Structural slab

[SiGmA_X]

Mods: if this post should go elsewhere, please move it. I figured maybe floors would be my best bet...

How would one go about guesstimating if a slab is a structural slab or a slab on grade? The question arises when discussing if it's safe to cut a hole to pour a reinforced footer for a new hoist.

Thanks for any input!

 

[larry4406]

Grade would be my first clue.

Detached garage with slab level or slightly high relative to surrounding grade, then likely slab on grade.

Attached garage with slab near first floor yet house has a basement, then likely a structural slab.

Building practices will very by region.

 

[SiGmA_X]

The house and garage is on a pretty steep hill. The first floor is a good 8' above the garage and in the crawl space it appears they mostly leveled the soil under the house, so the crawl space has equal height throughout. More or less.

I called the permit division and they have original plans on file, I know what I'm spending Friday morning doing.

If it is a structural slab, would it be possible for an engineer to design a modification to it to allow for a footer for a lift to be sunk in the middle of the slab? I assume yes - money and time fixes all?

 

[larry4406]

The house and garage is on a pretty steep hill. The first floor is a good 8' above the garage and in the crawl space it appears they mostly leveled the soil under the house, so the crawl space has equal height throughout. More or less.

I called the permit division and they have original plans on file, I know what I'm spending Friday morning doing.

If it is a structural slab, would it be possible for an engineer to design a modification to it to allow for a footer for a lift to be sunk in the middle of the slab? I assume yes - money and time fixes all?

Sounds like you have what we call in my area an "integral" type house which means the garage is integral to the basement foundation with living space above, although you have a crawl space under the adjacent living area and not a true basement is what I surmise. That said, it is sounding more like a slab on grade which would make your life easier. Picture is worth a 100 words. See example pics of what I'm thinking you have.

On a structural slab, there will be grade beams with reinforcing steel. I would assume that an engineer could design a retrofit pit/footing for a lift to work with the structural slab but I have no experience with this.

 

[SiGmA_X]

I'll get a better picture soon. What you're describing is my garage/house foundation setup. I really hope the permit/planning house plans confirm its slab on grade. I'll know Friday!

 

[larry4406]

I'll get a better picture soon. What you're describing is my garage/house foundation setup. I really hope the permit/planning house plans confirm its slab on grade. I'll know Friday!

I'm not a betting person but I'm pretty certain you are slab on grade.

Keep in mind that many jurisdictions do not keep track of slab designs. I've had many houses where due to poor soils we had to put in structural basement slabs and spread footings (24" wide vs 16") and this was all driven by 3rd party geotech inspections external to county inspections. All the county received from the 3rd party was a cert that basement slab was good.

Company I work for uses 3rd party inspections because we can demand inspection at 7 am and pour at 730. Can't do that with county inspections and when concrete pumps are involved can't afford delays.

 

[SiGmA_X]

I'm not a betting person but I'm pretty certain you are slab on grade.



Keep in mind that many jurisdictions do not keep track of slab designs. I've had many houses where due to poor soils we had to put in structural basement slabs and spread footings (24" wide vs 16") and this was all driven by 3rd party geotech inspections external to county inspections. All the county received from the 3rd party was a cert that basement slab was good.



Company I work for uses 3rd party inspections because we can demand inspection at 7 am and pour at 730. Can't do that with county inspections and when concrete pumps are involved can't afford delays.

Good info, thank you. The county thought they'd have slab plans on file but I was talking to a help desk lackey, she may have no idea at all.

In the event I can't get plans for the slab and a third party signed off and the third party doesn't have records from 16-17yrs ago, would I be safe to cut and have my hole engineered after I find rebar? I'm kind of guessing the answer here is yes.

 

[SiGmA_X]

I pulled drawings Friday. The quality is poor, both of the microfilm and of my camera action. I believe the garage slab does not have rebar, but it does have a structural cantilevered footer. See picture - sorry it is so big.

I placed a red arrow at a mark at the left end of the slab that is visible in the picture. Is this mark referring to 9" OC #4 bar in the slab? I can't imagine it is because the other bars are called out per-each, every X distance between. But I'm far from an expert and I'd like further input.

If I wanted to bury a 2" conduit in the slab, right up against the wall, would my best bet be to use a concrete saw to cut a 4" deep channel (thickness of slab) and then jackhammer it out?

Thanks for all input!