Optimal South Overhang Depth Analysis for Seasonal Solar Control
A parametric shading study to find the ideal south-facing overhang depth for a residential project in Kansas City, MO — balancing summer solar heat gain reduction with winter passive heating access, using DesignBuilder and EnergyPlus simulation.
Challenge
The client needed a single, continuous horizontal overhang across the south façade — no segmented or vertical shading elements — that would meaningfully cut cooling-season solar heat gain (April–September) without sacrificing the passive heating benefit of low-angle winter sun (October–March).
Approach
GreenBIMSource built a DesignBuilder/EnergyPlus model of the building and ran a parametric sweep of overhang depths from 2 ft to 7 ft in 0.5 ft increments, holding geometry, materials, and window configuration constant. Solar gain was extracted directly from EnergyPlus's Surface Window Transmitted Solar Radiation output for four conditions: full summer, full winter, a peak summer design week, and a cold winter design week — capturing both seasonal totals and extreme-condition performance.
Result
The data showed that most of the summer shading benefit is captured between 2 ft and 4 ft of overhang depth, with diminishing returns beyond that point — while winter solar access declines steadily and more significantly past ~4–5 ft. GreenBIMSource recommended a 3.5 ft continuous overhang, mounted roughly 1 ft above the window head: it cuts full-season summer solar gain by roughly a quarter compared to a minimal 2 ft overhang, while preserving the large majority of winter passive solar gain — a simple, buildable detail backed by simulation data rather than a rule of thumb.
Deliverables
- Parametric solar gain simulation across 11 overhang depths
- Seasonal (full summer/winter) and design-week comparative analysis
- Final overhang depth recommendation with supporting charts
- Summary report for client design decision-making
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