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Old detached garage stucco and slab below grade

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Old 11-15-20, 03:43 PM
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Old detached garage stucco and slab below grade

Hi All! Thanks for any help in advanced. We recently moved to a new home near Oakland, California. The property has a detached garage in the rear corner that I intend to use as a workshop (mostly woodworking). The house was built in 1914 and I imagine the garage is also quite old. The structure has stucco over the original redwood siding and is built on a 5 inch thick slab that is currently ~18inches below grade on 3 sides. One side is a planter bed that has been actively watered for many years and as you can imagine there was significant damage to both the wood members inside and the stucco outside. I have since replaced the sills and reframed as necessary. I also have bids from plaster subs to tear out the bottom few feet of stucco, tie in nwe building paper, and restucco with a weep screed installed (structure currently has stucco down directly to the slab foundation as was typical).

What I am not clear on is how to proceed with the grading on the outside of the structure. I am in a unique scenario as the garage is right on the lot line, and as such my ability to modify the grade is limited.

I recognize that the “correct” solution might be complicated and that there is no easy fix for this. I am trying to toe the line between keeping it in scope/budget, but also something that has a shot at lasting. We bought this house with the intention of being here for a long time.

I have documented the current topography and my current thought for a solution here (I also attached a PDF for those who cant access Google Docs):

I also have a bunch of photos showing the situation here
 
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Old 11-16-20, 10:46 AM
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A few additional thoughts:

1) I just realized that if I put a retaining wall along the back of the garage I will need a drain on the backside of the wall, facing my neighbors house, wont I? I was thinking I could just have a french drain along my foundation, but after some more reading it seems clear i need drainage on the side of the wall doing the retaining.
2) With the above in mind would it be a bad idea to not have a retaining wall at all and just fill the trench with gravel wrapped in geo fabric?
3) My next thought was to use elastomeric paint on the section of stucco that will be below grade to help with waterproofing a bit. I can also have a couple vents into the wall cavity on the inside of the garage to promote airflow.
 
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Old 11-16-20, 12:24 PM
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I saw your retaining walls and drainage but that looks like a lot of work to build, will take up a fair bit of space and will create an odd, narrow trench around the building that want's to collect with leaves & twigs. I would consider cutting the wood & stucco portion of your garage's walls off above grade and build/pour masonry walls for the below grade areas. You can install a perimeter drain around the outside and damp proof the footer walls for increased water protection inside the garage.

 
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Old 11-16-20, 12:36 PM
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I saw your retaining walls and drainage but that looks like a lot of work to build, will take up a fair bit of space and will create an odd, narrow trench around the building that want's to collect with leaves & twigs. I would consider cutting the wood & stucco portion of your garage's walls off above grade and build/pour masonry walls for the below grade areas. You can install a perimeter drain around the outside and damp proof the footer walls for increased water protection inside the garage.
Hey Dane, thanks for your reply. Agree on your concerns with the trench. Part of me wonders if I can skip the retaining wall and just fill the trench with gravel wrapped in geo fabric?

Adding a curb is an interesting idea and from what I can gather, the right way to do it. A few questions/concerns:
1) These walls would need be at least 24" high
2) I worry about that additional mass on 50+ year old slab that is only 5 inches with no footings
 

Last edited by OldHouseTimV; 11-16-20 at 01:17 PM. Reason: added quote I am replying to for clarity
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Old 11-16-20, 02:27 PM
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Without a footing, what prevents the slab from migrating toward the drainage trench over time?
 
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Old 11-16-20, 02:30 PM
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I once had a cottage where the narrow side yard sloped down towards a carport that was enclosed and made into living space. I excavated the area so the bottom of the dig sloped away from the house. I put a perforated drain pipe in the low area and it drained to daylight. Then I backfilled the area with clean crushed stone. So, on the surface you see stone sloping toward the house but any water quickly filtered through the stone to be directed away.

As for adding masonry walls for the bottom two feet it's not much different than you have now. Those load bearing walls are still bearing in the same place. The only difference is the bottom couple feet is no cement blocks instead of wood framing and stucco. Still, you are correct that it's not good to have all this resting on a slab with no footer.
 
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Old 11-16-20, 02:35 PM
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Without a footing, what prevents the slab from migrating toward the drainage trench over time?
I'm not an expert (hence why im posting haha) but my understanding is that is the intent of a floating slab, to migrate as the soil moves to prevent cracking. Having gravel around the outside (instead of dirt) doesn't seem too different than simply having the slab above grade to start, right?
 
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Old 11-16-20, 02:44 PM
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I once had a cottage where the narrow side yard sloped down towards a carport that was enclosed and made into living space. I excavated the area so the bottom of the dig sloped away from the house. I put a perforated drain pipe in the low area and it drained to daylight. Then I backfilled the area with clean crushed stone. So, on the surface you see stone sloping toward the house but any water quickly filtered through the stone to be directed away.
This is kind of what I'm leaning towards right now. Trench, put in a french drain (to a dry well though, as I have no way to get it to daylight). I can have the bottom of the trench slope away from the building and then backfill with clean crushed stone up to grade level. I could cover the below grade sheathing with foundation waterproof membrane, and put an elastomeric coating on the below grade stucco. Then put an interior vent into the cavity to encourage some airflow.

If I do this should I still have a weep put in seeing as though it would be covered by the crushed stone? The alternative would be to follow the old school method and stucco down directly to foundation, though I guess I gravel covered weep can't be worse than no weep at all.




As for adding masonry walls for the bottom two feet it's not much different than you have now. Those load bearing walls are still bearing in the same place. The only difference is the bottom couple feet is no cement blocks instead of wood framing and stucco. Still, you are correct that it's not good to have all this resting on a slab with no footer.
Understood. This feels like a larger project than I was hoping to take on. A french drain and trenching is a pain but something I'm comfortable implementing. Anchoring a new curb to the slab will be a lot more research and material/tools to procure
 

Last edited by OldHouseTimV; 11-16-20 at 03:08 PM. Reason: attached an image of the proposed trench and backfill with gravel
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