With rising temperatures and increasing electricity costs day by day, today every building needs to be designed for better thermal performance and energy efficiency. In the hot climates of India, the roof can contribute 25 to 35% of total heat gain in the buildings. This increases indoor temperature and puts extra load on air conditioning systems, which already consume 40-60% of total electricity in large buildings. One of the most effective ways to reduce this heat absorption is by using heat reflective coatings, which are also known as cool roof coatings. These coatings can reduce roof surface temperature by 20–40°C, lower the indoor temperature by 2–5°C, and reduce the HVAC energy use by 10–30%.
However, Architects should not choose heat reflective coatings based on color or brand name. The most important things to check are SRI and ASTM-tested performance values. These numbers show how well the coating reflects heat and performs over time. Understanding these terms helps the architects to choose the right heat reflective coating and improve the energy performance.
Here, in this blog, we will provide a complete guide on Specifying Heat Reflective Coatings: What Architects Need To Know About SRI & ASTM.
What is Heat Reflective Coating?
Heat reflective coating is a special coating that is applied to roofs to reflect sunlight and release heat quickly. It helps to reduce the roof temperature and prevents heat from entering the buildings, and makes the inside cooler. These cool roof coatings are commonly used on RCC roofs, Metal roofs, Industrial sheets, warehouses, commercial buildings, and other industrial facilities.
The heat reflective paint mainly works on two principles: Solar Reflectance, which reflects the sunlight away from the roof and Thermal Emittance, which releases the heat that the roof absorbs. When both solar reflectance and thermal emittance are high, the roof stays much cooler as compared ot a normal roof.
Benefits of Heat Reflective Coating:
- Lower roof temperature.
- Reduced indoor temperature.
- Lower HVAC energy consumption
- Reduced electricity bills
- Improves thermal comfort
- Increased roof life
- It supports green building certifications
What Is SRI in Heat Reflective Coating?
The Solar Reflectance Index (SRI) is the most important value that architects should check while selecting heat reflective or cool roof coatings. SRI tells how hot or cool a roof surface becomes when it is exposed to sunlight. The SRI is usually calculated by using two things: Solar Reflectance & Thermal Emittance. Some high-performance cool roof coatings even have SRI values above 100, which means they can stay cooler than normal white paint.
For architects, specifying heat-reflectvie coatings with a high SRI value is more important than just specifying white paint.
Higher SRI = Cooler Surface
Understanding the SRI Scale
| Surface Type | SRI Value |
| Black surface | 0 |
| Grey roof | 30–40 |
| Normal white paint | 60–70 |
| Cool roof coating | 90–120 |
Understanding Solar Reflectance and Thermal Emittance
To understand SRI properly, architects should understand the two important properties: Solar Reflectance & Thermal Emittance.
Solar Reflectance (SR): Solar reflectance is the ability of the surface to reflect sunlight away from the roof. It is measured on a scale from 0 to 1. 0 means the surface absorbs all the heat, and 1 means the surface reflects all the heat. So, the higher solar reflectance means less heat is absorbed by the roof.
Thermal Emittance (TE): Thermal emittance is the ability of the surface to release the heat it has absorbed back into the air. If thermal emittance is high, then the roof releases heat faster and cools down quickly, especially in the evening & night.
What is ASTM & why does it matter in Cool Roof Coatings?
ASTM stands for American Society for Testing and Materials. It is an international organization that creates testing standards for construction materials, coatings, metals, plastics, and other building products. For heat reflective coating, ASTM standards are very important because they make sure that the product is properly tested and the performance values are accurate.
While specifying cool roof coatings, architects should always ask for ASTM test reports, as they help to ensure that the coating will accurately perform as claimed and meet green building requirements.
ASTM Testing ensures that:
- Solar reflectance is properly tested.
- Thermal emittance is properly tested
- SRI is correctly calculated
- Performance claims are genuine
- Architects and consultants can trust the perfect data.
