Seawall Height in the Keys: Codes, Datums & King Tides
Only Key Colony Beach writes a seawall cap height into its code. Elsewhere in the Lower and Middle Keys, the height comes from the engineer’s design, your survey and the flood rules.
- Top of the capMeasured from a fixed survey reference.
- WaterlineRises and falls with tides and weather.
- Survey reference (datum)A named reference, such as NAVD88.
Use the survey reference printed beside the elevation.
How high should your seawall be?
Your city or county may set a lowest or highest allowed elevation for the top of the wall. The rules can change with the property’s location and the work planned. Drainage, flooding and neighboring properties also affect the design.
For local height rules, use the top-of-cap elevation on your survey. This is the top of the wall measured from a fixed survey reference. It is different from the wall’s bottom-to-top height or the water level.
Find these two items on your survey.
Find the elevation for the top of the seawall cap and the survey reference used with it. The example below shows what to look for.
Seawall cap elevation
- Top of seawall cap
- 6.0 ft
- Survey reference (datum)
- NAVD88
This example shows 6.0 ft NAVD88. Use the number and reference on your own survey.
Match the value and the reference.
- The elevation: use the number for the top of the wall cap, not a building floor, water depth or the wall’s full height.
- The reference: copy the name beside the elevation, such as NAVD88 or NGVD29. You can compare elevations only when they use the same reference.
- Cannot find both? Choose “No / not sure” in the checker. Ask a surveyor to help find them; measuring from the water will give a different result.
What does NAVD88 mean?
NAVD88 is a fixed survey reference used to measure elevations, like a shared zero point. Another survey may use NGVD29 or a tide-based reference. To compare two elevations, they must use the same reference. A surveyor can help if the references differ. Read NOAA’s explanation of survey references.
Look for the seawall cap elevation on your survey or final construction plans. A flood certificate may show only the building’s elevation. If the wall measurement is missing, ask a surveyor; you do not need to measure beside the water.
Repair, replacement and permits
Before raising or replacing the wall, ask the permitting office which rules apply to the work. An engineer can check whether the existing wall, supports and drainage can handle the change. A higher wall can also change where rainwater flows.
Use the permit guide to find the local, Florida DEP and U.S. Army Corps of Engineers contacts. Describe your location and planned work and ask which permits you need. Florida DEP’s application instructions explain the information needed for shoreline projects.
Common questions
How do I plan a change in wall height?
Start with your survey, the wall’s condition and the change you want to make. An engineer can check the supports, drainage and effects on nearby properties. Tell us about your plans and we’ll help you prepare the next step.
Is maximum height the height I must build?
A maximum is the highest allowed elevation, not a target you must build to. Ask your permitting office whether there is also a minimum for your property.
What if I do not know the elevation?
You can start with the property address and what you want to change. A surveyor can identify the top-of-cap elevation and its reference on your survey.
Can an existing seawall be raised?
An engineer needs to check the wall, supports and drainage before recommending a height change. The right approach may involve modifying the wall or replacing parts of it.
Does meeting a number mean the wall is safe?
Height is only one part of the wall’s condition. The supports, drainage and signs of damage also matter. Use the warning-sign check to prepare for an assessment.
How can I get help with the height?
Tell us the property’s city or county and what you want to change. Discuss the next steps, including whether you need a survey or seawall assessment. Confirm any service details and price before going ahead.
Key Colony Beach: the one seawall height rule in code
Of the local codes reviewed for the Lower and Middle Keys, only Key Colony Beach sets a seawall cap height. Sec. 5-51 ties each new wall to the walls beside it. KCB Code Sec. 5-51
| Your situation | Required cap height |
|---|---|
First seawall on the canal | 5.5 feet above mean sea level |
New wall joins existing walls at both ends | Match the higher of the two |
New wall joins one existing wall | Match that wall |
No wall on either side | Match the highest existing seawall on the same side of the canal |
The city also wants a cap 5 to 10 feet wide, and a wall along the lot’s whole water frontage, built at one time. KCB Code Secs. 5-52 to 5-55
- A new wall set in front of a failing one needs a variance from Secs. 5-50 and 5-51. In 2021 the building official said he expected such requests often. KCB P&Z minutes, July 2021
- Elevator-lift forks may not be raised above the seawall cap height. KCB Code Sec. 5-43
The code’s “mean sea level” is an old U.S. Coast and Geodetic datum, not NAVD88. Have a Florida-registered surveyor convert it before you compare it with a modern survey. KCB Code Sec. 5-51 NOAA datum definitions
Monroe County, Key West, Marathon and Layton: no height minimum found
The other local codes reviewed set no minimum cap height for a private seawall. They regulate other parts of the wall instead.
| Jurisdiction | What the code covers |
|---|---|
Unincorporated Monroe County | A cap no more than 2 feet wide, and ground behind the wall at least 6 inches below its top Monroe County code 118-12(k) |
Marathon | A 2-foot cap and a 6-inch swale, berm or curb just landward of the wall Marathon code 106.36 |
Key West | New hardening only for a “critical peril”; the climate plan still being written names no seawall height Key West Code 110-182 Key West Adaptation & Resiliency |
Layton | Plan policy favors riprap, plants or cantilevered platforms over vertical bulkheads Layton Comprehensive Plan 5.d |
No minimum does not mean any height goes. In V and Coastal A flood zones, Monroe County wants a design professional’s analysis that the wall will not push floodwater or reflect waves onto neighbors. Monroe County code 122-31(d)
Key West and Marathon apply the same test in V zones, and Marathon calls the whole city coastal floodplain. Key West Code 34-139(7) Marathon code 107.102.11 City of Marathon floodplain page The permit guide lists the office for your parcel.
