GlaziersEdge Knowledge

Sample answers

What SHGC does the 2021 IECC require for commercial glazing in climate zone 2?

Short answer: about 0.25 SHGC for fixed glazing (curtain wall, storefront, fixed windows) and 0.23 for operable windows, for vertical fenestration with a projection factor (PF) under 0.2, on the 2021 IECC commercial prescriptive path.

Things that change the answer

• Overhangs. A larger projection factor allows a higher SHGC; shaded glazing gets more room.
• Code edition. The 2024 IECC tightened some fixed U-factors in colder zones but left the SHGC limits unchanged.
• Compliance path. ASHRAE 90.1 or a performance (energy-model) path can trade glazing performance against other systems.
• Local adoption. States and cities adopt different editions and amend them; always check the jurisdiction.

Climate zone 2 also has a U-factor limit for fixed and operable fenestration; ask the service for the full table by zone.

Ask it yourself

Connect your AI assistant to the free MCP endpoint https://glazing-mcp.glazingkb.workers.dev/mcp (no sign-in) and try:

"What are the 2021 IECC U-factor and SHGC limits for storefront in climate zone 2?"

The full answer comes from the search_glazing_knowledge tool, with section citations and confidence tags. Setup steps: llms.txt.

Last reviewed 2026-10-02.