07:23AM | 03/04/04
Member Since: 03/03/04
1 lifetime posts
I want to add an addition and wrap around porch. I need to pour a foundation, (for addition) and slab for the porch. My problem is elevation. I will need to pour concrete against the existing structure above the top of existing concrete, mostly for the porch. The top of the new concrete would have to be a max of about 5-6 inches above existing concrete, butted against wood sheathing. The porch is to be about 6 ft wide and covered. The concrete would have a slight slope away from house. How do I prepare the sheathing for the concrete pour against it? My thoughts on this are to flash under siding with 30# felt & galv metal lapped down over and sealed to the foundation with roofing cement with an expansion joint between new concrete and flashing. With the roof over the joint and slope on concrete, water infiltration should not be a problem. Any thoughts or resources on this?


06:35PM | 03/04/04
Member Since: 01/28/03
693 lifetime posts
It is not allowable under building codes to install concrete foundations above wood sheathing.

Foundations, by code, must be at minimum at least 8-9 inches above grade and any wood muct be at least 8-9 incheas above grade.

That said, you need to come up with some other kind of structural supports for your proposed addition and porch.

This may involve removing soil so that your porch and additon has a crawlspace with floor level under the existing foundation height or something else.

But your current proposal is completely unworkable and not legal under all known (to me) building codes.


11:03AM | 03/07/04
Member Since: 03/06/04
10 lifetime posts
there are two relatively simple solutions. A) leave a 1 inch air gap between the side of the new footing and the existing porch sheathing. You would need to go to your city/county building department to find out what the minimum gap would be (and if this type of solution is possible).

b) raise the top of the porch footing so that it is at the same height as the new footing. This would entail temporary support of the porch roof, remove the lower 12 inches or so of the porch wall, pour a new cap on the exising porch footing and rebuilding the porch wall..
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