Structural Engineer Serving Westerly, Rhode Island

South County Design Group, Inc. is a local Rhode Island engineering firm focusing on structural engineering services. Since 2003 we have served clients throughout the state, with particular focus on coastal residential projects in Westerly and the southwestern Rhode Island coast. The firm is led by Kenneth A. Hayes, Rhode Island Professional Engineer (License #7252).

This page summarizes the structural and coastal design parameters that apply to Westerly under the Rhode Island State Building Code as revised effective December 1, 2025, and describes our professional approach to determining design wind loads for specific sites in the town.

Westerly Design Parameters Under the New Code

Rhode Island's State Building Code (RISBC) was updated effective December 1, 2025. For the first time, the code publishes a single set of design values per municipality — used by both residential (RISBC-2) and commercial (RISBC-1) projects.

Below is a plain-English summary of the wind, snow, temperature, and frost-depth values that apply to structures in Westerly, followed by how we translate them to a specific property.

Westerly · RISBC Design Parameters

Parameter	Value
Ground snow load	30 psf
Flat roof snow load	30 psf
Ultimate design wind speed (Vult), Risk Category I	120 mph
Vult, Risk Category II	137 mph # — WBDR applies within 1 mile of coast
Vult, Risk Category III	138 mph #
Vult, Risk Category IV	142 mph * — WBDR applies regardless of coast proximity
Frost depth (residential, RISBC-2)	3'-4"
Frost depth (commercial, RISBC-1)	4'-0"
Winter design temperature (Washington County)	5°F
Mean annual temperature	50°F
Air freezing index	1,200 degree-days below freezing

Risk Category II is the default for most residential and commercial structures. Risk Category III applies to important facilities (assembly occupancies of more than 300, schools with more than 250 students, certain healthcare uses). Risk Category IV covers essential facilities (hospitals, fire stations, emergency operations centers, designated emergency shelters).

The Wind-Borne Debris Region in Westerly

The Wind-Borne Debris Region (WBDR) is the coastal zone where windows are most likely to be struck by flying debris during a hurricane. Inside the WBDR, openings must either use impact-resistant glazing or approved shutters — otherwise the structure must be designed as partially enclosed, which substantially increases the wind loads it has to resist. Glazing inside the WBDR must pass the Large Missile Test of ASTM E1996 and ASTM E1886.

Under the new RISBC, a site falls within the WBDR when both conditions are met:

1. The structure's Risk Category design wind speed (V_ult) is 130 mph or greater; and
2. The structure is within 1 mile of the "mean high coastal water line."

For Westerly at Risk Category II, V_ult is 137 mph — well above the 130 mph threshold, carrying the # flag. Any Risk Category II residence within 1 mile of a qualifying coastal shoreline falls within the WBDR and requires impact-resistant glazing. Westerly's V_ult is among the highest in Rhode Island, reflecting its open Atlantic exposure at the state's southwestern tip.

What Counts as "Coastal" in Westerly

The new RISBC references "mean high coastal water line" without defining the term. In our practice, we interpret "coastal" consistent with the ASCE 7-16 Exposure Category D framework — the wind-load engineering standard the code references. Under ASCE 7-16, a water body produces coastal conditions when its upwind fetch exceeds 5,000 feet — enough open water to generate the wind characteristics that put a structure in Exposure Category D.

Applied to Westerly, this interpretation identifies the qualifying shorelines as:

• The open Atlantic coast — along Misquamicut State Beach, Misquamicut, Weekapaug, Napatree Point, and Watch Hill
• Winnapaug Pond — tidal salt pond with extensive fetch
• Little Narragansett Bay — at Westerly's western/southwestern border with Connecticut (Stonington)
• The Pawcatuck River — tidal along its lower reaches to Little Narragansett Bay

Smaller water bodies — the upper Pawcatuck River, Chapman Pond inland — do not generate 5,000-foot fetches and do not produce Exposure D conditions. Structures near them fall into Exposure C.

