OK, I just want to start with, I’m sure I’m overthinking things!
that said, the course says
The image above depicts a free-standing deck (not attached to the home or building). The footing near the home should not be placed in disturbed soil. Disturbed soils are those which have been altered as a result of grading or construction, etc., giving the soil variable characteristics.
I don’t get this. New homes, correcting grading, and other items could cause the need for disturbing soil. Unless the statement means something along the lines of ‘…disturbed soil that hasn’t been properly prepared…’, i’m not getting it.
Tom, I always look for the intent of a specification, whether it’s for a large interstate bridge design or a simple deck in this case. Building codes mainly deal with safety and structural stability. In your case placing footings on undisturbed soil is mainly a stability requirement. You are correct that soils next to a foundation have been disturbed down to a point. But keep in mind some undisturbed soils do not have the capacity to support a structure without modification. In some cases the soil is not used for vertical support at all, like a pile foundation anchored into bed rock. In general a self-supported deck you described would typically require deeper footings next to a basement foundation or a different type of support such as a helical pier. So you need to understand the intent of a building code requirement in order to use it properly.
Understanding intent is a valid point. Where I’m struggling with some of this seems to be that I keep reading over again that we’re not code enforcers. I get the spirit of that point. I also understand our guidance has to come from somewhere, it can’t just be made up by each person in hopes everyone does it the same. What I’m finding is that there is so much of this that comes from code, I’ve not yet tried to review all the codes deriving our guidance. And my black/white mind keeps wanting to say I shouldn’t have to just to finish the course!
I’m worried my “tell me how to do it and I’ll do it that way” brain is messing me up. Not to mention my “everything’s black or white” view of the world.
I guess I’m displeased the direction wasn’t along the lines of “the goal is a footing near the home should not be placed on undisturbed soil. However, in some instances that isn’t reasonable due to soil instability, regrading, or other conditions”
When digging a hole for a foundation, over digging is required for installation. Then comes the backfilling. This section of soil would be considered “disturbed” since it has been dug up and replaced. If a footing for a deck is within this backfill area, the bottom of the footing should be at the same elevation as the footing for the home itself. If it is beyond this area, then it would need to be as deep as specified by the builder’s design requirements or local code.
Even though and excavating contractor may attempt to compact the area to be backfilled along a homes foundation, they typically never get it as good as mother nature did especially when a foundation drain is installed at the homes footing and some sort of settlement will occur. Installing a load bearing structure such as a footing for a deck on soil that will in time settle is bad juju…
This is a very valid point as well. One has to consider the age of the home, possible age of the deck, distance of the footings from the home’s foundation, geographical location, and soil type. Identifying signs of settlement, structural deficiencies, and safety issues are first and foremost.
Spend some time in a new subdivision where decks are being added to houses during construction and talk to contractors. Maybe that will help put things into perspective… just an idea for ya…
Tom, in my previous life I trained over a hundred technicians and engineers on how to read and apply standard specifications, job special provisions, plan reading and how to deal with unforeseen issues that pop up during construction. The best inspectors are able to handle stress, apply the knowledge they learned through training and adapt to challenges they face on a daily basis. Very seldom is construction inspection black and white, same goes for home inspection. In my opinion individuals that see things as black or white never adapted and were unsuccessful at inspection. However individuals with a black or white mindset flourished as designers that are guided by design manuals that enforced rigid steps needed to produce consistent bridge plans or house plans. Unless you can adapt to working in a profession that lives in the gray area, you might try a different profession.
I do appreciate your candor. To try and reframe what I’m trying to convey; stealing from the 7 Habits, seek first to understand. I feel one can only make adjustments and leaps if they have a solid underlying understanding in the first place. In this case, I’m not making sense of the standard as presented.
In the spirit of ‘observation of quantum phenomena can actually change the measured results of this experiment.’, the direction given says not to install on disturbed soil. It doesn’t suggest the goal is to install on undisturbed soil. And as Brian pointed out “But, in most situations, you will not be able to verify (or see) the footing depth so the point is typically mute.”
I don’t feel I understand what point is trying to be conveyed within this requirement about undisturbed soil. And perhaps I’m dwelling on undisturbed too much. I get a solid footing. I get structural stability, bracing, pressure treated, free-standing vs attached, etc… I’m not able to get my mind past this undisturbed soil thing. It must be important, it was put into the course material!
What I’m taking away is that footings are important. But since there’s no way to truly be on undisturbed soil, or verify it’s undisturbedness, do your best to ensure vertical stability, attachment, and safety.
We’ve updated the Footings and Posts sections of the How to Inspect the Exteriors Course and the How to Perform Deck Inspections Course based upon your post and the feedback here. Everyone, please take a look at the updated information. The Education Team appreciates the feedback and how members help InterNACHI keep our curriculum accurate and up-to-date. Thanks!