Can I dig a foundation below flood elevation outside the Floodplain?

Question

Looking for answers from people building foundations near (not in) the 100 year floodplain. Does this trigger a floodplain build permitting process? Am I basically pigeonholed into a monolithic pour to avoid this? No one working on my foundation (excavators, concrete company etc) seems to know the answer or they think I should just "not worry about it".

My question is 100% a FEMA rules / what is allowed question. Not at ALL interested in whether I "should" or not. To dissuade your fears: This is a field in Montana near a creek that hasn't flooded the site in the last 100 years. I have some control over the flow in the creek. There are hundreds of houses around me, (many lower) which have never flooded (in 100 years). Even if this is all a terrible idea, I simply think it's worth the risk.

I DO care about the county or FEMA saying I did something wrong / making me change it. And, I DO care about a mortgage company forcing flood insurance (showing I am somehow in a floodplain) - pretty sure that won't happen however.

A picture says a thousand words:

Floor joists and the entire home and all electrical, 100% of everything is above the flood plain elevation.

I must: Apply for a permit for any modification or even moving a rock inside the 100 year floodplain. Does this count since I'm digging beneath it? The county did not specify and there no building permits in this county. They were adamant on proving my site is outside the 100 year floodplain (unless flood plain permitted).

Answer 1

The flood plain issues I had to deal with is more about the openings in the foundation to allow water to exit. As others have said have a Survey, my current home was in the flood plain until the survey , huge insurance jump because the lender required flood plain insurance until the survey. I am planning on an additional 3 car garage the county is the one that issue the permits, not fema.

If the county asks show them the structure is not in the flood plain, when you get your permit build to your plot plan and you will be fine. I have a friend that built a house on poles to put the structure above the flood plain his footings for the poles were well below the 8’ or more “level identified as the 100 year level” the county only required engineering stamps on the plans, just like roof trusses require in most locations. He has never had to have flood insurance.

Don’t bring up issues that you don’t want to deal with because as you said they go to the ultra safe side because they don’t want to be wrong. After living through several 500+ year floods he started enclosing the lower section I have not talked to him but last time I was in Corvallis the entire lower 1/2 was enclosed.

Monolithic pours are not the only way to go but you are not in the flood plane so get your permit. Make sure you plan for drainage like a French drain under the low side with a heavy footing above that for insurance that it will drain this doesn’t have to be on the plans. So submit your plot plan to the county and pay the fee. If they ask , show the survey. When approved start building and enjoy your home.