From this site

One project, every trade

Each calculator adds its lines to a single estimate — consolidated BOM, schedule and cash-flow included.

Open My Project →

SHGC Effective Shading Fraction Calculator

Calculate the effective solar heat gain coefficient of a window with a fixed horizontal overhang, accounting for the shadow it casts.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax
4.92 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

Effective SHGC

0.15 SHGC

Check your inputs

This simplified geometric approximation is for a window facing directly toward the sun (zero azimuth difference) and treats shaded glass as receiving negligible direct gain, which overstates shading benefit since diffuse/reflected radiation still reaches shaded glass. For precise energy modeling, use ASHRAE 90.1/LBNL Projection Factor tables or full solar gain software.

Shaded fraction of window
0.63

For the dimensions entered, expect a effective shgc of 0.15. Moderate confidence — sound arithmetic, but allow for the variation any real site introduces. Set for United States against IRC 2024. The market selector changes both the units and the code cited.

Add the equipment this sizes

This result is a specification — 0.15 SHGC — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • ASHRAE profile-angle method (Fundamentals Ch. 15): shadow drop on the glass = overhang projection × tan(solar altitude angle) [for a window facing directly into the sun]; shaded fraction = clamp((shadow drop − head gap) ÷ window height, 0, 1); a common simplified approximation is effective SHGC ≈ glass SHGC × (1 − shaded fraction), treating shaded glass as receiving negligible direct gain

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Frequently asked questions

Why does a higher solar altitude angle reduce effective SHGC?
A higher solar altitude angle means the sun is more directly overhead, so the shadow cast by a fixed horizontal overhang drops further down the window and covers more of the glass — increasing the shaded fraction and lowering the effective SHGC.
Does this account for the sun's horizontal (azimuth) angle?
No — this calculation assumes the window faces directly into the sun with no azimuth offset. A window facing away from the sun's compass direction receives a longer effective shadow than this simplified vertical-drop method predicts.
Is shaded glass treated as receiving zero solar gain?
Effectively yes in this approximation — it assumes shaded glass contributes negligible direct solar gain, which understates actual heat gain since diffuse sky radiation and ground-reflected radiation still reach shaded glass. Use full solar gain software for a precise energy calculation.