Structural Engineer Serving Jamestown, 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 Jamestown and the surrounding Narragansett Bay islands. 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 Jamestown 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.

Jamestown 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 Jamestown, followed by how we translate them to a specific property. Jamestown is an entire town on a single island (Conanicut Island) — an unusual geography that has direct consequences for how the code's coastal provisions apply.

Jamestown · RISBC Design Parameters

Parameter	Value
Ground snow load	30 psf
Flat roof snow load	30 psf
Ultimate design wind speed (Vult), Risk Category I	108 mph
Vult, Risk Category II	121 mph — see note below on ASCE 7-16 Hazard Tool values at coastal coordinates
Vult, Risk Category III	131 mph # — WBDR applies within 1 mile of coast
Vult, Risk Category IV	139 mph #
Frost depth (residential, RISBC-2)	3'-4"
Frost depth (commercial, RISBC-1)	4'-0"
Winter design temperature (Newport 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 Jamestown

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."

A Jamestown-Specific Note on the Table Value vs. the Hazard Tool

The RISBC Table R301.2(5) value for Jamestown at Risk Category II is 121 mph — about 10 mph below every neighboring coastal municipality, and below the 130 mph Wind-Borne Debris Region threshold. The ASCE 7-16 Hazard Tool, queried at coastal Jamestown coordinates (Beaver Tail, the village frontage, the East and West Passage shorelines), returns 130 mph at Risk Category II — consistent with what the same tool returns at Newport, Narragansett, and Middletown.

In our practice, we design to the higher of the RISBC table value or the ASCE 7-16 Hazard Tool value at the actual site. For coastal Jamestown projects this places the structure within the Wind-Borne Debris Region under the referenced engineering standard, and we design accordingly with impact-rated openings.

The Jamestown table value at Risk Category II is currently being evaluated. For engineered design we defer to ASCE 7-16 — the standard the Rhode Island State Building Code references — applied at the actual site coordinates.

What Counts as "Coastal" in Jamestown

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 Jamestown, this interpretation identifies the qualifying shorelines as:

• The open Atlantic coast / East Passage — along the south end at Beaver Tail State Park, Fort Wetherill, and Mackerel Cove
• The East Passage of Narragansett Bay — Jamestown's eastern frontage
• The West Passage of Narragansett Bay — Jamestown's western frontage (Dutch Island Harbor and along the bay's western shore)

Jamestown is essentially an island with water exposure on all sides. Truly "inland" Jamestown sites — more than 600 feet from Exposure D shoreline in all directions — are rare.

For deeper context, our published references cover ASCE 7-16 wind exposure categories as applied to Rhode Island sites, 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

Because Conanicut Island is roughly 9 miles long and at most about 1.5 miles wide, nearly every building site on the island is within 1 mile of at least one qualifying shoreline. A typical Jamestown residence sits within all three concentric zones — within 600 feet of open water (Exposure D), within 1 mile of the coast (WBDR under the ASCE 7-16 Hazard Tool value), and designed to a V_ult at or above 130 mph.

How We Determine Wind Load for a Specific Jamestown Site

The RISBC publishes a single V_ult value per municipality (121 mph for Jamestown 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, and at coastal Jamestown coordinates produces 130 mph.

For any coastal Jamestown 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 referenced engineering standard produces V_ult values at or above 130 mph and the site is within 1 mile of a qualifying shoreline.

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, in Jamestown's case, understates the engineered design wind speed at coastal coordinates.

Coastal Residential Engineering Services

For Jamestown 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 Jamestown 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
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. Jamestown is not within a place-based CRMC Special Area Management Plan; coastal projects are reviewed under CRMC's general Coastal Resources Management Program (the "Red Book"), with the statewide Shoreline Change (Beach) SAMP applied as a climate/erosion overlay. Because Jamestown is an island town, CRMC review applies to nearly all coastal-fronting projects.
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 Jamestown projects come from the state agencies — CRMC review in particular can add several months to the design schedule given the island's essentially all-coastal character. 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 Jamestown property in the Wind-Borne Debris Region?

Under the new RISBC (effective December 1, 2025), the Table R301.2(5) value for Jamestown at Risk Category II is 121 mph — below the 130 mph WBDR threshold as strictly published. However, in our practice we use the ASCE 7-16 Hazard Tool at actual site coordinates rather than relying solely on the per-town lookup table. The ASCE 7-16 Hazard Tool produces 130 mph at coastal Jamestown locations, which places those sites within the WBDR under the referenced engineering standard. For Jamestown coastal-fronting residences — nearly all of Conanicut Island given the town's geography — we design to the WBDR requirements.

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

The RISBC table publishes a single V_ult of 121 mph for Jamestown at Risk Category II. For engineered design, we use the ASCE 7-16 Hazard Tool at the actual site coordinates — which at coastal Jamestown produces 130 mph — and design to the higher value. We also determine the site's Exposure Category based on actual upwind surface roughness: most of Jamestown's coastal-facing sites fall within 600 feet of a qualifying shoreline and are designed to Exposure Category D.

Do I need CRMC approval for a coastal Jamestown project?

Most coastal Jamestown 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 an applicable Special Area Management Plan. Jamestown is not within a place-based CRMC Special Area Management Plan; coastal projects are reviewed under CRMC's general Coastal Resources Management Program (the "Red Book"), with the statewide Shoreline Change (Beach) SAMP applied as a climate/erosion overlay. Because Jamestown is an island town, CRMC review applies to nearly all coastal-fronting projects. CRMC review typically runs in parallel with structural design rather than sequentially. Our engineering documents are prepared to coordinate with the CRMC application package.

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
• Narragansett
• Newport
• North Kingstown
• South Kingstown
• Westerly

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.