The technical framework behind these design decisions is laid out in our references on Wind Exposure Categories in Rhode Island (Exposure B, C, and D explained), coastal flood-zone designations (V-Zone, Coastal A Zone, and A-Zone foundation rules), and Net Zero Engineering for Rhode Island Homes (high-performance envelope and integrated solar/storage design for coastal new construction).

Two Distance Rules, Two Distinct Zones

Under ASCE 7-16 §26.7.3 (preserved in ASCE 7-22 §26.7.4), coastal proximity drives two separate design requirements with different distance thresholds:

ASCE 7-16 / 7-22 · Coastal Distance Framework

Distance From Qualifying Shoreline	Effect
Within 600 feet (or 20 × mean roof height, whichever is greater)	Exposure Category D — the highest wind exposure category, producing the largest design wind pressures
Within 1 mile of mean high coastal water line (and Vult ≥ 130 mph)	Wind-Borne Debris Region — impact-resistant glazing or approved shutters required
Beyond the 600-foot Exposure D zone but still within the 1-mile WBDR zone	Exposure Category C with WBDR requirements — standard open-terrain wind pressures, plus impact-rated openings
Beyond 1 mile from any qualifying shoreline	Exposure Category C — no WBDR requirement

A typical coastal Westerly residence sits within all three concentric zones: within 600 feet of a qualifying shoreline (Exposure D), within 1 mile (WBDR), and statewide well above minimum V_ult. The shoreline neighborhoods of Misquamicut, Weekapaug, Napatree, Watch Hill, and the Winnapaug Pond frontage typically fall in this combined Exposure D plus WBDR condition. Homes further back from the coast may leave the 600-foot Exposure D zone while remaining within the 1-mile WBDR. Inland Westerly — Bradford, Potter Hill, Dunn's Corners, Quigley Corner, and the interior neighborhoods north of Route 1 — sits outside both zones.

Neighborhood-Level Structural Considerations in Westerly

Westerly's coastline runs from the Connecticut border at Watch Hill east through Misquamicut and Weekapaug to the Quonochontaug boundary with Charlestown. Each of these named shore communities has its own structural design character, shaped by geology, exposure, and how each fared in the 1938 Hurricane. The contrast among them is sharper than between most other Rhode Island towns.

The Misquamicut Tier

Atlantic Avenue and the residential streets between Misquamicut Beach and Winnapaug Pond hold the most exposed land in Westerly. This is open Atlantic frontage with Exposure Category D, inside the WBDR, and FEMA VE Zone across most of the beach blocks. The 1938 Hurricane destroyed 369 homes in Misquamicut, 282 of them on Atlantic Avenue alone, killing 41 residents. Hurricane Sandy (October 2012) devastated the area again; many surviving structures were demolished, relocated, or substantially elevated above Base Flood Elevation as part of the post-Sandy rebuild. V-Zone open foundations on driven or helical piles are now standard practice for new and substantially renovated Misquamicut residences.

The Watch Hill and Napatree Tier

The high ground of Watch Hill village, Watch Hill Cove frontage, and the now-uninhabited Napatree Point spit exhibit a striking contrast with Misquamicut despite being only a few miles to the west. Watch Hill's underlying till substrate and elevated terrain provided meaningful protection in 1938: damage was severe but not catastrophic in the village proper. Napatree Point, the low sand spit projecting west of Watch Hill, had 44 homes before 1938; the hurricane obliterated all of them, and Napatree was never rebuilt — it is now conservation land. Watch Hill village remains subject to the Watch Hill Historic District overlay; structural work on contributing historic structures requires Historic District Commission review in addition to standard permits.

The Weekapaug Tier

Weekapaug Breachway, Weekapaug Point, and the Atlantic Avenue extension east of Misquamicut fared dramatically better than their neighbors to the west in 1938: 1 death and 23 homes destroyed. The reason was bedrock and till substrate underlying parts of Weekapaug Point, plus a slightly higher beach profile. Modern Weekapaug shore construction nonetheless follows the same V-Zone and WBDR rules as Misquamicut; the geology buys margin, not exemption.

