Matanuska-Susitna Borough, AK Environmental Rules: Flood Elevation Requirements (2026)
Key Facts
- Residential freeboard
- Lowest floor 2 ft above base flood elevation
- Manufactured homes
- Lowest floor 2 ft above BFE, anchored foundation
- Nonresidential option
- Elevate 2 ft or floodproof, PE certified
- AO zone standard
- 2 ft above depth number, or 4 ft if none
- Critical facilities
- 3 ft above grade or 500-year flood height
Summary
Where base flood elevation data exists, MSB § 17.29.170(A)(1)(a) requires new and substantially improved residential structures in the Matanuska-Susitna Borough's special flood hazard areas to elevate the lowest floor, including any basement, at least two feet above base flood elevation. Nonresidential buildings get an elevate-or-floodproof choice at the same two-foot freeboard.
New construction and substantial improvement of any residential structure shall have the lowest floor, including basement, elevated a minimum of two feet above base flood elevation.
Full Breakdown
The two-foot freeboard in MSB § 17.29.170(A)(1)(a) applies once base flood elevation data has been provided under MSB §§ 17.29.060 or 17.29.130(A)(4). Any fully enclosed area below that elevated lowest floor must either stay empty of habitable use or, per MSB § 17.29.170(A)(1)(b), carry at least two automatic flood-vent openings totaling one square inch of net area per square foot of enclosed space, with the bottom of each opening no higher than one foot above grade.
Nonresidential construction gets a choice under MSB § 17.29.170(A)(2): elevate the lowest floor two feet above base flood elevation like a residence, or floodproof the structure watertight below that level, with a registered professional engineer certifying the design can resist hydrostatic and hydrodynamic loads; floodproofed buildings are flagged for insurance rating one foot below their floodproofed level. Manufactured homes placed outside an existing park, or in a new or expanding park, must sit on a permanent foundation with the lowest floor two feet above base flood elevation and be anchored against flotation and lateral movement (MSB § 17.29.170(A)(3)).
In AO zones, where the FIRM shows only a flood depth rather than a mapped elevation, MSB § 17.29.185 requires the lowest floor at least two feet above the depth number shown, or four feet above the highest adjacent grade if no depth number is given. Critical facilities face the strictest standard: MSB § 17.29.190 elevates their lowest floor three feet above the highest adjacent grade or to the 500-year flood height, whichever is higher, and requires floodproofing and sealing so floodwaters cannot displace toxic substances.
Violations & Fines
Elevating below the two-foot freeboard, or skipping the required engineer's floodproofing certification, is noncompliance under MSB § 17.29.065, which bars construction or alteration in the flood hazard area without full compliance with Chapter 17.29. Enforcement follows MSB Chapter 1.45: a civil penalty up to $1,000 per violation under MSB § 1.45.060(A)(5), with each day the deficient structure exists counted separately under MSB § 1.45.010(C), plus injunctive or restoration relief.
Frequently Asked Questions
How high above base flood elevation must a new house be built in Mat-Su Borough?
Can a business floodproof instead of elevating?
Are critical facilities like fire stations held to a higher standard?
Sources & Official References
Other rules in Matanuska-Susitna Borough
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