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Demystifying FEMA's Lowest Floor Definition and Flood Zone Regulations

jar546

jar546

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FEMA (Federal Emergency Management Agency) defines the "lowest floor" in the context of flood insurance and flood zone regulations. The lowest floor is essentially the lowest enclosed area in a building, with some exceptions. Here's what you need to know:
  1. Definition of Lowest Floor: The lowest floor refers to the bottom level of the building that is fully enclosed, except for areas specifically designed for vehicle parking, building access, or storage.
  2. Prohibited Uses: If the lowest enclosed area is used for anything other than vehicle parking, building access, or storage, it is still considered the lowest floor. Using this area for other purposes violates the requirements set by the National Flood Insurance Program (NFIP). This violation can result in significantly higher flood insurance premiums.
  3. Below-BFE Finished Areas: Any finished areas below the Base Flood Elevation (BFE), including foyers, are not compliant with NFIP requirements. These areas may suffer flood damage that is not covered by insurance, and the building may face increased flood insurance costs.
  4. Basements: In the case of basements (defined as areas below grade on all sides), regardless of how they are used, the floor of the basement is always considered the lowest floor. However, it's important to note that constructing basements in V Zones and A Zones is generally prohibited unless the basement is elevated to or above the flood elevation, or a specific exception has been granted.
  5. Special Requirements for Enclosed Areas Below BFE: In coastal areas, walls of enclosed areas below the BFE must meet special requirements. These requirements are outlined in FEMA Fact Sheet No. 8.1, which covers enclosures and breakaway walls, as well as in Technical Bulletins (TB) 5 and 9 from 2008.
  6. Avoiding Basements in Coastal A Zones: It's emphasized that constructing basements in Coastal A Zones is generally not recommended due to the associated flood risks.
Understanding FEMA's definition of the lowest floor and complying with these regulations is crucial for property owners and builders to avoid violations, ensure proper insurance coverage, and reduce flood-related risks, especially in coastal areas.
 
ASCE 24 says you can not build a house over a basement in a flood zone. Loophole: just call the basement "non-residential", and declare the house plus basement "mixed use". Now the house over the basement is allowed.
 
Non-residential is the relevant terminology.
CFR 44 Chapter 1 Subchapter B Part 59 Subpart A 59.1 Definitions

Other residential building means a residential building that is designed for use as a residential space for 5 or more families or a mixed use building in which the total floor area devoted to non-residential uses is less than 25 percent of the total floor area within the building.

A subgrade basement in a flood zone used solely for storage is allowed for mixed use.

I do not actually think NFIP would ever insure a house with above a basement in a flood zone.
But the faulty definition of "other residential building" creates some uncertainty.
 
guyinsb said:
Non-residential is the relevant terminology.
CFR 44 Chapter 1 Subchapter B Part 59 Subpart A 59.1 Definitions

Other residential building means a residential building that is designed for use as a residential space for 5 or more families or a mixed use building in which the total floor area devoted to non-residential uses is less than 25 percent of the total floor area within the building.

A subgrade basement in a flood zone used solely for storage is allowed for mixed use.

I do not actually think NFIP would ever insure a house with above a basement in a flood zone.
But the faulty definition of "other residential building" creates some uncertainty.
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Homes over basements that are below BFE are built on a daily basis and compliant with all FEMA and NFIP requirements, hence the wet-floodproofing requirements. Some municipalities & states have stricter requirements than FEMA, especially those participating in the CRS. Any new construction built below BFE can only be used for parking, access to the property, and storage. These areas need flood vents and other wet-floodproofing designs incorporated into the construction.

On a personal note, I think people are idiots for building anything below BFE. It is, however, allowed.
 
"Below-grade areas, including areas used for parking, are not permitted under residential buildings in SFHAs identified as Zone A."

See NFIP Tech Bulletin 6 January 2021 page 1.
 
guyinsb said:
"Below-grade areas, including areas used for parking, are not permitted under residential buildings in SFHAs identified as Zone A."

