Single-storey home renovation with no geotech 1

[skeletron]

I usually put 3 boiler plate items in my Foundation General Notes. The first item states (paraphrase) that the Client is responsible for retaining a geotechnical engineer to provide foundation design specifications/recommendations prior to starting construction. The second item states (paraphrase) my expectations for the geotechnical engineer report (ie. site class, bearing, backfill, etc., field review, letter of assurance). The third item states (paraphrase) that "In lieu of available geotechnical specifications, the structural design has assume the following parameters based on typical minimum standards..." and then lists some pretty standard items (bearing pressure used, depth of foundation, etc).

My current project is a single-storey home. Contractor is replacing walls with full side doors, so there are now point loads instead of distributed loads. I was engaged after the contractor got a stop-work order. The backside of a family's house is basically open while they wait for permitting to proceed (not my problem, but damn do I feel sorry for them).

Based on existing maps from the District, I can expect that the ground is soft-sand. My calculations have assumed the worst-case based on the prescriptive values. I've also gone through a couple iterations of what the existing soil pressures were and they seem to jive with the prescriptive values (say max 1000psf). I have designed pad footing extensions to suit this assumed bearing pressure.

The AHJ has now flagged this project and is telling the Contractor that they may need to involve a geotech because of the notes on the structural drawings, and also because there is potential that the District inspector may flag it during there own inspection. The Contractor does not seem to want to engage a geotech (I've provided 2 referrals). Can't tell if this is a cost thing or a "we can't wait another 2-3 weeks to close-up thing" kind of thing. So...

MY QUESTION FOR DISCUSSION
1. Can I provide a written memo to the contractor outlining the risks that they will assume (ie. unknown settlement due to new point loads) by not engaging a geotech and then revise my drawing notes to suit? Basically put wording that kind of waives my liability if there is future drywall cracking or sliding door misalignment due to settlement...
2. Tell the Contractor to *pound sand* (excuse the pun) and get a geotech.
3. Add a field review, assess the ground using the unscientific "I can't shovel the ground anymore" method, and eat a bit of the risk.
4. Don't even worry about it and just revise the drawings to proceed.

I remember there was a similar thread within the last year regarding a similar general subject. So, I'm wondering how others would handle this in practice.

MY INITIAL THOUGHT
Logically, I want to go with #1 but I'm not really sure how enforceable any of that is. Family gets to have their home buttoned up, Contractor gets to complete the work, AHJ no longer has notes to flag the project. This option probably runs in tandem with #3 by default.
In any professional practice resource, the recommendation would probably be to not even take on the project or else go with #2 but I don't practically see this happening with single-family home renovations in my area.

 

[phamENG]

I'd go with number 1, but include the home owner in the conversation and acceptance of risk. Also require that the contractor at least have a geotech assess the excavation to ensure the bearing soils are sound.

My standard notes are similar to yours - design is based on presumptive values, etc....but contractor is required to engage a geotech to verify. Most don't. And the AHJ doesn't care.

 

[Enable]

I would go a hybrid of all your models, which is what we typically do for general things. That is, I assume a prescriptive value for my designs (tends to be between 100-200 KPa) and I have the contractor get a geotechnical firm to site verify that the ground has the assumed capacity. Now, you may engage a geotechnical firm but the person sent to site will be a tech who puts a 10M rebar into the ground and goes "yup...good for that 100 KPa on the drawings".

This costs like $350 Canadian essentially free in your currency (actually I think you might be Canadian....so basically $500 Canadian tire money). If this was an entirely new build on unknown site I would obviously be partial to the whole have a full Geotech report kind of thing. But we're talking about a modification, onto an existing site. Assume a value + call a guy to put a rebar in the ground. That way you're covered, the cost is small, and takes like 48 hours to schedule.

Note: I would NOT be the guy that does the rebar thing yourself. That will likely place you as operating outside of your specialty which might invalidate your insurance.

 

[le99]

For an existing building, the "bearing capacity" should be a "known" from 1) the previous design or 2) evaluating the soil pressure under the existing wall. I don't think there is a need for Geotech involvement at this stage, but the interpretation by a structural engineer (you) to clear the air with the building official who is rigidly "checking the boxes" in the process. You may need to enlarge and deepen the footing to support the concentrated load though.

 

[NorthCivil]

the city probably wouldnt have read your notes at all and raised a stink, had they done things properly with permits and engineering right from the start.

They got caught with their pants down. if they played by the rules, they likely would only need 1 consultant. now because they were naughty, they need two. I wouldnt come to the rescue for these guys, they played with fire and got burned. Why take more liability? they didnt even want to hire you in the first place. There is no goodwill to start with.

In the same spirit, if a client im working with misses calling me for an inspection, and still wants me to sign off (and the risk is acceptable to bear on my part), i still charge them for the missed inspection, plus some. Otherwise, we are rewarding bad behavior. it should never be cheaper to "forget" to call us in, actually, it should be the opposite, it should be more expensive.

 

[skeletron]

Some good and reassuring advice here.
(1) vote for Option #1 with modification
(1) vote for Option #2
(1) vote for hybrid of Option #1 and #3/#2

I agree that the stock notes are likely being flagged because of the improper execution of the project before my involvement. If this was anything but a single-storey little renovation, I'd be a bit stickier about getting a geotech.