Ideal Dry Film Thickness (DFT) for Cool Roof Paint on Metal and PEB Roofs- In today’s industrial environment, rising temperatures and increasing energy costs have made cool roof paint an essential requirement for factories, warehouses, and PEB (Pre-Engineered Building) structures. These roofs are typically made up of metal sheets that absorb a high amount of solar heat, which leads to uncomfortable indoor conditions, and this has also increased dependency on cooling systems. However, the performance of cool roof paint does not only depend on the product quality, but also on applying the correct Dry Film Thickness (DFT).
Dry Film Thickness (DFT) plays a key role in determining the paint’s heat reflectivity, durability, waterproofing, and overall lifecycle performance. For large-scale roofing, incorrect DFT can lead to premature coating failure, rejection during inspection, and loss of warranty.
In this blog, we will discuss what DFT is, why it matters, and the Ideal Dry Film Thickness (DFT) for Cool Roof Paint on Metal and PEB Roofs to ensure long-lasting protection and maximum heat reflection. This blog will help contractors, factory owners, and project managers to make informed decisions.
What is Dry Film Thickness (DFT)?
Dry Film Thickness (DFT) is known as the thickness of the paint coating after it has been fully applied, dried, and cured. When cool roof paint is applied in liquid form, it contains solvents or water that gradually evaporate during the drying process. After evaporation, only the solid coating remains on the surface, and this final layer is measured as DFT.
Dry Film Thickness (DFT) is usually measured in microns (µm) and represents the actual protective layer left on the surface. DFT is different from Wet Film Thickness (WFT), which is measured immediately after application. DFT determines the durability, solar reflectivity, weather resistance, and long-term protection of the roof.
Why is DFT important for Metal and PEB roofs?
Metal and PEB roofs are usually exposed to extreme environmental conditions, such as intense sunlight, thermal expansions, rain, humidity, and industrial pollution. An incorrect DFT can reduce the overall effectiveness of the cool roof system, and maintaining the correct DFT ensures that the cool roof system performs effectively throughout its service life. An Ideal Dry Film Thickness is very important because:
- DFT ensures maximum solar reflectivity.
- It improves the thermal insulation and indoor comfort.
- Dry Film Thickness also protects metal surfaces from UV rays, moisture, and corrosion.
- This increases the coating lifespan.
- In addition, DFT prevents premature peeling, cracking, or fading.
- Ideal Dry Film Thickness (DFT) for cool roof paint on Metal and PEB roofs, helps to maintain manufacturer warranty & performance.
Also Read: Benefits of High SRI Cool Roof Paint
Recommended Ideal DFT for Cool Roof Paint on Metal and PEB Roofs
For large factories and long-term projects, choosing a higher DFT within the recommended range is better, as it helps the coating to last longer and to reduce the need for frequent maintenance. While the exact Dry Film Thickness (DFT) may depend on the type of product which is used on the site conditions.
The following DFT ranges are commonly followed in industrial cool roof applications:
| Roof Type | Recommended Total DFT |
| Metal Roofs (GI / Aluminium Sheets) | 150–200 microns |
| PEB Roof Structures | 200–300 microns |
| High-Heat, Coastal, or Heavy Industrial Areas | 250–300 microns |
How DFT Is Measured on Metal & PEB Roofs?
In professional and bulk projects, DFT is checked by using magnetic or electronic DFT gauges that are especially made for painted metal surfaces. To get accurate results of measurement, best practices include taking several readings from different areas of the roof and then calculating the average thickness. These readings of the coating should be recorded properly and checked as per the BOQ or contract requirements.
In many projects, Dry Film Thickness for Cool roof coating is checked in front of the client for transparency. Also, for the factory and the warehouse projects, measuring DFT is often compulsory before the final handover of the work.
