Can You Still Have A Basement in a Floodplain?


WEEK 8: Most of the work occurring on our house elevation project this week are of the unseen nitty-gritty sort. The construction crew is preparing for the return of Payne, our lifting company, by completing the last few foundation projects: aligning the proper height all walls, erecting support beams under the crawl space in the rear of our house, fortifying the cinder blocks, and beginning to fill in the basement.

Can you still have a basement?: No, we will not have a basement in the traditional sense of the word. Historically, the basement evolved as a cool, dry, place to store food and provisions. Over time that idea expanded into habitable living space. As building codes developed, the placement of basement/foundation walls were formally established. In short, foundation walls have to be dug below your area’s frostline. In metro New York, the frost line is four feet deep. That means all the foundation walls have to be dug at least four feet below grade. It makes sense to dig a bit deeper, hollow out that space, and have a usable basement. Ever wonder why so many houses in the northern states have basements vs. those in the south? That’s why. The frost line in many southern states is mere inches. No need to dig as deep and incur an unnecessary expense.

Just because your foundation walls are four feet (or more in colder climates) deep, does not mean you have to hollow out the space and create a ‘basement.’ In fact, in a floodplain, you can not do this. What happens to our current basement? It gets backfilled with gravel and other materials then covered with cement, eliminating any below grade space. This new area is now referred to as the “lowest floor.” By floodplain management regulations, the lowest floor below base flood elevations may only be used for storage, parking, and building access.

As the new foundation wall is constructed, space is allocated for one of the  flood vents.

The new foundation walls are at least four feet below grade, as per proper building code for our location.

In the picture above, our son, Luke, is standing on a ruble pile that was once our basement. Behind him space has been allocated in the foundation wall for a flood vent, a window, and space to remove the steel beams that currently support the house. Once the house is lowered back down onto the new foundation, the gaps for the steel beams will be closed. The flood vent demonstrates where the new floor will be poured. The wooden cribbing will be removed once the house sits on the foundation and is no longer supported by the steel beams supplied by the lifting company.

More things I never planned to learn:  The foundation walls are made of cement cinder blocks fitted with steel rebarb. The rebarb serves to support the cinder blocks along with cement that is meticulously poured down each row of blocks, as seen in the picture below.  The walls will also be a formidable opponent for any flood. (Again, our house does not incur high velocity flooding).

interior of cinder blocks

interior of cinder blocks showing the poured cement

Just in case you can’t get enough information on basements:

http://mccainconstruction.net/basements/ 

http://www.weather.com/news/tornado-central/why-dont-oklahoma-homes-have-basements-20130521

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