As design professionals, understanding the optimal substrate for your projects can significantly impact efficiency, durability, speed of build and overall cost-effectiveness. In this detailed comparison, we delve into the technical advantages of metal tray over traditional plywood substrates, offering insights into their application in today's construction environment.

Traditional plywood substrates

Historically, plywood has been a staple in NZ construction, particularly in residential settings where its structural integrity and versatility are valued. On a typical plywood flat roof substrate, rafters and nogs must be installed at 400mm centres, plywood substrates require meticulous assembly, including staggered sheet layouts and hundreds, sometimes thousands of stainless-steel screws installed at 150mm centres around the perimeter and 200mm through the centre of the sheet (approximately 80 per sheet) and then also glued down. This labour-intensive process is further complicated by the need for effective moisture management, potentially delaying membrane application until optimal drying conditions are met.

It is no secret the cost of timber has risen substantially over recent years, affecting overall project budgets. This substrate's susceptibility to absorbing moisture and reduced insulation efficiency over time are additional considerations, making it less favourable in terms of long-term performance and maintenance.

Metal tray substrates

Compared with plywood, metal tray substrates provide far more rapid installation and improved structural efficiency. Consisting of prefabricated metal trays placed over minimal purlins, this system supports fast, weathertight construction progress, allowing simultaneous work underneath and above the roof structure. Significantly less roof framing is needed for a metal tray, the support beams can span up to 3600mm (internal span), while still maintaining a strong structure. Metal trays can be supplied at any length, reducing the number of joins.

The advantages of metal tray substrates extend beyond application speed. They do not absorb moisture, ensuring consistent performance and eliminating delays associated with weather events. These advantages also support immediate membrane application, enhancing project timelines and reducing overall construction costs.

For example, Micah Hoskins, a certified Nuralite waterproofing applicator from Complete Waterproofing Works, installed a 300 square meter metal tray roof substrate in a single day with three workers. Whereas a plywood and timber substate would have taken ten times longer with no allowance for inclement weather during the build.

In summary

Traditional Plywood Substrate:

Set-up: A traditional plywood set-up features plywood sheets which are placed over a grid of wooden rafters and nogs. This structure requires meticulous assembly, including staggered sheet layouts, glued and numerous stainless steel screws installed at 150mm centres around the perimeter and 200mm through the centre of the sheet (approximately 80 per sheet)

Pros:

• Structural integrity and versatility, especially valued in residential settings.
• Reliable historical performance in various construction applications. 

Cons:

• Labor-intensive and prolonged installation process.
• Susceptibility to moisture, which can delay further construction.
• Rising timber costs affecting overall project budgets.

Metal Tray Substrate:

Set-up: A metal tray substrate system features prefabricated metal trays which are placed over minimal purlins. This setup supports rapid construction progress, with significantly less roof framing needed.

Pros:

• Rapid installation and improved structural efficiency.
• Prefabricated trays can be supplied at any length, reducing the number of joins.
• Excellent moisture management, ensuring consistent performance and immediate membrane application.
• Reduced maintenance requirements and lower long-term costs.

Cons: 

• Slightly higher roof build up due to thickness in metal profile.

Conclusion

While traditional plywood substrates offer structural reliability and versatility, metal tray systems present significant advantages in terms of construction efficiency, durability, and cost-effectiveness. The swift installation of metal trays, coupled with their superior moisture management and reduced maintenance requirements, makes them a compelling choice for modern roofing projects. Nuralite supports this shift towards metal tray substrates based on their proven performance and alignment with industry trends towards efficiency and sustainability.

Nuralite products are versatile and can be applied to various substrates such as plywood, concrete, metal trays, and CLT timber substrate as well on top of tapered PIR boards. Additionally, one of Nuralite’s favorite is to extend the lifespan of an existing metal tray roof by applying a new membrane.

All of these options are within the scope and limitation of the Nuraply CodeMark Certificate for further confidence and for ease of consent.

Contact the Nuralite team to discuss your project