The Inland and Upland Tiers

Downtown Westerly along the Pawcatuck River, the Avondale neighborhood, Bradford to the north, and the upper Westerly Hills sit outside the coastal WBDR. Most inland properties fall in Zone X or AE (river-flood related along the Pawcatuck) and qualify for Exposure C or B depending on upwind cover. Frost depth (3'-4" residential, 4'-0" commercial) and the 30 psf ground snow load govern foundation and roof design here.

Soils and Geology Specific to Westerly

Misquamicut and the Weekapaug shoreline sit on south-coast glacial outwash — sandy, well-drained, with low bearing capacity in places. Watch Hill and parts of Weekapaug overlie till and rock, which explains the 1938 survival differential among neighbors only a few miles apart. Inland areas transition to till-mantled bedrock common across northern Westerly. The town also publishes a Coastal Erosion guidance page documenting shoreline change and current municipal positions on erosion control.

Historical Storm Record

The 1938 Hurricane is the defining event in the structural record of Westerly's south coast: 41 dead, hundreds of homes destroyed, the obliteration of Napatree's residential community. Hurricane Carol (1954) and Hurricane Bob (1991) added further damage. Hurricane Sandy (2012) reshaped the Misquamicut waterfront for a second time in less than a century. The town's modern shore construction now operates on the assumption that 1938-class events are not historical anomalies but periodic design-life loads.

Local Permitting

Building permit review is handled through Westerly's Building Office at Town Hall (45 Broad Street), with electronic submission through the OpenGov permitting portal. Coastal portions of town fall under CRMC Salt Pond Region SAMP, covering roughly 15% of Westerly's land area.

How We Determine Wind Load for a Specific Westerly Site

The RISBC publishes a single V_ult value per municipality (137 mph for Westerly at Risk Category II). ASCE 7-16 — which RISBC references as the engineered-design standard — defines wind loads as a continuous geographic surface rather than a per-town value.

For any coastal Rhode Island project we:

1. Locate the actual site coordinates from the property deed or survey.
2. Query the ASCE 7-16 Hazard Tool at those coordinates to obtain V_ult for each Risk Category.
3. Design to the higher of the RISBC table value or the ASCE 7-16 Hazard Tool value — the more conservative figure governs.
4. Assess the site's Exposure Category based on actual upwind surface roughness: open water, flat marsh, pasture, woodland, or suburban development within the relevant fetch distance.
5. Apply WBDR requirements when the site is within 1 mile of a qualifying shoreline and V_ult is 130 mph or greater.

This approach ensures that the design reflects the actual wind hazard at the site as determined by the referenced engineering standard, rather than relying on a single per-town lookup value that may not capture local exposure conditions.

Coastal Residential Engineering Services

For Westerly coastal residential projects, our services typically include:

• FEMA floodplain analysis and structural elevation design — elevating the lowest floor above the Base Flood Elevation plus one foot, in compliance with IRC R322 and ASCE 24
• Helical pile foundation design — the preferred deep foundation system for coastal sites with marginal soil bearing or high water tables
• Reinforced concrete grade beam and pier design — spanning between helical piles to support elevated framing
• Shear wall design and uplift connection specification — consistent with ASCE 7-16 wind pressures and the AWC Wood Frame Construction Manual (WFCM) or engineered analysis
• Wind-borne debris region opening specification — coordination with the owner and architect on impact-rated glazing or approved shutter systems
• ASCE 7-16 engineered wind load analysis for structures exceeding the prescriptive thresholds of IRC 2021 R301.2.1.1 or WFCM Chapter 3
• Coordination with FEMA Flood Insurance Rate Map (FIRM) designations — determining A, AE, AO, VE, or Coastal A Zone (LiMWA) requirements at the specific property

