Structural Engineer Serving Narragansett, 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 Narragansett and the surrounding southern 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 Narragansett 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.

Narragansett 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 Narragansett, followed by how we translate them to a specific property.

Narragansett · RISBC Design Parameters

Parameter	Value
Ground snow load	30 psf
Flat roof snow load	30 psf
Ultimate design wind speed (Vult), Risk Category I	121 mph
Ultimate design wind speed (Vult), Risk Category II	131 mph # — WBDR applies within 1 mile of coast
Vult, Risk Category III	140 mph *
Vult, Risk Category IV	143 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 Narragansett

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) exceeds 130 mph; and
2. The structure is within 1 mile of the "mean high coastal water line."

For Narragansett at Risk Category II, V_ult is 131 mph — 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.

What Counts as "Coastal" in Narragansett

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 Narragansett, this interpretation identifies the qualifying shorelines as:

• The open Atlantic coast — along Scarborough State Beach, Narragansett Town Beach, Narragansett Pier, and the Galilee / Point Judith area
• Point Judith Pond — a large tidal pond with extensive fetch
• Narragansett Bay — along the town's eastern frontage south of Saunderstown
• The Pettaquamscutt River (Narrow River) — along the town's western frontage; fetch varies by reach

Inland Narragansett — the northern and central residential neighborhoods away from the ocean and river — generally sits outside the qualifying-shoreline framework. Structures in those interior areas typically fall into Exposure C.

For a full plain-English explanation of how Exposure Categories B, C, and D work in Rhode Island, see Understanding Wind Exposure Categories in Rhode Island.

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 Narragansett 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 along Ocean Road, Scarborough, Bonnet Shores, and Point Judith 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 Narragansett — the northern and central residential neighborhoods away from the ocean, Point Judith Pond, the Bay, and the Narrow River — sits outside both zones.

How We Determine Wind Load for a Specific Narragansett Site

The RISBC publishes a single V_ult value per municipality (131 mph for Narragansett 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 exceeds 130 mph.

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 Narragansett 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 Narragansett 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 Narrow River Special Area Management Plan covers the Pettaquamscutt River (Narrow River) portion of coastal Narragansett.
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 longer lead times on coastal Narragansett 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 Narragansett property in the Wind-Borne Debris Region?

Under the new RISBC (effective December 1, 2025), a Narragansett 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 (V_ult) exceeds 130 mph. At Risk Category II (standard residential), Narragansett's V_ult is 131 mph — so any single-family residence within 1 mile of the Atlantic coast, Point Judith Pond, Narragansett Bay, or the tidal Narrow River falls within the WBDR. Inland Narragansett away from these waters sits outside the 1-mile zone.

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

The RISBC table publishes a single V_ult of 131 mph for Narragansett at Risk Category II. For engineered design, we use the ASCE 7-16 Hazard Tool at the actual site coordinates — which can produce a higher value at specific coastal locations — 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 (the highest wind exposure); homes further back fall into Exposure C.

Do I need CRMC approval for a coastal Narragansett project?

Most coastal Narragansett 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 a designated Special Area Management Plan. The Narrow River Special Area Management Plan and the Metropolitan Bay Region SAMP cover coastal Narragansett jurisdictional waters. CRMC review typically runs in parallel with structural design rather than sequentially. Our engineering documents are prepared to coordinate with the CRMC application package.