In October 2023 I walked through a sunroom addition in Huntington that had been finished the previous June and had already been abandoned for the summer. The room faced due south with 11 feet of floor-to-ceiling glass. In June, by 10 am, the room was 92°F with the AC running and every ceiling fan on. The homeowner had paid roughly $68,000 for the addition and had not sat in it for three months. The problem was not the AC system. It was a geometry problem, and it was visible on paper before the first post was set.
What orientation actually controls
A south-facing glass wall in the Northeast gets full sun from roughly 9 am to 3 pm in summer, with direct beam hitting the floor and furniture rather than reflecting off the glass. South glass requires precise shading geometry to avoid overheating — a 24-inch roof overhang at Long Island latitudes blocks very little summer sun because the angle is nearly overhead at solstice.
East-facing glass gets direct sun from sunrise until roughly 11 am, then is shaded through the hot afternoon hours. Summer overheating is less severe because morning sun carries less total energy than afternoon sun. The tradeoff is no winter solar gain in the afternoon.
The glazing specifications that matter
Solar heat gain coefficient, or SHGC, is the number on a window label that tells you what fraction of solar energy comes through. A value of 0.60 means 60 percent of incident solar radiation enters as heat. A value of 0.25 means 25 percent does. For a south-facing sunroom on Long Island, an SHGC of 0.25 to 0.30 combined with a deep overhang is a workable design. For an east-facing room that you want warm winter morning sun, 0.40 to 0.50 is more appropriate.
U-factor controls heat loss in winter, not summer gain. A triple-pane unit at U-0.18 loses very little heat on a January night in Huntington, where lows average 22°F to 28°F. U-factor does not protect from June sun.
- SHGC 0.25–0.30 for south-facing glass with limited overhang depth
- SHGC 0.40–0.50 for east-facing glass or south with a properly sized overhang (overhang depth roughly 40 to 50 percent of window height for Long Island latitudes)
- Low-E coating position matters: interior coating (surface 3 or 4) emphasizes U-factor; exterior coating (surface 2) lowers SHGC more aggressively
Overheating correction options once the room is built
If you are working with an existing room that overheats, the options are exterior shading, interior shading, or replacing the glazing. Exterior shading is most effective because it stops radiation before it enters.
- Exterior solar shades or roll-down screens: $300 to $700 per large panel installed. A 10 percent openness fabric blocks about 90 percent of direct solar gain while preserving most of the view.
- A shade structure or extended roof overhang: $2,000 to $8,000 depending on scale. A properly sized overhang at 40 degrees North latitude should extend roughly 50 percent of the window height to shade summer sun and admit winter sun. This is the ideal geometry and it requires a structural engineer if adding to an existing roof line.
- Interior cellular shades: $150 to $400 per window for high-quality cellular units. They reduce summer gain significantly but are less effective than exterior shading because the solar energy has already entered the glass and is heating the room air before the shade reflects it back.
- Glazing replacement: Changing 0.60 SHGC glass to 0.25 SHGC in an existing frame runs $80 to $180 per square foot of glass area for a typical insulated unit, plus labor. On a large sunroom this is a significant cost but may be the only permanent solution.
Sea breeze and winter heating on the North Shore
Huntington faces Long Island Sound. In summer a southwest or south sea breeze develops most afternoons, typically 8 to 15 mph by 2 pm. A sunroom with operable windows on two sides that allows cross-ventilation can use that breeze as a cooling strategy even with high solar gain, if the room is well-vented. Operable skylights or a ridge vent in a cathedral ceiling exhausts the hot air that rises. The stack effect in a well-vented sunroom on a Long Island afternoon can move 300 to 600 CFM without any mechanical equipment.
In January and February the calculus reverses: a south-facing sunroom with low-SHGC glass can contribute meaningful solar gain to the adjacent living space. The Huntington room had that winter potential; the summer overheating erased it. Working with a Long Island sunroom builder at the design stage — before glazing specifications are locked in — is far less expensive than re-glazing afterward.
Frequently asked questions
What is the best window orientation for a sunroom on Long Island? East-facing avoids afternoon summer overheating best. South-facing maximizes winter solar gain but requires a properly sized overhang and low SHGC glass to avoid summer problems. West-facing is generally worst for comfort and energy use in the northeast.
What SHGC should sunroom glass have in the northeast? For south-facing glazing without adequate overhang depth: 0.25 to 0.30. For east-facing or south with a well-designed overhang: 0.35 to 0.50. These values allow useful winter warmth while limiting the worst summer overheating. Check the ENERGY STAR label for your climate zone.
How much does exterior solar shading cost for a sunroom? Exterior roll-down solar screens run $300 to $700 per panel installed, depending on size and motorization. A fixed metal louvre system or extended overhang runs $2,500 to $10,000 for a 12 by 16 foot room. Both are substantially less expensive than replacing the glazing, and exterior shading is more effective per dollar spent.