Two houses in New London can have the same roof, the same modules, and the same racking, and still need different attachment layouts. One is on a tree-lined street a mile from the water. The other looks straight out over the Thames River toward Long Island Sound. The difference is wind exposure, and a New London solar PE stamp has to account for it before the module count is final.
Connecticut's 2022 State Building Code is based on the 2021 International Codes, which use ASCE 7-16 for wind loads. ASCE 7 is where exposure categories, roof zones, and the rooftop solar wind provisions come from. A structural letter that does not name the exposure category is not finished.
Why exposure matters on a New London solar PE stamp
ASCE 7 sorts sites by the roughness of the ground upwind. Most suburban and wooded neighborhoods are Exposure B. Open terrain with scattered obstructions is Exposure C. Exposure D is for flat, unobstructed areas and water surfaces.
The rule that catches coastal jobs is the transition. Under ASCE 7-16, Exposure D applies where that smooth surface prevails upwind for a long distance, and it extends inland into the next exposure for 600 feet or 20 times the building height, whichever is greater. A house on the waterfront, or a few lots back, can sit in Exposure D even though the street looks like a normal neighborhood.
Moving from Exposure B to D raises the design wind pressure on the same roof. Higher pressure means more uplift per attachment, which means closer spacing, more attachments, or a different layout.
Roof zones and edge rows still drive the layout
ASCE 7-16 added specific provisions for rooftop solar panels, including panels installed parallel to the roof surface on buildings of any height and slope. Those provisions use roof zones. Corners and edges see higher suction than the middle of the roof. Panels near the edge of an array also see more load than panels in the middle.
That is why a stamped attachment plan often shows tighter spacing at the perimeter rows and in corner zones. It is not the engineer being cautious. It is the load. On a New London house in Exposure D, the difference between the field spacing and the edge spacing gets larger.
The roof attachment layout post shows how to dimension those zones so an inspector can verify them on the roof.
What the structural letter should state
Athol Energy provides PE stamping and structural review for residential and commercial solar in Connecticut. We are not the installer. We stamp the design and the basis behind it. For a coastal roof, the letter and drawings should state:
- Code basis. The Connecticut State Building Code edition and ASCE 7-16.
- Basic wind speed and risk category. Taken for the exact address, not for the town center.
- Exposure category. With a one-line reason, such as distance to open water.
- Roof framing. Member size, spacing, span, and condition from the site survey.
- Attachment spacing by zone. Field, edge, and corner, matching the racking manufacturer's tested capacity.
- Snow load. Coastal Connecticut carries less snow than the hills, but it is not zero. Check it.
Our posts on structural PE stamps for solar and the New Haven solar PE stamp cover the rest of the letter. New Haven has its own waterfront streets with the same question.
Survey photos that save a revision
The fastest way to get the exposure right is a photo. Ask the site surveyor for one picture looking toward the water from the roof and one from the street. If the reviewer or the engineer can see open water, the Exposure D question is answered before anyone asks it. Add the distance to the shoreline from a map. It takes two minutes.
The electrical side does not care about wind. It does care about the code edition. Connecticut is still on the 2020 NEC, and our post on the NEC edition by state explains why a set borrowed from a Massachusetts job will cite the wrong one.
Questions about coastal solar PE stamps
How do I know if a house is in Exposure D?
Exposure D applies near flat, unobstructed areas and water surfaces. Under ASCE 7-16 it also extends inland 600 feet or 20 times the building height, whichever is greater. The engineer decides based on the site and its distance to open water.
Why do edge rows need more attachments?
Roof edges and corners see higher wind suction, and panels at array edges carry more load. ASCE 7-16's rooftop solar provisions account for both, which usually means tighter spacing at the perimeter.
Which code does Connecticut use for solar wind loads?
Connecticut's 2022 State Building Code is based on the 2021 International Codes, which reference ASCE 7-16 for wind loads.
If you are installing on the Connecticut shoreline this winter, send the site survey with a photo toward the water. Connecticut solar design from Athol Energy will stamp the right exposure. Contact us.