Under contract on house-concrete slab/plumbing advice needed asap
My spouse and I are currently under contract on a house that has a separate garage. The garage is on a concrete slab that was poured in 2018 and is already showing a decent amount of settling/cracking. The house is located in San Antonio, TX which apparently is known for foundation issues and settling due to the clay soil and flooding. Us following through on the purchase of this home is dependent on the plan to renovate this separate garage into a rentable short term airbnb unit. We have budgeted $30k to complete the garage into airbnb renovation. My question is 3 fold:
1. In my research it appears that slabjacking (polyurethane injection) looks like the most effective means of repairing the slab while also giving decent protection against further settling. Does anyone have any experience or opinions on this idea?
2. The garage has electricity but no water so we would need to run plumbing and sewer to the garage for a small kitchen and bathroom. Does anyone have experience running plumbing through an existing concrete slab? General idea of how expensive or difficult this is?
3. Would it be best to run the plumbing and then slabjack the slab? Or should we repair the slab first and then run the plumbing?
Any opinions/advice are greatly appreciated!
Replies
A. Slab jacking is not a permanent solution when soil has a lot of clay. Clay is incredible stuff. Very sensitive/ reactive to pressure when wet. If it's not a clay issue, jack it.
B. You'll have to run all drains to a sump pump in an ejector pit which will be below the slab. From there you'll have a drain pipe to street and a vent pipe to roof.
https://www.libertypumps.com/Product/Pro380-Series
C. Find out how water is getting to the affected area and divert the water to a dry well. Clay is only spongy when it's wet.
D. Might be a good idea to contact an engineer to specify the repair of the slab if it's going to be used as a habitable space. Engineer might tell you to cut out the sinking section and create a bridge of concrete over the spongy soil.
E. Repair and plumbing install will happen in tandem. Mark out. Excavate. Install. Repair.
I've never done it but slab jacking seems terribly expensive. Are you sure the slab is settling and not just cracked? If it is settling are the footings also settling? All concrete slabs will crack. Here in the west the trend is to use post tensioned garage slabs (Note these cannot be cut). Is the slab level or is it pitched towards the door? If it is level check to see how flat it is with string lines. If it is flat, don't worry too much, just plan on dealing with it when you install floor covering. If it is pitched you are going to have to level it out.
To convert your garage to an AirBnB with today's cost of materials, I would imagine that $30K is an insufficient amount of money...
If you go with a sewage ejection sump and pump, you will need to cut the concrete slab, and dig trenches for the drains from the bathroom and kitchen. Also, if the water table is high, a sewage ejection pump may not be the best solution. The benefit will be that if your slab has indeed settled and not just cracked, the digging of trenches will provide access to the base material under the slab.
I just completed a basement "spa" for a customer that consists of a sauna and a 3-piece bathroom, and initially I was planning to use a sewage ejection pump, but the water table level made me rethink that option. Instead I used one Saniflo macerating pump for the toilet (~$1,200 with toilet) and sink, and a Saniflo gray water pump (~$320) for the shower to pump the waste water up to the level of the main sewage drain. This worked very well, but the shower does need to be elevated so the shower drain has a 1/4" per foot slope. (To minimize this step height for a senior couple, I cut a small hole in the concrete slab that houses the shower drain trap.)
I would hope that, since the garage slab was poured in 2018, that there is just some cracking, and not significant settling. I would ask the owner what was used as a base beneath the slab, the slab thickness, and what reinforcing was used in the slab pour...
I second this opinion. I almost fell out of my chair when I saw 30k. I would try to get some commitments to hard prices to see if you are even in the ballpark there. With material costs the way they are, my bids expire in one week, so if you have old bids you need to follow up and make sure they will still honor those. I get that Chicago is a different market, but around here 30k buys you a kitchen (modestly), not a full air b&b garage conversion. Not trying to rain on your parade, just trying to make sure you’re not setting yourself up for disappointment....
I'm going to guess that the $30K number came from homeadvisor.com, which shows very misleading and confusing numbers that are probably off by at least 3x to 5x, and maybe more, with today's material costs. If you read the info on their website, it talks about $30K being, on average, the high end of the cost! Then it talks about additional costs for a bathroom for $3K-$25K and a kitchen for $6K-$50K, plus cost of appliances. This is not very helpful for someone looking to budget for a garage conversion!!!
As recommended by user-6785380, get some bids, and you'll be surprised by the cost vs. the $30K assumption for the garage conversion. Just the mechanicals (plumbing; electric; HVAC) will exceed the $30K budget, I would expect.
1. I second the Saniflo recommendation! Three years ago we built & finished a cabin shell for my dad to live in on our property, and we went with the Saniflo system. It's worked very, very well for him and we're all happy with it. The one we bought has inputs for the sink and shower as well--all the plumbing goes into the Saniflo box and from there into our wastewater line--and, touch wood, we haven't had a single problem with it.
2. I'm going to disagree, actually, re budget. I don't think $30k is such a ridiculously small budget, given that we don't know exactly what needs to be done to it, how much the OP already has wrt materials and such or how much OP plans to DIY, etc. I'm currently planning a Quonset hut storage/ADU in my backyard, and expect I'll be able to finish it for under $15k, given the amount of work I plan to do myself and the quantity of materials I either already have, will be able to get free, or will be able to get at a large discount. I'm currently contemplating running it off solar and building that set-up myself, with professional help for only a few parts of it, as well as digging the trench for the plumbing and installing most of the plumbing myself (I'm about to replace the sink & faucet in our master with new ones [including self-built vanity] and then tear out the fiberglass shower & build a new tiled Kerdi shower, so by the time it's time to start finishing the hut/plumbing it, I'll have done it once before already).
I know it was three years ago and believe me, I am well aware of the skyrocketing cost of materials (I have a woodworking business and it's killing me!), but we finished my dad's cabin, including having all electrical and plumbing installed professionally and hiring help for some things we'd now do ourselves, with pretty high-end materials, for about $18k. If the OP is planning on even doing only as much DIY as we did then, $30k isn't wholly unrealistic. (Or maybe OP has time to wait for costs to drop back down a bit.)
Again, I'm not saying y'all are wrong, or even wrong to advise double-checking those costs. I'm just saying there's not enough info to say with certainty that $30k is unrealistic. It might be. It might not be.
JMO.
You can use a wall hung toilet either on an outside wall or with horizontal discharge through an interior wall. Raise shower floor enough for a drain. You can break out the slab just enough for the bottom of the trap. Lavitory is through the walls anyway. No slab cut.