Upgrading footing-less slab foundation
This is my first post on these amazing forums and I’m awed at the amount of collective knowledge here. I’m starting an extensive remodel of an old house in central California. The house was built in sections and is at least 70 years old. It is sitting on a 4″ thick slab that has no perimeter footing. In order to support a new roof, the city planner has recommended that I dig under the slab, pour a footing and tie it in with epoxied anchor bolts. That seems pretty straightforward to me. The problem is that the slab is sitting about an inch under grade. I don’t know if it has just settled over the years or what, but there is currently dirt touching wood all around the house. The new codes specify 6″ of space between the earth and the bottom of the sill. Currently that space is -1″. What’s the right approach to remedy this situation? Thanks y’all!
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shovel
Ah, I see. Thanks brownbagg, very insightful. Apparently my question was too stupid. Is this a professionals only forum or something?
no, not just pro.
no, its not a pro site, we welcome anybody and everybody. and no there is no stupid question. none at all. I just gave you one way thats all.
Well, I see two options: lower the dirt or raise the house.
If you are real lucky, your house is sited so that you could remove enough soil to get the grade down, but now wind up with your house sitting in a pond when it rains.
Raising your house wouldn't be pretty. Could be done, but bound to be expensive. It could be jacked up and set on a row of CMU.
Thanks Marson. Boy, with those options maybe it's easier just to break up the existing foundation and repour. I'm tearing down a significant portion of the house already, so it might not be too terrible to just go all the way down. Well, thanks again. I appreciate the advice!
Brownbags facetious remarks aside, you don't want to just reduce the height of grade around the house, you want to maintain a slope away from the foundation to keep surface water away.
Given that the wood siding has been in contact with the ground for some time, there is a fair chance that the exterior wall framing may have some rot in it, and now would be a good time to check.
Once the perimeter has been excavated and the new footing poured (I'd pour it so that the outside of the footing was flush with the outside of the slab), I would then remove the siding and sheathing to 8"above grade, and make any necessary repairs to the sills and studs. Re-sheath with pt. plywood right down over the footing and cover with a membrane before parging.
Well, what you may need is a City opinion on an A, B, C scenario.
A would be the simple one, you undermine portions of the existing slab and install a footing.
B would be where some rot in the mudsills was found, and coping with that
C would be if extensive rot behind the siding exists.
Why three scenarios? Because I'll wager that, at certain point of replace versus repair, you wind up saddled with having to meet current seismic rules, and not just fix it to "good enough."
Uhm, how were you to drill the 4" slab for those epoxied bolts? From above or from below? (Below would seem like a humongous bear, even if you have to excavate for an 18"x24" seismic footer.)
What sort of side yard access are you looking at? If skid-steer "wide" (or even walk-behind "wide") that wil lhelp in getting the grades right. Be aware that getting the grades right might require extensive rgrading around the house, too. Have you thought about wher you might want some raised beds for all the fill you might be cutting out?
Also, if you are going to be held to 6" clear, that will be tough sledding with only 4" of slab to work with.
What you might want to do is to find a local structural engineer to come have a look at this. If you have not run into one, ask your friends who have remodeled, or yellow pages under residential remodeling, and ask those outfits if they have a trusted engineer to recommend.
It might be that your site/house might be simpler to crib up one wall at a time, and cut in a new, to-code, seismic beam, tnen rebuild mudsills up to the first floor to code while you are at it (this may be especially true if there is extensive rot behind the siding).
An engineer with remodeling experience will have been through the hoops you may have to leap through already, saving you some grief along the way.
Thanks for the great feedback folks! I've discovered rot in the siding and in a few studs. My remodel will be very extensive, so I will probably need to upgrade the house to meet code violations. I have about eight feet of room on one side of the house and 2 feet on the other side. I'm getting the feeling from what y'all are saying that this is complicated enough, and important enough, that doing it myself is probably not the best idea. I will try to consult an engineer or very experienced contractor.I guess I'm just curious at this point about what to do once the footings are in place about that 6 inches between dirt and the frame. Do I just install impermeable vapor barrier and some sort of non-wood sheathing?
what to do once the footings are in place about that 6 inches between dirt and the frame. Do I just install impermeable vapor barrier and some sort of non-wood sheathing?
Well, if the dirt cannot be lowered, then one answer could be to have the approved footing poured with a brick or masonry ledge, and install a "compliant" surface to some convenient height, and bring the repaired siding down to that new surface approriately.
The issue with that height above ground is to get seperation of the framing so that water standing on the lawn cannot seep in, also, having that seperation makes it easier to detect if termites are trying to tunnel up to the framing too.
When you start talking to someone with local experience with this, you will get answers to many questions. Likely you will get answeres to questions not yet asked, too.Occupational hazard of my occupation not being around (sorry Bubba)