BLIND SOLUTIONS
Skylight Assessment Tool — Cheat Sheet
Quick-reference cheat sheet for the Skylight Assessment Tool tool.
Published 27 May 2026
CHEAT SHEET
Skylight Assessment Tool
Quick-reference companion for the free Portal tool
What This Tool Does
The Skylight Assessment Tool on the Blind Solutions Architects Portal is designed to assist South African architects in evaluating the thermal performance and daylighting potential of skylights in their building designs. It helps ensure compliance with relevant SANS regulations (e.g., SANS 10400-XA for energy efficiency) and informs decisions regarding glazing specifications, shading, and overall building energy consumption.
Use this tool during the early design stages to compare different skylight options, optimize their placement, and predict their impact on internal comfort and energy loads. It's essential for any project aiming for energy-efficient design, Green Star SA certification, or simply looking to harness natural light effectively without compromising thermal performance.
Step-by-Step Usage Guide
Step 1: Project & Location Details
Input your project's geographical coordinates (e.g., Latitude: -26.2041, Longitude: 28.0473 for Johannesburg). Select the relevant South African climate zone (e.g., "Zone 2: Highveld Interior" for Johannesburg). This data is crucial for accurate solar radiation calculations.
Input your project's geographical coordinates (e.g., Latitude: -26.2041, Longitude: 28.0473 for Johannesburg). Select the relevant South African climate zone (e.g., "Zone 2: Highveld Interior" for Johannesburg). This data is crucial for accurate solar radiation calculations.
Step 2: Skylight Geometry & Orientation
Define the skylight's dimensions (e.g., 1.2m x 1.2m square), its tilt angle (e.g., 15 degrees from horizontal), and its cardinal orientation (e.g., "North" for maximum winter solar gain, or "South" for more diffused light). Specify the roof pitch if it's integrated.
Define the skylight's dimensions (e.g., 1.2m x 1.2m square), its tilt angle (e.g., 15 degrees from horizontal), and its cardinal orientation (e.g., "North" for maximum winter solar gain, or "South" for more diffused light). Specify the roof pitch if it's integrated.
Step 3: Glazing Specification
Select your glazing type. Common options include:
Select your glazing type. Common options include:
- Single Glazing (e.g., 6mm Clear Float) - U-Value ≈ 5.8 W/m²K, SHGC ≈ 0.85
- Double Glazing (e.g., 6mm Clear + 12mm Air Gap + 6mm Clear) - U-Value ≈ 2.8 W/m²K, SHGC ≈ 0.75
- High-Performance Double Glazing (e.g., Low-E coating, Argon fill) - U-Value ≈ 1.8 W/m²K, SHGC ≈ 0.40
Step 4: Shading & Obstructions
Indicate if any internal or external shading devices are used (e.g., blinds, external louvres). Specify their SHGC reduction factor if known. Also, account for any external obstructions (e.g., adjacent buildings, trees) that might cast shadows at certain times of the day or year.
Indicate if any internal or external shading devices are used (e.g., blinds, external louvres). Specify their SHGC reduction factor if known. Also, account for any external obstructions (e.g., adjacent buildings, trees) that might cast shadows at certain times of the day or year.
Step 5: Internal Conditions & Usage
Set the desired internal temperature ranges for heating and cooling seasons, and specify typical occupancy hours. This helps evaluate comfort and energy impact relative to user expectations. For example, a commercial office might target 20-24°C during business hours.
Set the desired internal temperature ranges for heating and cooling seasons, and specify typical occupancy hours. This helps evaluate comfort and energy impact relative to user expectations. For example, a commercial office might target 20-24°C during business hours.
Step 6: Generate & Interpret Report
Click "Generate Report". The tool will provide estimated daylighting levels (e.g., lux levels at working plane), annual solar heat gain, and heat loss through the skylight. It will also offer a preliminary assessment against SANS 10400-XA requirements for the specified climate zone.
Click "Generate Report". The tool will provide estimated daylighting levels (e.g., lux levels at working plane), annual solar heat gain, and heat loss through the skylight. It will also offer a preliminary assessment against SANS 10400-XA requirements for the specified climate zone.
Common Scenarios & Expected Results
| Scenario | Input | Expected Output |
|---|---|---|
| Highveld Office, Winter Daylighting | Johannesburg (Zone 2), North-facing 1.5m x 1.5m skylight, Double Glazing (U=2.8, SHGC=0.75), Midday in June. | High daylight levels (e.g., 800-1200 lux) directly below skylight. Significant solar heat gain, potentially reducing heating demand. Low heat loss. |
| Coastal Residence, Summer Overheating | Durban (Zone 1), West-facing 1m x 2m skylight, Single Glazing (U=5.8, SHGC=0.85), Mid-afternoon in January. | Very high solar heat gain, likely leading to overheating. Uncomfortably bright light. High heat loss at night. Tool recommends high-performance glazing or external shading. |
| Warehouse, Diffused Light | Cape Town (Zone 3), South-facing 2m x 2m skylight, Translucent/Opal Double Glazing (U=2.5, SHGC=0.50), No direct sun. | Good, even diffused daylight (e.g., 400-600 lux). Moderate solar heat gain. Reduced glare compared to clear glazing. |
| Energy-Efficient Design, SANS-X Compliance | Pretoria (Zone 2), East-facing 1m x 1m skylight, Low-E Double Glazing (U=1.8, SHGC=0.40), External Louvres. | Optimised balance of daylight and thermal performance. Meets or exceeds SANS 10400-XA requirements. Controlled solar heat gain, reduced heat loss. |
Pro Tips
South African Climate Zones: Always select the correct climate zone. SANS 10400-XA divides SA into six zones, each with unique thermal performance requirements. Misidentifying your zone can lead to non-compliance or suboptimal design.
Beyond U-Value: Don't just focus on U-Value for thermal performance. The Solar Heat Gain Coefficient (SHGC) is equally critical, especially in sunny South Africa. A low SHGC minimizes unwanted solar heat gain in summer, reducing cooling loads.
External Shading is King: For skylights, external shading (e.g., fixed louvres, external blinds) is far more effective at preventing solar heat gain than internal shading. Model different external shading options to find the optimal balance.
Daylight Autonomy vs. Overlighting: Aim for adequate daylight autonomy (the percentage of occupied hours when daylight alone can provide sufficient illumination) without causing overlighting, which can lead to glare and excessive heat gain. Use the tool to balance these.