Important ASTM Standards for Heat Reflective Coatings
There are some important ASTM Standards that architects should know while specifying heat reflective coatings. These standards are used to test reflectance, emittance, and also calculate SRI.
| ASTM Standard | Purpose |
| ASTM E903 | Solar Reflectance Test |
| ASTM C1549 | Reflectance Measurement |
| ASTM E408 | Thermal Emittance Test |
| ASTM E1980 | Solar Reflectance Index (SRI) Calculation |
Among all these standards, ASTM E1980 is one of the most important because it is used to calculate the Solar Reflectance Index of the coating. So, when architects ask for product test reports, they should make sure that the product is tested according to these ASTM standards, especially E1980 for SRI.
ASTM E1980 – Why Architects Should Know this Standard
ASTM E1980 is the standard method which is used to calculate the SRI of roof surfaces and coatings. This standard helps to measure how hot or cool a roof surface becomes when exposed to the sunlight. When architects specify heat reflective coatings tested according to ASTM E1980, then they can be sure that the SRI values are properly calculated and reliable. This helps in selecting the right product, meeting green building requirements, and ensuring better thermal performance of the building.
ASTM E1980 is widely used in:
- Cool roof coating specifications
- Green building projects
- LEED Certification IGBC certification
- GRIHA certification
- Energy-efficient building design
Why Architects Should Specify High SRI Coatings
Specifying high SRI heat reflective coatings provides multiple benefits, such as:
Reduces HVAC Load: Cooler roofs mean less heat enters the building, which reduces the load on air conditioning systems
Improves Energy Efficiency: When less heat enters the building, the building uses less electricity for cooling, which saves energy.
Helps in Green Building Certification: High SRI coatings help in getting green building certifications, like LEED, IGBC, GRIHA, and ECBC compliance.
Reduces Urban Heat Island Effect: Cool roof coating helps to reduce the surrounding temperature in cities, which helps in lowering the urban heat island effect.
Increases Roof Life: Lower roof temperature reduces thermal expansion and contraction, which helps to prevent cracks and increases the roof life.
Improves Indoor Comfort: Buildings stay cooler inside, even with lower air conditioning usage.
How Architects Should Specify Heat-Reflective Coatings
Instead of writing just “White reflective paint”, architects should always specify technical performance parameters. This helps to ensure that the right product is selected and the coating performs properly.
Example of Specification Format:
Heat Reflective Roof Coating Specification:
- Minimum SRI: 100
- Solar Reflectance: 0.85 or higher
- Thermal Emittance: 0.90 or higher
- Tested as per ASTM E903, ASTM E408, ASTM E1980.
- Dry Film Thickness: 300 to 500 microns
- Coverage: As per the manufacturer’s specification
- Application Method: Spray or Roller
- Warranty: 5 to 10 years
- Suitable for RCC, metal, and Industrial roofs
- Green building compliant product.
By specifying these technical values instead of just color or brand, architects can ensure proper product selection, better thermal performance, and long-term durability of the roof coating.
Comparison: Normal Paint & Heat Reflective Coating
Normal paint only gives a basic protection, but heat reflective coatings reduce heat gain, improve energy efficiency, help in green building certification, and increase roof life. This comparison table clearly shows why architects should specify heat reflective coatings instead of normal paint.
| Property | Normal Paint | Heat Reflective Coating |
| SRI | 10–30 | 90–120 |
| Roof Temperature | Very High | Much Lower |
| Heat Gain | High | Low |
| HVAC Load | High | Reduced |
| Energy Savings | No | Yes |
| Green Building | No | Yes |
| Roof Life | Normal | Longer |
Conclusion
Now, heat reflective coatings are very important for modern and climate-friendly building design. Architects should not choose coatings based only on color, but also on performance values like SRI and ASTM test standards. In the above blog, we have provided a complete guide on Specifying Heat Reflective Coatings: What Architects Need To Know About SRI & ASTM. Hope this will help architects to correctly specify heat reflective paints for better building performance.
For those architects who are looking to provide the best results, COOLROOF® paints offers high-quality, ASTM-tested Heat reflective coatings that can turn the technical requirements into reality. By choosing COOLROOF® paints, you aren’t just applying a coating, you are making a cooler and more sustainable future for every structure you design.
