Manufactured Homes, Recreational Vehicles & Accessory Structures

Manufactured Homes, Recreational Vehicles & Accessory Structures

Manufactured Home Elevation & Anchoring Rules

Manufactured homes (often colloquially referred to as mobile homes) are particularly vulnerable to flood damage. Due to their lighter construction and the way they are typically placed on foundations, they are highly susceptible to flotation, lateral movement, and severe wind damage during coastal storms or fast-moving riverine floods.

Under the NFIP, a manufactured home placed or substantially improved within an SFHA must meet the same basic performance standards as a traditional site-built residential structure.

• Elevation: The lowest floor of the manufactured home must be elevated to or above the Base Flood Elevation (BFE). Outside the existing-park exception, new manufactured homes in SFHAs must be elevated so the lowest floor is at or above the BFE and securely anchored. 44 CFR 60.3(c)(12) still provides a limited exception for manufactured homes placed or substantially improved on sites in an existing manufactured home park or subdivision: the chassis may be supported by reinforced piers or equivalent foundation elements that are no less than 36 inches in height above grade, and the home must still be securely anchored. If the BFE is higher than that 36-inch height, communities commonly require elevation to the BFE as a higher standard—but the federal minimum text retains the existing-park pathway. V/VE placements follow coastal foundation rules, not slab-on-fill shortcuts.
• Anchoring: The home must be securely anchored to an adequately anchored foundation system to resist flotation, collapse, and lateral movement. This typically requires over-the-top ties, frame ties, or specialized ground anchors driven deep into the soil. The anchoring system must be designed to withstand the specific hydrodynamic and wind loads expected at the site.
• Foundation: The foundation itself (piers, blocks, columns) must be designed to remain stable under flood conditions. Dry-stacked concrete blocks are generally insufficient and illegal in floodplains unless specifically engineered, reinforced with steel rebar, and filled with concrete to prevent them from toppling over in moving water.

Recreational Vehicles: The 180-Day Rule

Recreational Vehicles (RVs) present a unique regulatory challenge. They are designed for mobility, but they are sometimes used as permanent or semi-permanent residences in scenic areas like riverbanks or coasts. If an RV is permanently placed in a floodplain, it faces the same risks as a manufactured home, often with even less structural integrity.

To balance the intended mobility of RVs with flood safety, the NFIP enforces the 180-day rule for RVs placed in an SFHA. To be exempt from elevation requirements, an RV must meet one of two strict conditions:

1. Be fully licensed and ready for highway use AND be on the site for fewer than 180 consecutive days. "Ready for highway use" means it is on its wheels or jacking system, is attached to the site only by quick-disconnect type utilities (plug-in electricity, hose for water) and security devices, and has absolutely no permanently attached additions like screen rooms or large decks. The goal is that if a flood warning is issued, the owner can hitch the RV to a truck and drive it out of the hazard area immediately.
2. Meet the elevation and anchoring requirements for manufactured homes. If the RV is placed on concrete blocks, has a built-on deck, has its wheels removed, or remains on site for 180 days or more, it is treated legally as a manufactured home. It must then be elevated to the BFE and permanently anchored to the ground.

Small Accessory Structure Exemptions

Accessory structures are buildings that are subordinate to and on the same parcel as a principal structure, such as detached garages, storage sheds, or small pole barns. Requiring a small, low-value shed to be elevated on pilings to the BFE is often impractical, unsightly, and cost-prohibitive for the homeowner.

FEMA policy allows communities to grant exemptions for certain small accessory structures, permitting them to be built below the BFE without going through a formal, difficult variance process, provided they meet strict mitigation criteria designed to minimize damage.

To qualify for this exemption, the accessory structure must meet all of the following conditions:

• Use Limitation: It must be used solely for parking of vehicles or limited storage. It cannot be habitable space, a workshop, a business, or used for the storage of hazardous materials.
• Size Limitation: While FEMA guidance suggests these should be "small" (often interpreted as under 600 square feet, though communities may set their own limits in their ordinances), the key is that it represents a low-value investment and is subordinate to the main house.
• Wet Floodproofing: The structure must be designed to allow floodwaters to enter and exit automatically, equalizing hydrostatic pressure on the walls. This requires the installation of compliant flood openings (vents).
• Anchoring: It must be firmly anchored to prevent flotation. A floating shed can become a battering ram that damages nearby homes.
• Materials: All construction materials used below the BFE must be flood-resistant materials (e.g., treated lumber, concrete, metal).
• Utilities: Any mechanical or electrical equipment must be elevated above the BFE or designed to be watertight.

By ensuring the structure can flood without collapsing (wet floodproofing) and restricting its use to non-valuable purposes, the community minimizes the economic loss and safety risk associated with these accessory buildings.