Walk down almost any street on Treasure Island, Madeira Beach or the Redingtons and you will see homes raised up on pilings or block walls. The living space is up top. Underneath is parking, a storage room, maybe a stairway or elevator. That lower level looks simple, but it is one of the most regulated parts of a coastal home.
This post explains how flood vents and breakaway walls work, how the rules differ by flood zone, and what you can and cannot do with the space below.
Start with your flood zone
Your flood zone sets the rules. On the Pinellas barrier islands, most homes fall into one of these:
- A zones (including AE). High-risk flood areas where rising water is the main concern.
- Coastal A zones. Areas within an A zone that can see moderate breaking waves. On FEMA maps they often sit between the shoreline and a line called the Limit of Moderate Wave Action, or LiMWA.
- V zones (including VE). Coastal high hazard areas exposed to storm surge with stronger wave action.
You can find your zone on your elevation certificate, your flood insurance declarations page, or FEMA's flood map service. Your city's floodplain administrator can confirm it too.
Flood vents in A zones
In A zones, FEMA's rules allow a solid enclosed area under an elevated home as long as the walls have flood openings, often called flood vents. These openings let water flow in and out during a flood. That keeps the water level inside and outside about the same, so the pressure does not push the walls in.
According to FEMA Technical Bulletin 1, non-engineered flood openings have to meet a few basic rules:
- At least two openings for each enclosed area.
- A total net open area of at least one square inch for every square foot of enclosed area.
- The bottom of each opening no higher than one foot above grade.
- Openings on more than one side of the enclosure, so debris is less likely to block them all.
There are also engineered flood vents. These are products certified by a registered engineer or architect to perform at least as well as the basic sizing rule. They often allow fewer, smaller openings. Your designer and building department will check that the vents shown on your plans match the certification.
Do not block your vents. Covering flood vents with plywood, insulation or stored items can defeat their purpose, and it can also cause problems on your elevation certificate and flood insurance rating.
Breakaway walls in V zones
V zones work differently. FEMA rules say the area below an elevated home in a V zone has to be free of obstruction, or enclosed only with one of these:
- Open lattice.
- Insect screening.
- Non-supporting breakaway walls.
A breakaway wall is built to collapse under flood and wave forces without damaging the elevated house or its foundation. FEMA Technical Bulletin 9 explains that NFIP rules call for a design safe loading resistance between 10 and 20 pounds per square foot. In plain terms, the wall needs to stand up to everyday wind but give way when storm surge hits it.
A few other points from Technical Bulletin 9 are worth knowing:
- Breakaway walls should be built with flood damage-resistant materials.
- Electrical, plumbing and mechanical components should not be mounted on or run through breakaway walls.
- The NFIP alone does not require flood openings in V zone breakaway walls, but newer building codes and the ASCE 24 standard do. So you will often see vents in breakaway walls too.
Coastal A zones: often treated like V zones
Coastal A zones are the gray area that catches people off guard. FEMA notes that the 2015 and later International Codes treat Coastal A zones like V zones for breakaway wall rules where a LiMWA is shown on the map. Florida's building code and local flood ordinances also have Coastal A provisions. If your lot is in a Coastal A zone, plan on V zone style construction below the house until your building department tells you otherwise.
What you can use the space for
FEMA guidance is clear on this. An enclosed area below an elevated home can be used only for:
| Allowed | Not allowed |
|---|---|
| Parking vehicles | Bedrooms, offices or living areas |
| Building access, like stairs, an entry foyer or an elevator | Finished drywall, carpet and other materials that are not flood resistant |
| Storage | Bathrooms or kitchens |
| Appliances and HVAC equipment below the required elevation |
Converting the space into a game room or guest suite is one of the most common violations on the beaches. It can put your flood insurance at risk and can lead to code enforcement. Many Florida communities ask owners to sign a nonconversion agreement when they get a permit for an elevated home, which is a promise that the lower area stays within these limits. Ask your city whether it uses one.
Some communities in the area also limit the size of enclosures or require extra elevation above the base flood elevation, called freeboard. Those rules vary by city, so confirm with the building department in Treasure Island, Madeira Beach, Redington Beach, North Redington Beach or Redington Shores before you design anything.
This article is general information, not legal or insurance advice. Flood rules depend on your flood zone, your city's ordinance and the current Florida Building Code. Confirm the requirements for your property with your local building department and talk with your flood insurance agent about how your enclosure affects your policy.
Smart ideas for the space below
- Use concrete, pressure-treated wood and other flood damage-resistant materials.
- Keep storage on shelving you can move upstairs before a storm.
- Plan electrical outlets and switches carefully with your designer and keep them within code limits.
- Keep the area around flood vents clear.
- If you are building new, think about parking, storage and access early. Good planning makes the space useful without crossing the line.
Building new or raising your home?
If you are weighing whether to lift an older home or start over, our post on raising or rebuilding on Treasure Island walks through the options. Our FEMA 50 percent rule guide explains when an existing home has to come into compliance.
Planning an elevated home on Treasure Island, Madeira Beach or the Redingtons? Contact AllPhase and we can talk through your lot, your flood zone and how to plan the space below. You can also read more about our elevated home building work on the islands.
Common questions
Can I finish the area under my elevated home?
No. FEMA rules limit enclosed areas below an elevated home to parking, building access and storage, and they must be built with flood damage-resistant materials. Finishing it as living space can affect your flood insurance and lead to code violations.
How many flood vents do I need?
Under FEMA Technical Bulletin 1, non-engineered vents need at least two openings per enclosed area with one square inch of open area for every square foot of enclosed space. Engineered vents follow their certification instead.
What is a breakaway wall?
It is a non-supporting wall below an elevated home in a V zone, and often a Coastal A zone, built to collapse under storm surge without damaging the house or foundation.