Commercial Building Inspector B2Building EnclosureMedium
An inspector is reviewing the specifications for a new curtain wall system on a commercial high-rise. The design calls for a glass with a Solar Heat Gain Coefficient (SHGC) of 0.25. According to the IBC and IECC, what does an SHGC value of 0.25 indicate regarding the fenestration's performance?
- AThe fenestration allows 25% of the visible light to pass through.
- BThe fenestration's thermal resistance (R-value) is 0.25.
- CThe fenestration prevents 75% of the solar heat from entering the building.
- DThe fenestration has a U-factor of 0.25.
Show answer & explanationAnswer & explanation
Correct answer: C. The fenestration prevents 75% of the solar heat from entering the building.
The Solar Heat Gain Coefficient (SHGC) represents the fraction of incident solar radiation admitted through a window, both directly transmitted and absorbed and subsequently released inward. An SHGC of 0.25 means that 25% of the solar heat is allowed to pass through, and consequently, 75% is blocked or rejected.
Why the other options are wrong
- A. This describes Visible Transmittance (VT), not SHGC.
- B. R-value is the inverse of U-factor and measures thermal resistance, not solar heat gain directly.
- D. U-factor measures heat loss/gain due to temperature difference, not solar radiation.
Solar Heat Gain Coefficient (SHGC)
A measure of how much solar radiation (heat) is admitted through a window, door, or skylight.
- Expressed as a number between 0 and 1.
- Lower SHGC values indicate less solar heat gain.
- Important for controlling cooling loads in buildings.
Memory trick: SHGC: Solar Heat Gets Cooled.