Been doing foundation measurements on my inspections and it is rather enlightening.
Here is a 10 month old warranty inspection home. (Yeah it has some magnificent vent stacks and I wonder how far they can go before having to support them) With large cracks. And a heave right in the middle with over 2" of deviation in the slab.
And yes those two little gutters on the front, well that’s all the gutters this house has.
Probably about twenty percent. Maybe a little more. Thing is we look at the whole picture, roof structure, freeze boards, soffits, wall cracks, doors, windows. Everything of course that one normally would without using a zip-level. All to discern weather the foundation appears to be preforming, beginning to fail, or failing. With the disclaimer that we recommend they consult with an engineer regarding any concerns.
In front of a bathroom. Yeah I get what you may be thinking. Heave in the middle, likely a sewer line leaving under the slab. Especially if it were an older house with cast iron. This was 10 months old but still plumbing can leak. They should put a camera in and look.
Oh my bad. Well there were three surfaces to measure, carpet, wood, and tile. The high point was wood which is .4" lower than carpet. We call out the foundation as suspect if it has 1.5" inches or greater measuring the standard deviation of 32 points within 20’ of each other. But really the heave of just over 2" was indiscernible without a zip-level. The spreadsheet is not to scale it just illustrates where a heave is happening.
The other signs of structure or foundation movement were frieze board and trim out of place, some windows had become hard top open and close. Some windows were showing movement in their frame, some base board separation. But not at that specific area.
I see there was a previous question about the zero reference point and also how do I rule out the foundation simply not being level.
The zero reference point is a complex question but I will try to explain.
I check the floor coverings for example carpet, tile, wood. Lucky enough so far with all the new home inspections, most of mine are just less than a year old. So there is not a massive cornucopia of different surfaces. Lets say that they have berber carpet and it is the tallest elevation, the wood and tile are both the same at minus .7" . I create a spreadsheet with 32 measuring points and as I measure I put the floor covering material. I make three tables of 32 points. One has the surfaces with for example carpet at 0 and wood and tile minus .7, Use excel to take my measurements and add the surface difference or lack there of to each point and there I have the actual real measurements. Then I zero that out so that if there was a dip somewhere then that is the zero point. All measurements then are a deviation from the zero of some value.
I never use the measured values to call out a foundation. The call out is consistent and has to do with the whole picture as you sort of eluded to in your line of questioning. “IF” the foundation is better than 1.5" of deviation, “AND” all the other signs exist such as: differential veneer wall cracks, extensive sheet rock cracks over; doors, windows, ceilings, sticking doors, windows out of alignment, cracks in foundation… the list goes on. Then the foundation may “appear to be failing” and recommendation to have it looked at by an engineer. Or say for example if the foundation appeared to have a 1.6" rise, be it cupped, heaved or whatever, but none of the other symptoms exist then that goes into the report. "On the day of inspection no extensive sheet rock cracks, differential veneer … blah blah blah,
Only by special request and usually only if there is a prior survey to compare to. Very rarely
You cannot determine movement from a single point in time measurement. You can determine that the foundation is not level - but not why. You need comparable measurements taken at the same locations at different points in time to determine movement. If you do not establish a zero reference and identify where your measurements are taken, the next guy to come behind you won’t be able to duplicate your measurement for comparison.
I sit my zip level by the stop sign on the corner of the street and zero it out.
Next I check all floor surfaces and record and differences.
Next I record 32 points each within 20 foot of previous and each side.
Then I place them on a chart and zero the chart so that all measurements are from the lowest point. If the lowest point were 72and 3/10" high and I subtract 72 and 3/10 from all the numbers. then I am zeroed on that point. And it is not necessarily at the zip level out on the street by the stop sign on the corner of the street. Correct?
All valid points to a degree that I would not argue against any of them. Accept that I have tested the system I use and even with slight deviations such as what is typically obvious for example a floor tile that is obviously a few tenths higher than the other tiles around it, the results are closely duplicable, even without having the exact same points to measure. Also I have found that with older homes a heave for example found on the spreadsheet can often times show with an uncanny amount of accuracy, where a cracked cast iron sewer pipe might be located, just looking with a camera. But you see the thing about it is. I view the zip level only as a tool that gives one perspective and will be quick to admit that I have no idea of the foundation was poured flat to begin with. I can be a general reference point to be looked at later though and IMO much more useful in new home inspections.
You need to (you don’t really “need” to but it’s beneficial to your client if you do) tell the next guy how to duplicate your measurements and everybody needs to have a basis to compare the two results, including Bubba the foundation guy, who isn’t loading all of this into a spreadsheet to produce a simulated 3D map, along with the homeowner.
Designating a zero reference doesn’t preclude you from doing any of the measurements or graphs that you are doing. However, that’s just thoughts from a guy who doesn’t do these except of relatively rare occasions, hardly an authoritative opinion.