in footings on existing slab is remove slab altogether and build deck the same way,it just will not have the concrete slab under it. The slab being under the new deck will help with moisture control in my opinion. Either way because deck is close to the ground have spaces between decking boards to allow air flow and avoid trapped moisture.

with this design the deck support posts will be quite short depending on depth of footer below the deck. The deck joists would require all joist hangers with this type of build, no fancy exposed under deck beams here.

After frame is built and before putting decking down, staple insect screen down to top of joists for fully enclosed insect control.


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## rhesse (Apr 12, 2012)

Thanks for the ideas!

My thought was most likely to remove the patio slab regardless.

It sounds like the stem wall would be the most solid- and involve the most work! Am I right that we'd need to:

1) excavate the entire 12' x 15' area to the depth of the footers (48" around here)

2) form and pour the footers (using vertical rebar and/or a key to lock in the foundation walls)

3) form and pour the foundation walls from the footers to a height above grade

4) backfill inside the foundation walls

5) pour the floor slab- essentially using the stem walls as forms?

What would we do along the existing foundation of the house? Would the ends of the stem walls perpendicular to the house foundation just need to be doweled into the house foundation with rebar? Also, would this leave the floor slab "floating" relative to the foundation walls? Could that cause problems?

What are the advantages/disadvantages of a stem wall foundation vs. a "monolithic pour" for the foundation slab?

Thanks again for the helpful input.


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## joecaption (Nov 30, 2011)

The new foundation and slab do not get connected.
I would use block not a pored foundation for such a small job.

I would not use a monolithic slab in you area. The footing would not get you below the frost one, and you may need more height then you can with that style slab.
http://images.search.yahoo.com/imag...b=13k6hljpu&sigi=11ap4soh1&.crumb=cpCLpHoH11V


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