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Things to Consider Before Building in a Floodplain

Updated: Feb 23



When it rains in the Phoenix Valley, it floods. A majority of Valley residents know exactly what areas to avoid when it rains. As a builder or land developer, this information is crucial for you to know as well. It isn’t always possible to avoid building in floodplains or developing land that is located on, or adjacent to one.


This problem is actually more common than you may think too — up to 41 million Americans live in flood zones, and Arizona had the largest share of the population living in the combined floodplain (64% of the population). Knowing that, here are things that you should consider before building in a floodplain.


What is a Floodplain/Flood Zone?

A floodplain, also known as a flood zone, are geographic areas that the Federal Emergency Management Agency (FEMA) declares at risk of flooding. FEMA ranks every zone for the likelihood and the danger of each flood zone.


How Are Floodplains Identified?

Floodplain Delineation Studies identify areas that have a 1% probability of flooding in any given year. The results of a Floodplain Delineation Study are submitted to the Federal Emergency Management Agency (FEMA) to be incorporated into the Flood Insurance Rate Maps (FIRM).


Information on Maricopa County floodplains can be found here.


Do You Need Flood Insurance?

In some circumstances, yes, but not in all.


In the U.S. all federally backed banks and lenders are required by law to have flood insurance if the borrower is building in a flood zone. As part of the loan process a lender will order a flood certification to determine if the property is in the floodplain.


The sole exception to this law is documentation from FEMA that states your property is outside of the 100-year floodplain. The area of the 100-year (or 1% annual chance) flood is called the Special Flood Hazard Area (SFHA).


If you’re not lending from a bank or financial institution, then you can get your property removed from the floodplain before you start building. To start, hire a land surveyor or civil engineer to help you work through the removal process with FEMA. If you don’t do this first, your request for removal will likely be denied.


Will Flooding Affect Access to the Property?

Another thing to consider is how you will access the property if flooding does occur. For example, picture this: you have a dirt road that leads to where you want to build the home. The dirt road has a large dip in it that frequently gets flooded when it rains. While rain isn’t a concern for a majority of the year in Arizona, it is still an inconvenience to the future homeowner, as they will be unable to enter or leave their driveway if you build it in this same location.


To avoid that, you can either move the road, or fill in the dip to raise it above the floodplain.


Also consider that most local communities are going to require that you also provide drive access to the structure from the street above the floodplain.


The above example is a tame one. If a majority of the property is in a flood zone, then you will want to consider the possibility of an “artificial island” when it rains. This means the possibility of completely isolating the home/building due to rainwater. If this is the case, you’ll need to do some heavy land development to make the land safe and flood-free.


What About Utility Planning?

When you’re in a flood zone, you have to think about underground utilities such as the availability of sewer access, septic tanks, and leach fields.


Many local health departments will not allow the placement of septic tanks and leach fields in 100-year floodplains. Check with your local health department if this is the situation. If there isn’t a large enough area outside the floodplain, you may need to raise part of the property.


Finally, Can My Land Developer Handle the Job?

Not all land developers can handle working in a floodplain. You will want to hire one that has worked on land in flood zones in the past; preferably a local land development company who knows the city codes, state laws, and is certified to do the job.


For example, a local company in Arizona will know exactly where floodplains are located and what areas historically have flooded in the past during monsoon season or random rainfall throughout the year. They will also know which roads are commonly shut down due to flooding, and what nearby amenities are affected as well, such as flooded parks or parking lots. Be sure to ask about their knowledge of the area during your interview with them.


If you are looking for a land developer in the Valley, give us a call at 602-492-9242 or visit us online. Our highly experienced team will be happy to help!


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