See NFIP Tech Bulletin 6 January 2021 page 1.
Click to expand...
That is for dry-floodproofing only. The entire bulletin you reference is specifically for dry-floodproofing. You can't take one section of the requirement and apply to to others.
 
I am using FEMA's definition of a basement (sub-grade on all 4 sides). There is no way for water to flow out of a basement. But even worse, there is no way for water to freely flow in to a basement. Result? Exterior hydrostatic pressure builds up, and the basement walls collapse.
 
guyinsb said:
I am using FEMA's definition of a basement (sub-grade on all 4 sides). There is no way for water to flow out of a basement. But even worse, there is no way for water to freely flow in to a basement. Result? Exterior hydrostatic pressure builds up, and the basement walls collapse.
Click to expand...
The height of BFE in relation to the foundation is key.

Your position is that it is not allowed at all. My position is that it is, even though I don't like it, or agree it can be done, which it can.

From the ASCE-24
2.7.3 Installation of Openings Installation of openings shall meet the following criteria:
1. Each enclosed area shall have a minimum of two openings,
2. Openings shall be in at least two walls of each enclosed area,
3. The bottom of each opening shall be no more than 1 ft above the higher of the final interior grade or floor and the finished exterior grade immediately under each opening, and
4. Openings meeting requirements of Section 2.7.2.1 or Section 2.7.2.2 that are installed in doors and windows are permitted.


I've worked directly with FEMA and have seen this done legally in two different states. What you and I like and agree with and what is allowed are two different things.
 
The ASCE section you cite is not applicable to a basement (ASCE's definition of a basement). The area below the first habitable floor is not necessarily a basement. This is a common misunderstanding.
But ASCE 24 is explicit (page 61): "The standard permits basements in nonresidential structures but prohibits basements in residential structures."
 
guyinsb said:
I am using FEMA's definition of a basement (sub-grade on all 4 sides). There is no way for water to flow out of a basement. But even worse, there is no way for water to freely flow in to a basement. Result? Exterior hydrostatic pressure builds up, and the basement walls collapse.
Click to expand...
Flood loads are addressed in IBC 1612
 
guyinsb said:
The ASCE section you cite is not applicable to a basement (ASCE's definition of a basement). The area below the first habitable floor is not necessarily a basement. This is a common misunderstanding.
But ASCE 24 is explicit (page 61): "The standard permits basements in nonresidential structures but prohibits basements in residential structures."
Click to expand...
The section I posted is reference to from coastal A and VE zones further along. Enclosed areas below DFE are allowed in the high hazard area for coastal construction found in chapter 4. Again, you can't read one thing and apply it across the board, especially when it is referenced.
 
guyinsb said:
The ASCE section you cite is not applicable to a basement (ASCE's definition of a basement). The area below the first habitable floor is not necessarily a basement. This is a common misunderstanding.
But ASCE 24 is explicit (page 61): "The standard permits basements in nonresidential structures but prohibits basements in residential structures."
Click to expand...
Too bad they don't have to publish the law and then there would be a way for everyone to see it....
 
The "enclosed area" is the source of the confusion. A basement is treated more strictly than an enclosed area. Water can freely flow out of an enclosed area (if openings are provided). That is not the case for a basement.
 
guyinsb said:
The "enclosed area" is the source of the confusion. A basement is treated more strictly than an enclosed area. Water can freely flow out of an enclosed area (if openings are provided). That is not the case for a basement.
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It's not about getting the water out. It is about equalizing pressure.

You are misapplying the requirements and making them more restrictive than they are.
 
jar546 said:
It's not about getting the water out. It is about equalizing pressure.

You are misapplying the requirements and making them more restrictive than they are.
Click to expand...
 

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I live literally a block away from the river that provides a 3rd of the water in the Cheasapeake Bay in a house from 1930 with a basement and somehow it is flood insurance exempt based upon 1st floor level height. I'll never understand how but will gladly not pay hundreds of dollars a month in flood insurance fees . BTW most of the surrounding properties do have flood insurance required.
 
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