Coastal Corrosion Risk Guide by Address

Estimated time: 3 minutes

Salt-air corrosion is the single biggest threat to metal roofing on the Gulf Coast. The right specification depends on how far your home sits from saltwater. Select your distance below and get specific substrate, coating, and fastener recommendations — with explanations for each.

Step 1: How far is your home from saltwater?

This means the straight-line distance from your home to the nearest body of saltwater — the Gulf of Mexico, a saltwater bay, tidal creek, or brackish bayou. If you are unsure, estimate conservatively (choose the closer distance).

Why does distance matter so much?

Airborne salt concentration drops exponentially with distance from the shoreline. Within 1,500 feet, salt deposition rates can be 10-50 times higher than at 5 miles inland. This directly determines how fast protective coatings and metallic layers degrade.

Other factors also matter — prevailing wind direction, elevation, vegetation barriers between your home and the water — but distance is the single strongest predictor of salt exposure and the primary basis for manufacturer warranty zones.

Understanding Your Results

Why Distance Is the Primary Factor

Airborne salt concentration follows a predictable decay curve as you move inland from the shoreline. Researchers measuring chloride deposition along the Gulf Coast have consistently found that salt levels drop by roughly 80-90% within the first mile from the water, with the steepest decline occurring in the first 1,500 feet. This is why that 1,500-foot threshold appears in virtually every metal roofing manufacturer's coastal installation guide.

The remaining salt that reaches 1-5 miles inland is enough to affect material selection — it accelerates coating degradation and fastener corrosion compared to truly inland environments — but it is manageable with standard high-quality specifications. See our moderate zone guide and standard zone guide for detailed recommendations ( substrate, coating, quality fasteners).

Factors That Can Shift Your Zone

Prevailing wind direction. Homes directly downwind of the Gulf receive more salt than homes on the lee side of a peninsula, island, or headland. Along the Mississippi and Alabama Gulf Coast, the prevailing summer winds come from the south and southeast, pushing salt air inland. If your home faces the Gulf with no wind break, consider specifying one zone more conservatively.

Elevation. Homes at higher elevation relative to the waterline receive less salt spray. Our substrate comparison guide covers the corrosion science behind each recommendation. Homes at higher elevation than homes at water level, even at the same horizontal distance. A home on a bluff 50 feet above the shoreline at 1,000 feet distance may experience salt levels more typical of the moderate zone than the severe zone.

Vegetation and buildings. Dense tree canopy, buildings, and other structures between your home and the water act as physical barriers that capture airborne salt before it reaches your roof. A heavily wooded lot 1,200 feet from the water may experience significantly less salt than an exposed lot at the same distance.

Saltwater body type. The Gulf of Mexico shoreline produces the most aggressive salt exposure. Saltwater bays (Biloxi Bay, Mobile Bay, Perdido Bay) produce moderately aggressive exposure. Brackish bayous and tidal creeks produce less salt than the open Gulf but more than freshwater. If your nearest saltwater is a bay or bayou rather than the open Gulf, your actual exposure may be somewhat lower than the distance-based zone suggests.

When to Specify Beyond the Minimum

The recommendations in this guide are minimums for each zone. There are good reasons to exceed them:

  • If you plan to live in the home for 30+ years, specify one level up from the minimum. The marginal cost of upgrading from SMP to PVDF, or from Type 304 to Type 316 stainless, is small relative to the decades of additional service.
  • If the roof is difficult or expensive to access (steep slope, multi-story, complex geometry), invest in materials that will not need early maintenance or replacement. The labor cost of future repairs or re-fastening on a difficult roof far exceeds the material upgrade cost.
  • If you are near the boundary between zones, specify for the more aggressive zone. The cost difference between adjacent zones is modest, and the penalty for under-specifying is a roof that fails before its time.