BLIND SOLUTIONS
Fabric Openness Calculator — Cheat Sheet
Quick-reference cheat sheet for the Fabric Openness Calculator tool.
Published 27 May 2026
CHEAT SHEET
Fabric Openness Calculator
Quick-reference companion for the free Portal tool
What This Tool Does
The Fabric Openness Calculator is an essential tool for South African architects using the Blind Solutions Architects Portal. It helps you accurately determine the optimal openness factor for various blind and shading fabrics based on specific project requirements, environmental conditions, and desired performance outcomes. This ensures compliance with SANS 10400-XA energy efficiency regulations and enhances occupant comfort.
Use this calculator early in the design process when specifying internal or external shading solutions for commercial, residential, or public buildings. It's crucial for projects aiming for Green Star SA certification, or any design where solar heat gain, glare control, and natural daylighting are critical considerations. Architects, façade consultants, and sustainable design specialists will find this tool invaluable for informed material selection.
Step-by-Step Usage Guide
Step 1: Project Location & Orientation
Enter the precise geographical coordinates for your project site. For example, for a typical Johannesburg CBD project, input "Latitude: -26.2041" and "Longitude: 28.0473". Specify the building's primary façade orientation (e.g., "North", "East", "West", "South") as this significantly impacts solar exposure.
Enter the precise geographical coordinates for your project site. For example, for a typical Johannesburg CBD project, input "Latitude: -26.2041" and "Longitude: 28.0473". Specify the building's primary façade orientation (e.g., "North", "East", "West", "South") as this significantly impacts solar exposure.
Step 2: Glazing Specifications
Provide detailed information about the glazing system. This includes the U-value (e.g., "3.5 W/m²K" for standard clear glass), Solar Heat Gain Coefficient (SHGC) (e.g., "0.75" for clear single glazing), and Visible Light Transmittance (VLT) (e.g., "0.85"). Accurate glazing data is vital for precise solar gain calculations.
Provide detailed information about the glazing system. This includes the U-value (e.g., "3.5 W/m²K" for standard clear glass), Solar Heat Gain Coefficient (SHGC) (e.g., "0.75" for clear single glazing), and Visible Light Transmittance (VLT) (e.g., "0.85"). Accurate glazing data is vital for precise solar gain calculations.
Step 3: Desired Performance Criteria
Define your primary performance objectives. Are you prioritizing maximum daylighting with minimal glare, or aggressive heat gain reduction? Select from options like "Glare Control (High)", "Heat Reduction (Medium)", "Daylight Optimisation (High)". This informs the calculator's recommendations for openness factors.
Define your primary performance objectives. Are you prioritizing maximum daylighting with minimal glare, or aggressive heat gain reduction? Select from options like "Glare Control (High)", "Heat Reduction (Medium)", "Daylight Optimisation (High)". This informs the calculator's recommendations for openness factors.
Step 4: Internal vs. External Shading
Indicate whether the shading solution will be installed internally or externally. External shading is generally more effective at preventing solar heat gain, while internal shading offers more flexibility for glare control. This choice impacts the required openness factor for optimal performance.
Indicate whether the shading solution will be installed internally or externally. External shading is generally more effective at preventing solar heat gain, while internal shading offers more flexibility for glare control. This choice impacts the required openness factor for optimal performance.
Step 5: Review & Interpret Results
The calculator will provide a recommended range of openness factors (e.g., "3% - 5%") along with an explanation of the thermal and visual performance characteristics for fabrics within that range. It may also suggest specific Blind Solutions fabric types that meet these criteria.
The calculator will provide a recommended range of openness factors (e.g., "3% - 5%") along with an explanation of the thermal and visual performance characteristics for fabrics within that range. It may also suggest specific Blind Solutions fabric types that meet these criteria.
Step 6: Refine & Compare
Experiment with different inputs (e.g., varying desired performance or glazing types) to understand how changes impact the recommended openness. Use this to compare different fabric options and make an informed decision for your project.
Experiment with different inputs (e.g., varying desired performance or glazing types) to understand how changes impact the recommended openness. Use this to compare different fabric options and make an informed decision for your project.
Common Scenarios & Expected Results
| Scenario | Input | Expected Output |
|---|---|---|
| High Glare Control (Office) | Location: Cape Town (Latitude: -33.9249, Longitude: 18.4241) Orientation: West Façade Glazing: SHGC 0.65, VLT 0.80 Performance: Glare Control (High) Shading: Internal |
Recommended Openness: 1% - 3% (Minimises direct glare, maintains some view out. Suggests denser weave fabrics.) |
| Heat Reduction (Residential) | Location: Durban (Latitude: -29.8587, Longitude: 31.0218) Orientation: North Façade Glazing: SHGC 0.70, VLT 0.82 Performance: Heat Reduction (Medium) Shading: External |
Recommended Openness: 5% - 7% (Effective solar heat rejection, good daylighting. Suggests medium-density external screen fabrics.) |
| Daylight Optimisation (School) | Location: Pretoria (Latitude: -25.7479, Longitude: 28.2293) Orientation: East Façade Glazing: SHGC 0.72, VLT 0.85 Performance: Daylight Optimisation (High) Shading: Internal |
Recommended Openness: 7% - 10% (Maximises natural light, softer glare diffusion. Suggests lighter, more open weave fabrics.) |
| SANS 10400-XA Compliance (Commercial) | Location: Polokwane (Latitude: -23.9045, Longitude: 29.4674) Orientation: North-West Façade Glazing: Low-E Double Glazing (SHGC 0.35, VLT 0.60) Performance: Heat Reduction (High), Glare Control (Medium) Shading: Internal |
Recommended Openness: 3% - 5% (Balances heat gain with visual comfort, often required for energy efficiency targets with good glazing.) |
Pro Tips
Combine with External Shading: For facades with high solar exposure (e.g., North and West in SA), consider external shading solutions first. They are significantly more effective at preventing heat gain. Use the calculator to fine-tune the internal blind openness for residual glare control or privacy.
Climate Zone Considerations: Remember that South Africa has diverse climate zones. A low openness factor might be crucial in hot, arid regions like Upington for heat rejection, while a higher openness might be acceptable in cooler, temperate zones like the Garden Route for daylighting. Always cross-reference with SANS 10400-XA climate zone requirements.
Daylight Autonomy vs. Glare: Achieving high daylight autonomy is excellent, but don't compromise on visual comfort. A too-high openness factor on a sunny façade will lead to excessive glare. Balance these two by iteratively adjusting the desired performance criteria in the calculator.
Material Colour Matters: While the calculator focuses on openness, remember that fabric colour also impacts performance. Lighter colours reflect more solar radiation, reducing heat gain, but can increase reflected glare. Darker colours absorb more heat but offer better view-through and glare control.