Why Does Solar Heat Gain Matter for Architects and Building Designers?

What Solar Heat Gain Actually Measures

Solar heat gain is the amount of the sun’s energy that passes through glazing and ends up warming the interior ofa building. It’s one of the first things architects and specifiers considerwhen balancing daylight, comfort, and energy use on a facade, and it’s central to how eLstar Dynamics approaches glazing design.

Every window, curtain wall panel, or skylight has a rating for this, expressed as SHGC (Solar Heat Gain Coefficient) in the US, or g-value under the European standard EN 410. Both describe the same underlying property: the fraction of solar radiation that makes it through the glass, whether transmitted directly or absorbed and re-released as heat.

A lower number means less heat gets through. A g-value of 0.25 to 0.40 offers strong solar protection, suited to south-facing facades or large glazed surfaces. Higher values let more solar heat in, which can help offset heating loads in colder climates.

Why Codes and Certifications Put a Number on It

This isn’t just a design preference. ASHRAE 90.1, the US energy standard underlying most commercial building codes, sets maximum SHGC limits by climate zone as mandatory minimums, not aspirational targets, and requirements scale with climate: hotter zones emphasize SHGC limits to control solar heat gain, while colder zones balance SHGC against insulation and heating demand, as summarized in National Glass Association technical guidance on US energy conservation codes.

In Europe, the g-value is determined per EN 410 and typically paired with U-value (thermal transmittance) for a complete picture of a facade’s thermal behavior. The two pull in different directions by design: U-value governs heat lost through the glazing, g-value governs heat gained. Balancing both for a specific facade, not just hitting one number, is the real design problem.

The Specifier’s Balancing Act

A very low SHGC or g-value blocks heat effectively, but it also cuts visible light transmission and gives up useful solar gain in winter. That tradeoff plays out differently by orientation and climate. A south-facing facade in a hot climate benefits from aggressive solar control; a north-facing facade, or one in a colder climate wanting passive winter heating, can often use a higher value without a comfort or energy penalty.

This is why blanket specifications, one value for every facade on a building, tend to underperform. A building with varied solar exposure usually needs different glazing specifications section by section, not a single number applied uniformly.

Where a Fixed Value Runs Into Limits

The core limitation of any static glazing spec is that SHGC and g-value are fixed at manufacture. A facade optimized for winter passive solar gain will tend to overheat in summer; one optimized for summer heat rejection gives up free winter heating it could have used.

Shading devices, like blinds, louvers, or overhangs, are the traditional fix, letting a building shift its effective solar heat gain across the day or season, at the cost of a mechanical system with its own upkeep. Dynamic glazing takes a different approach: rather than adding a shading layer, the glazing itself can be designed to change its solar heat gain properties in response to conditions. That’s the premise behind eclipse™, eLstar Dynamics’ dynamic glass built on ELM (Electrophoretic Light Modulation) technology. See how ELM technology works for a closer look at the mechanism.

One practical note for certification-tracked projects: simplified compliance calculations built for static glazing, like the sDA/ASE simulation pathway used for LEED’s Daylight credit, don’t accept dynamic facades or electrochromic glass without extra work. Dynamic elements need to be pre-simulated to determine their effective visual transmittance before they can be used in a standard compliance calculation, according to LEED daylighting documentation from energy modeling platform cove.tool. In practice, that means bringing in a daylight modeling specialist earlier than a project using static glass and blinds would.

Where This Fits Into a Specification

None of this means dynamic glazing is the right call for every facade. A single-orientation building in a mild climate may do perfectly well with a well-chosen static SHGC or g-value and conventional shading. The calculation changes once a facade faces significant seasonal swings, mixed orientations, or a certification target that rewards adaptive daylight and glare control.

That’s the gap eclipse™ smart glass is built to close: rather than locking in one SHGC or g-value for the life of the building, it adjusts in response to conditions. For a deeper look at where that fits in a project, see our Architects page or get in touch with the eLstar Dynamics team about your questions regarding specific facade needs.

Where eclipse™ glazing fits

eLstar Dynamics’ ELM technology is designed so that a facade’s effective solar heat gain isn’t locked in at manufacture. Because transmission can be modulated continuously rather than fixed to a single SHGC or g-value, the same glazing can behave more like a low-SHGC spec during peak summer sun and more like a higher-SHGC spec during a mild or overcast period, without a separate mechanical shading system. The certification documentation implications described above (pre-simulation for LEED’s daylight credit) apply to dynamic glazing broadly, including eclipse™, so this is worth planning for early in a certification-tracked project.

F.A.Q.

Is a lower SHGC or g-value always better? No. It depends on climate and orientation. A very low value is usually right for a south or west-facing facade in a hot climate, but the same value on a north-facing facade in a colder climate gives up useful winter solar heating for no real comfort benefit.

Why does dynamic glazing need extra documentation for certification credits? Because most compliance calculations, including LEED’s simplified daylight simulation pathway, were built around glazing with a single fixed SHGC or g-value. Dynamic glazing changes that value throughout the day, so it needs to be pre-simulated separately to establish its effective performance before it can be used in a standard compliance calculation.

Talk to us about your facade

Every facade has its own mix of orientation, climate exposure, and certification targets to balance. If you’re weighing static glazing against a dynamic solution for a specific project, get in touch with eLstar Dynamics to talk through the specifics, or visit our Architects page to see how eclipse™ glazing fits into facade design more broadly.