Shading Calculator

Quick-reference companion for the free Portal tool

What This Tool Does

The Blind Solutions Shading Calculator is an essential tool for South African architects to accurately assess the impact of external shading devices on solar heat gain and daylighting performance. It helps you design energy-efficient buildings that comply with SANS 10400-XA energy efficiency requirements, specifically regarding fenestration. By simulating various shading configurations, you can optimize for thermal comfort, reduce cooling loads, and maximize natural light while mitigating glare.

Use this tool during the early design stages to inform façade design, window sizing, and shading device selection. It's crucial for projects aiming for Green Star SA accreditation or any project where occupant comfort and operational energy savings are priorities. It's particularly useful for high-performance glazing specifications, ensuring that your choice of glass works symbiotically with your shading strategy.

This calculator is designed for architects, façade consultants, and sustainable design professionals working on residential, commercial, and institutional projects across South Africa's diverse climate zones.

Step-by-Step Usage Guide

Step 1: Project Location & Orientation

Input your project's precise geographical coordinates and true north orientation. This is critical for accurate solar path calculations. For Johannesburg, you'd typically use Latitude: -26.2041° S, Longitude: 28.0473° E. For other regions, consult your site survey or Google Maps. Ensure your building's orientation (e.g., 0° for North-facing façade, 90° for East) is correctly entered relative to true north.

Step 2: Window/Glazing Specifications

Define the characteristics of your window opening. This includes its width, height, and sill height from the finished floor level. Also, input the U-value (W/m²K) and Solar Heat Gain Coefficient (SHGC) of your chosen glazing. Typical South African double glazing might have a U-value of 2.0-2.5 and an SHGC of 0.3-0.5. For single glazing, expect U-values around 5.7 and SHGCs of 0.7-0.8.

Step 3: Shading Device Definition

Select the type of external shading you wish to analyze (e.g., horizontal overhang, vertical fins, egg-crate). Input its specific dimensions: projection length, height, depth, and distance from the window plane. For a simple horizontal overhang, you might input a projection of 900mm from the window plane, 100mm thick, placed 100mm above the window head.

Step 4: Time and Date Selection

Choose the specific date and time of day you want to analyze. This allows you to assess performance during critical periods, such as peak summer afternoons (e.g., December 21st, 14:00) or winter mornings (e.g., June 21st, 09:00). You can also run simulations for an entire year to get an annual profile.

Step 5: Run Calculation & Interpret Results

Click "Calculate" to generate the shading analysis. The tool will display the percentage of the window shaded at the specified time, the Effective SHGC (SHGC_eff) of the shaded window, and often a visual representation of the sun's path and shadow cast. A lower SHGC_eff indicates better solar heat gain control. Compare these results against SANS 10400-XA requirements for your climate zone.

Common Scenarios & Expected Results

Scenario	Input (Example for Johannesburg: -26.2° S, 28.0° E)	Expected Output
North-facing Window, No Shading (Summer)	Window: 1.5m W x 2.1m H, Sill 0.9m. Orientation: 0° (North). Date: Dec 21st, 12:00.	Window 100% in direct sun. High SHGC_eff (e.g., 0.6-0.8 depending on glazing). Significant solar heat gain.
North-facing Window, Effective Horizontal Overhang (Summer)	Same as above + Horizontal Overhang: 900mm projection, 100mm thick, 100mm above window head.	Window 80-100% shaded. Significantly reduced SHGC_eff (e.g., 0.1-0.3). Good solar control.
West-facing Window, No Shading (Summer PM)	Window: 1.5m W x 2.1m H, Sill 0.9m. Orientation: 270° (West). Date: Dec 21st, 16:00.	Window 100% in direct sun. Very high SHGC_eff. Severe glare and overheating.
West-facing Window, Vertical Fins (Summer PM)	Same as above + Vertical Fins: 300mm projection, 100mm thick, 450mm spacing.	Window 50-70% shaded. Reduced SHGC_eff (e.g., 0.3-0.5). Improved but still challenging solar control. Requires careful design.

Pro Tips

Master the Sun Path

Understand the sun's path for your specific location and orientation. In South Africa, the sun is generally to the North. North-facing windows benefit most from horizontal shading in summer, while East and West facades require vertical or egg-crate solutions to combat low-angle sun. South-facing windows typically receive minimal direct sun.

Iterate and Compare

Don't settle for the first design. Utilize the calculator to test multiple shading device types, dimensions, and positions. Compare the resulting SHGC_eff values against your target performance criteria and SANS 10400-XA requirements. A small adjustment can sometimes yield significant energy savings.

Consider Annual Performance

While summer peak analysis is crucial for cooling, also check winter performance (e.g., June 21st, 10:00). Ensure your shading doesn't excessively block desirable winter sun, leading to increased heating loads. A good design balances summer shading with winter solar gain.

Beyond External Shading

Remember that external shading is one part of a holistic façade strategy. Pair effective external shading with high-performance glazing, appropriate window-to-wall ratios, and consider internal shading (like blinds) for glare control and added insulation. The calculator focuses on external elements but informs the overall strategy.

🔧 OPEN SHADING CALCULATOR