Permitting and Regulatory Coordination

Residential projects in Westerly typically navigate four layers of regulatory review:

1. Local zoning — property-line setbacks, height limits, coverage, buffer zones
2. Local building permit — plan review by the building official and the local fire marshal (submitted online)
3. Rhode Island Coastal Resources Management Council (CRMC) — jurisdictional over structures within 200 feet of Mean High Water, within Contiguous Areas of coastal features, and within designated Special Area Management Plan zones. The Salt Ponds Region SAMP covers coastal Westerly including Winnapaug Pond and the Atlantic frontage at Misquamicut and Watch Hill.
4. Rhode Island Department of Environmental Management (RI DEM) — jurisdictional over wetlands, Individual Sewage Disposal System (ISDS) approval, and related environmental review

In our experience, the local Westerly building department handles residential plan review efficiently through a checklist-driven process. The longer lead times on coastal projects come from the state agencies — CRMC review in particular can add several months to the design schedule. Our structural design work can proceed in parallel with the CRMC application rather than waiting on it.

About the Engineer

Frequently Asked Questions

Is my Westerly property in the Wind-Borne Debris Region?

Under the new RISBC (effective December 1, 2025), a Westerly property falls within the Wind-Borne Debris Region (WBDR) when it is within 1 mile of a qualifying coastal shoreline and the applicable Risk Category design wind speed is 130 mph or greater. At Risk Category II (standard residential), Westerly's V_ult is 137 mph — so any single-family residence within 1 mile of the Atlantic coast, Winnapaug Pond, Little Narragansett Bay, or the tidal Pawcatuck River falls within the WBDR. Inland Westerly (Bradford, Potter Hill, Dunn's Corners, Quigley Corner) sits outside the 1-mile zone.

What wind speed does my Westerly home need to be designed to?

The RISBC table publishes a single V_ult of 137 mph for Westerly at Risk Category II — among the highest values in Rhode Island. For engineered design, we use the ASCE 7-16 Hazard Tool at the actual site coordinates and design to the more conservative of the two figures. We also determine the site's Exposure Category based on actual upwind surface roughness: homes within 600 feet of a qualifying coastal shoreline are designed to Exposure Category D; homes further back fall into Exposure C.

Do I need CRMC approval for a coastal Westerly project?

Most coastal Westerly projects fall under Rhode Island Coastal Resources Management Council (CRMC) jurisdiction — particularly any structure within 200 feet of Mean High Water, within the Contiguous Area of a coastal feature (beach, dune, barrier beach, cliff, rocky shore, or salt pond), or within the Salt Ponds Region Special Area Management Plan, which covers coastal Westerly including Winnapaug Pond and the Atlantic frontage at Misquamicut and Watch Hill. CRMC review typically runs in parallel with structural design rather than sequentially.

Adjacent Rhode Island Service Areas

South County Design Group, Inc. provides structural engineering and coastal residential design services across Rhode Island. Explore our other service areas:

• Block Island
• Charlestown
• Jamestown
• Narragansett
• Newport
• North Kingstown
• South Kingstown

Related Engineering Guides

For deeper technical context on the code provisions and engineering frameworks that govern Rhode Island coastal construction:

• FEMA Coastal Flood Zones in Rhode Island — V-Zone and Coastal A Zone foundation requirements, freeboard, and Base Flood Elevation.
• Wind Exposure Categories in Rhode Island — ASCE 7-16 Exposure B, C, and D explained, including the 5,000-foot fetch test.
• Net Zero Engineering for Rhode Island Homes — Integrated modeling for high-performance, all-electric coastal new construction.

Construction Partner

For projects requiring a separately-licensed Rhode Island builder, SCDG coordinates with NJ&J Builders, LLC. For an example coastal Net Zero project SCDG engineered and NJ&J built, see the Built work section of our Net Zero engineering reference.

SCDG and NJ&J Builders, LLC are separately insured and licensed Rhode Island entities operating independently in their respective fields.