Common DFT Mistakes to Avoid in Industrial Cool Roof Applications
When good quality materials are used in roof coating, wrong application methods can reduce the life of the PEB roof coating. Some common Dry film thickness mistakes have been seen in many industrial projects, which should be avoided to get better results. These mistakes can weaken the coating, lead to early failure, cause rework, increase overall project costs, and result in poor client satisfaction.
DFT Mistakes that should be avoided in industrial cool roof coating applications are:
- Applying a thinner coating than required to save paint material.
- Applying too much paint in a single coat can cause cracking or peeling after drying.
- Uneven spray or roller application, which leads to different DFT levels across the roof.
- Ignoring proper surface preparation that affects paint bonding and DFT stability.
Also Read: How Cool Roof Coatings Extend Roof Life
Effects of Incorrect DFT Application
Applying the coating within the recommended range ensured balanced performance and durability.
Problems Caused by Low DFT
- Reducing the cool roof effectiveness and poor heat reflection.
- Causes faster damage from sunlight and UV rays.
- Shorter coating life and frequent maintenance needs
- Higher risk of rust and corrosion on metal surfaces.
Problems Caused by Excessive DFT
- Cracking or peeling of paint after drying.
- Improper or uneven curing of the coating
- Weak bonding between the paint and the roof surface.
- Wastage of material and higher project cost.
Importance of Surface Preparation in Maintaining Ideal DFT for Cool Roof Paint on Metal and PEB Roof
In Industrial and government projects, DFT is usually mentioned as a compulsory technical requirement, and surface preparation plays a direct role in achieving correct DFT and good coating performance. Even if the right amount of paint is used, a poorly prepared surface can cause uneven thickness and early coating failure. Surface preparation before roof paint coating is essential, because a clean and properly prepared surface allows the cool roof paint to spread evenly and helps to achieve the required Dry film thickness for long-lasting protection.
For maintaining an ideal DFT for cool roof coating on Metal and PEB roofs, proper surface preparation includes:
- Removing rust, grease, oil, and loose or peeling paint.
- Cleaning dust and other surface contaminants.
- Repairing damaged or rusted metal areas.
- Applying a suitable metal primer before coating at the needed site.
How to Clearly Mention DFT in Cool Roof Tenders and Contracts
For bulk contracts, DFT should be clearly mentioned in the scope of the work and the BOQ (Bill of Quantities). Clear DFT specifications help to prevent confusion during application, inspection, and final project approval. A clear and well-written specification of DFT in cool roof contracts should include:
- Total required DFT in microns.
- Number of coats and minimum thickness for each coat.
- Surface preparation requirements.
- Method of DF measurement and acceptable tolerance limits.
- Inspection and record-keeping requirements.
Conclusion
Achieving the ideal dry film thickness (DFT) for cool roof paint on metal and PEB Roofs is essential for maximising the performance of cool roof coating. For factories, warehouses, and large industrial structures, correct DFT ensures long-term durability, better heat reflection, energy savings, and reduced maintenance. In this blog, we have mentioned complete information about DFT for metal and PEB roofs.
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FAQs (Frequently Asked Questions)
What is the ideal Dry Film Thickness (DFT) for cool roof paint?
The ideal DFT depends on the roof type and exposure conditions. Generally, metal roofs require 150–200 microns, PEB roofs need 200–300 microns, and high-heat or coastal areas perform better with 250–300 microns.
What happens if DFT is lower than recommended?
Low DFT can lead to poor heat reflection, faster UV damage, early coating failure, and higher chances of rust or corrosion on metal roofs.
Is DFT measurement mandatory in industrial projects?
In most industrial, warehouse, and government projects, DFT measurement is compulsory and is checked before final handover as per BOQ or contract specifications.
How many coats are usually needed to achieve proper DFT?
Most cool roof systems require 2 or more coats, with specific thickness per coat, depending on the product and final DFT requirement.
Who benefits most from maintaining correct DFT?
Contractors, factory owners, consultants, and project managers all benefit through better performance, smooth approvals, warranty protection, and reduced maintenance costs.
