MASSACHUSETTS · BARNSTABLE COUNTY
The Cape Reaches Into the Atlantic — and the Wind Reaches Back
A 60-mile sandbar with open water on three sides faces some of the fiercest design winds in Massachusetts: 130–145 mph gusts, hurricanes, and bomb-cyclone nor'easters with nowhere to break the fetch.
PENINSULA GEOGRAPHY · OPEN-WATER FETCH
A Hooked Arm of Sand With Ocean on Every Side
Cape Cod Bay to the north, Nantucket Sound to the south, the open Atlantic to the east — almost no land mass interrupts the wind before it strikes a building.
FETCH-DRIVEN EXPOSURE · ASCE 7-22
Unbroken Salt-Water Fetch Pushes the Cape Toward Exposure C and D
Exposure category is set by the upwind terrain — and on a peninsula this narrow, that upwind terrain is usually water.
Exposure D — Direct Ocean Face
Provincetown, outer Truro and exposed Chatham waterfront with a mile-plus of open Atlantic upwind.
OCEANFRONTExposure C — The Cape's Default
Most near-coastal sites — Wellfleet, Orleans, Dennis, Yarmouth, Barnstable shoreline — sit in open terrain with scattered low obstructions.
MOST SITESExposure B — Only When Sheltered Inland
Reserved for dense, built-up interior pockets of the Upper and Mid-Cape — rare on a sandbar this thin.
INLAND POCKETSWhy fetch matters at 15 ft
Per ASCE 7-22 Table 26.10-1, a 15-ft roof sees Kz = 0.85 in Exposure C but 1.03 in Exposure D — and that gap only widens with height. Calling a true oceanfront site "Exposure C" can leave it under-designed before the velocity-pressure equation even runs.
VELOCITY PRESSURE · qz
What 140 mph Does to a Chatham Rooftop
The same ASCE 7-22 equation that governs every U.S. site, run with Cape Cod's oceanfront inputs.
qz = 0.00256 · Kz · Kzt · Kd · Ke · V²
V = 140 mph
Oceanfront gust, Risk Category II.
SPEEDKz = 0.85
15 ft, Exposure C (Table 26.10-1).
HEIGHTKzt = 1.0
Flat ground; rises near a dune crest.
TERRAINKd = 0.85
Buildings, MWFRS & C&C.
DIRECTIONResult: roughly qz ≈ 36 psf
Far above a sheltered interior-Massachusetts site. Switch the same roof to Exposure D (Kz = 1.03) and the pressure climbs near 44 psf — the difference a single exposure call makes on the Outer Cape.
STORM RECORD · WHY THE NUMBERS ARE HIGH
Bob, Gloria, and the Nor'easters That Wrote the Code
Cape Cod's design winds are not theoretical — recurring tropical and extratropical storms have repeatedly battered the peninsula.
Hurricane Bob, 1991
Gusts to ~125 mph across the Cape — the modern benchmark storm for oceanfront damage.
CAT 2Hurricane Gloria, 1985
Tracked directly over the Cape and Islands, near hurricane-force sustained winds.
CAT 2The 1938 New England Hurricane
Pre-code Cat 3 landfall that set the region's historical hazard baseline.
CAT 3Bomb-Cyclone Nor'easters
The 2018 bomb cyclone and 2013 blizzard drove 80+ mph gusts that can rival a hurricane.
EXTRATROPICALOUTER · MID · UPPER CAPE
One County, Three Wind Zones
Speed and exposure shift as you move from the wave-battered hook to the canal-sheltered shoulder.
| Cape Region | Towns & ZIPs | Design Wind Speed | Exposure |
|---|---|---|---|
| Outer Cape | Provincetown, Truro, Wellfleet, Eastham (02657, 02663, 02667, 02642) | 140–145 mph | C / D |
| Lower Cape | Chatham, Orleans (02633, 02650, 02659) | 135–145 mph | C / D |
| Mid-Cape | Dennis, Yarmouth, Brewster, Barnstable, Hyannis (02639, 02664, 02632, 02630, 02601, 02635) | 130–140 mph | C |
| Upper Cape | Sandwich, Bourne, Falmouth (02563, 02532, 02540, 02541) | 130–135 mph | C / B |
The WindLoadCalc.com calculator reads the exact velocity and exposure from any Cape Cod address or ZIP.
ASCE 7-22 TABLE 1.5-1 · RETURN PERIODS
Higher Stakes, Longer-Return Maps
Risk category doesn't multiply the wind — it sends you to a different basic-wind-speed map with a longer return period and higher mph.
| Risk Category | Map / MRI | Cape Cod Speed | Typical Buildings |
|---|---|---|---|
| I | 300-year | ~125–140 mph | Minor storage, low-occupancy ag/utility |
| II | 700-year | 130–145 mph | Homes, hotels, most commercial |
| III | 1,700-year | ~145–160 mph | Schools, assembly >300 |
| IV | 3,000-year | ~155–170 mph | Hospitals, fire stations, shelters, Seashore critical facilities |
PERMIT-READY · 780 CMR + ASCE 7-22
Six Things a Barnstable County Permit Set Has to Get Right
Cape-specific traps that turn an oceanfront submittal back at the counter.
Pin the Site Velocity
130–145 mph is a range — read the actual map value for the project's coordinates, not a county average.
WIND SPEEDJustify the Exposure Call
Document the upwind fetch — true ocean frontage drives Exposure D, not the default C.
EXPOSURECheck Dune Topography
Elevated coastal dunes lift Kzt above 1.0 near the crest — flat-ground assumptions under-predict.
KztAdd the Nor'easter Case
Extratropical storms aren't optional context — their wind events belong in the design narrative.
STORM TYPESeal It With a MA PE
Calculations must be prepared by or under a Professional Engineer licensed in Massachusetts.
PE SEALCite ASCE 7-22, Current Edition
780 CMR's current cycle references ASCE 7-22 — outdated coefficients fail review.
CODE EDITIONOFFICIAL SOURCES
Where Cape Cod Compliance Comes From
Primary references for Barnstable County wind-load permitting.
KEEP EXPLORING
From the Cape to the Rest of the Map
Statewide context and the tools that handle every coordinate.
CALCULATE WITH CONFIDENCE
Get Cape Cod Wind Loads Right the First Time
WindLoadCalc.com pulls the site velocity, recommends exposure, applies risk category, and outputs PE-ready reports for any Barnstable County address.