Borderline (expensive) foundation problem

[Matthew Samson]

We plan to turn our current house hack into a long term rental. We just discovered a crack in the concrete slab foundation that is a borderline major problem:
- It is a vertical crack about 1/8 inch wide that is at least 9ft long, which is causing a 3/4 inch drop in the flooring and some evidence of old (luckily) limited moisture and termite intrusion. 
- BUT, it also appears old and probably a symptom of the original house settling. It has not caused any noticeable structural issues. We know that some settling is inevitable on all slabs. 

The options we have are: 
- Do nothing and keep monitoring the crack.
- Seal the crack only from above and hope it stays static.
- Stabilize the foundation with helical piers on the exterior. 

The helical piers system would cost $25k but is a permanent solution. Is it overkill for a potential non-problem? Would the fact that our house is in the ~ $850k valuation range influence your advice? 

Even if you don't feel you have enough info to give me directional advice, how would you go about deciding whether to address the problem? 

[Laura Shinkle]

@Matthew Samson that's a tough break, sorry to hear about that. I've worked with a client in a very similar situation, and have spoken to many inspectors/engineers/builders, etc about things like this. *keep in mind I'm none of those things, always rely on the experts*

1. I'd get an actual structural engineer out to the property. They don't have a monetary incentive to sell you on anything. They'll charge $500-$1k (at least in my area) to come out, evaluate the home, and give you a plan. You can then take that plan to foundation companies and get bids for that work. 

2. For the issue itself, the crack isn't necessarily my biggest concern, but the displacement of the foundation is what worries me. Even if it's 10 years old or more, the potential for shifting is still there and you may have been structurally compromised for years and just not known. 3/4 inch displacement is fairly significant (IMO) for a slab foundation. 

3. Side note, and not what you're asking...I'd make sure you get a termite bond on the house. It's basically yearly treatment to protect the home from termites. If you've got evidence of them in the past, they could come back (and yes, I've had termites in two of my slab foundation homes, so it's definitely possible and happens, at least in my area which is NC). 

4. $25k for helical piers sounds a little steep, but it's been a few years since I saw a quote for that, and of course it depends on how many you need. Again, get a structural engineer out there to evaluate and go from there. 

Good luck!!