Choosing the correct Jumbolon insulation thickness is the most critical factor in maximizing your building’s energy efficiency and achieving long-term comfort. Jumbolon, which is a brand of Extruded Polystyrene (XPS) foam, is a premium choice for roof assemblies due to its superior moisture resistance and high compressive strength.
However, thermal performance is directly proportional to thickness. Too thin, and you waste energy; too thick, and you overspend on materials. This guide will help you determine the best thickness for your roof insulation project based on performance requirements and climate.
The Core Metric: R-Value and Thickness

The insulating power of any material is measured by its R-value, which denotes thermal resistance to heat flow. The higher the R-value, the better the insulation performance.
1. Jumbolon’s Thermal Advantage
Jumbolon (XPS) typically provides an R-value per inch ranging from R-5.0 to R-5.3. This high R-value means it can achieve significant thermal protection with less material compared to traditional insulation types.
2. Required R-Value by Climate
The ideal total R-value for your roof assembly is dictated by your geographical climate zone. In regions with very hot summers or cold winters, higher resistance is necessary to maintain a comfortable interior temperature and reduce utility costs.
- Hot Climates (Cooling Dominated): To prevent heat ingress, a minimum roof R-value of R-20 to R-30 is often required, depending on local building codes and the intensity of solar heat.
- Moderate/Mixed Climates: R-values in the range of R-30 to R-40 provide a good balance for both heating and cooling seasons.
- Cold Climates (Heating Dominated): These zones demand the highest levels of protection, typically requiring R-49 to R-60 or more to minimize heat loss.
Determining the Best Thickness for Roof Insulation

Moreover, based on Jumbolon’s average R-value of R-5.0 per inch, here is a breakdown of the thickness required to achieve common target R-values:
| Target R-Value | Jumbolon Thickness (Inches) | Primary Application |
| R-10 | 2 inches (2 * 5.0) | Minimal requirement; often used in light-commercial or shed roofs. |
| R-20 | 4 inches (4 * 5.0) | Recommended minimum for residential roof insulation in moderate climates or for commercial buildings needing adequate heat proofing. |
| R-25 | 5 inches (5 * 5.0) | Ideal mid-range thickness, providing high energy efficiency in hot climates where solar load is severe. |
| R-30 | 6 inches (6 * 5.0) | Excellent for high-performance residential homes or in areas with stringent thermal protection standards. |
Furthermore, for most residential and commercial flat roof insulation projects in hot to moderate climates. However, a thickness between 4 to 5 inches (100mm to 125mm) is considered the best thickness for balancing material cost and long-term thermal performance.
Factors Influencing Your Final Decision
While R-value is paramount, other factors specific to Jumbolon and its application should guide your final purchase:
1. Application Type: Inverted vs. Conventional Roof
- Inverted Roof (Most Common with XPS): In this system, the Jumbolon (XPS) boards are laid above the waterproofing membrane. This is ideal because the insulation shields the membrane from temperature extremes and UV damage, greatly extending its lifespan. Since the XPS is exposed to water from rain and snow, its excellent moisture resistance is critical.
- Conventional Roof: The insulation is placed below the waterproofing membrane.
2. Load-Bearing Requirements
Jumbolon is known for its high compressive strength, making it suitable for rooftops that see pedestrian traffic, heavy equipment, or support green roof assemblies. If your roof will be a walkable terrace or support air conditioning units, ensure you select a high-density Jumbolon board, regardless of the thickness required for thermal efficiency.
3. Moisture Resistance and Long-Term Value
The closed-cell structure of Jumbolon ensures negligible water absorption, meaning its R-value is maintained even if the roof assembly gets wet. Investing in sufficient thickness ensures long-lasting insulation. That will continue to deliver performance for decades, offering better lifetime value and maximizing your potential energy savings.
Conclusion: Optimal Thickness
For a comprehensive and effective roofing system, the sweet spot for Jumbolon insulation thickness is generally 4 inches (100mm) for adequate thermal protection in most average climates, or 5 to 6 inches (125mm to 150mm) if you are aiming for superior energy efficiency in an extreme climate zone or seeking to meet high-end green building standards. Always verify the required total R-value with your local building code before making a final decision.
FAQ’S
The total R-value (or thermal resistance) of your Jumbolon insulation is calculated linearly based on its thickness. Since Jumbolon (Extruded Polystyrene – XPS) typically offers an R-value per inch of around R-5.0, a 4-inch board provides an R-20, and a 6-inch board provides an R-30. To achieve high energy efficiency and the required thermal protection. However, you must select the best thickness that meets or exceeds the local code’s minimum R-value requirement for your specific climate zone.
In both very cold and very hot climate zones, a higher total R-value is required to ensure thermal protection and maximize efficiency. Cold climates, a thicker layer provides better resistance against heat escaping (heat loss). In hot climates, the insulation must resist the intense solar load (heat gain). However, choosing a sufficient Jumbolon insulation thickness (often 5 to 6 inches) minimizes the work required by your HVAC system, translating directly to lower utility bills.
While moisture resistance doesn’t directly dictate the thermal thickness, it is a key factor in ensuring long-lasting insulation. The closed-cell structure of Jumbolon prevents water absorption, which means the installed R-value is maintained over decades, even in challenging environments like a flat roof insulation system. Furthermore, this long-term stability ensures the thickness you select for your target R-value. Which continues to perform reliably throughout the building’s life.
For a standard residential roof insulation project in a moderate to mixed climate. While the best thickness of Jumbolon is typically 4 inches (providing R-20) to 5 inches (providing R-25). This range offers an excellent balance between the material cost and achieving very good thermal performance. However, you should always consult local building codes as many jurisdictions now require R-30 or higher for superior heat proofing and long-term energy savings.



