King tides, storm surge and sea level in the Keys
A cap height is a bet on future water. These local records help frame it.
- King tides. Monroe County expects seasonal king tides from September through December. It asks for flood photos with address, date and time at greenkeys@monroecounty-fl.gov. Monroe County king tides page
- Measured rise. NOAA’s Vaca Key gauge in Marathon shows relative sea level rising about 1.7 inches per decade from 1971 through 2025. NOAA Vaca Key trend
- Projections. The county adopted the regional Unified projection: 10 to 17 inches of rise from 2000 to 2040, and 21 to 54 inches by 2070. These are planning ranges, not a seawall standard. Monroe County sea level rise page
- Public walls. Key West’s funding request for the Southernmost Point seawall planned a higher cap to address sea-level rise. Key West state funding request, 2023
Storm numbers use different zero points. In Irma, a Marathon high-water mark stood 3.7 feet above ground, while the Vaca Key gauge peaked 2.6 feet above mean higher high water. Hurricane Center Irma report
Never add a surge figure to a survey elevation. Compare elevations only in the same datum. NOAA survey datums
On a king tide, photograph the water against your cap with a tape measure in the frame. Note the date and time. Your engineer gets a local reference no map can give.
Raising a Keys seawall: questions to ask first
A taller cap is design work, and in the Keys it touches several reviews. Ask these before anyone quotes a height.
- Canal or open water? Monroe County allows new vertical walls only on manmade canals, channels and basins, and none on open water. Monroe County code 118-12(k)(3)
- Does a higher cap still count as a repair? The county lets a lawfully existing wall be repaired or replaced while keeping its footprint where practicable. Monroe County code 118-12(k)(4)
- Where will yard water go? County code keeps ground at least 6 inches below the top of the wall, and Marathon requires a 6-inch swale or berm behind it. Monroe County code 118-12(k) Marathon code 106.36
- How will it meet the next lot? Ask the engineer to show the joint with each neighbor’s wall at the property line.
- Who measures? Ask a Florida-registered land surveyor for existing and proposed cap elevations in NAVD88, and for each neighbor’s cap. Florida seawall checklists
If raising means rebuilding, read the seawall replacement guide. If the whole canal is due, see the neighbor planning page.
Show sourcesHide sources
- Code of Ordinances Ch. 5, Art. III Marine Construction and Improvements, Docking of BoatsSource reviewed 2026-10-28
- Planning & Zoning Regular Meeting Minutes, July 21, 2021Source reviewed 2026-10-28
- NOAA tidal datum definitionsSource reviewed 2026-09-05
- Monroe County Land Development Code, Chapter 118 - Environmental ProtectionSource reviewed 2026-10-28
- LDR Sec. 106.36 Criteria For Approval (Hardened Shorelines)Source reviewed 2026-10-28
- Code of Ordinances, Subpart B Land Development Regulations, Ch. 110 Resource Protection, Art. IV Coastal ResourcesSource reviewed 2026-10-28
- Adaptation & Resiliency DivisionSource reviewed 2026-10-28
- Comprehensive Plan Amendment Package (Ord. No. 2022-11-01), adopted June 1, 2023Source reviewed 2026-10-28
- Monroe County Land Development Code, Chapter 122 - Floodplain ManagementSource reviewed 2026-10-28
- Code of Ordinances, Ch. 34 Floods, Sec. 34-139 Other developmentSource reviewed 2026-10-28
- LDR Sec. 107.102.11 Other DevelopmentSource reviewed 2026-10-28
- FEMA Floodplain ManagementSource reviewed 2026-10-28
- King Tides & High TidesSource reviewed 2026-10-28
- CO-OPS Derived Product API: Sea Level Trends, Vaca KeySource reviewed 2026-10-28
- ResiliencySource reviewed 2026-10-28
- Local Funding Initiative Request, Fiscal Year 2024-2025, LFIR #1134: Key West Southernmost Point Seawall RepairSource reviewed 2026-10-28
- Tropical Cyclone Report: Hurricane Irma (AL112017)Source reviewed 2026-10-28
- NOAA National Geodetic Survey datum FAQSource reviewed 2026-10-23
Ask about local requirements
Identify the property and the question to resolve. Keep any available survey with your planning notes.