Standing seam roofs are superior to screw-down roof systems for several reasons.
The most obvious is weather tightness. Standing seam roofs utilize a clip to attach the panel to the roof framing, minimizing the use of exposed fasteners. Fewer fasteners (or penetrations in general) mean less likelihood of leaks.
Handling panel expansion and contraction is another area in which standing seam roofs provide superior performance. Metal roof panels will expand and contract based on the roof panel temperature. Standing seam roofs with sliding-style clips allow the panel to expand and contract without damaging the roof panel.
Screw-down roofs have to allow for this expansion and contraction as well. They assume the roof purlins will roll or move a bit to allow for some expansion. But over time, you will find that the panel around the fastener locations will start to enlarge due to the panel movement.
Screw-down roofs also require more ongoing maintenance. All metal roof systems require maintenance. One of the most important preventative maintenance tasks is checking all fasteners. You check to make sure they are still tightened as they were intended to be when initially installed. You check to ensure the rubber gasket is still intact, as they all deteriorate with time, especially when initially over-tightened. You check to ensure the panel isn’t widening around the fastener, as mentioned above. And whatever fastener is not up to snuff, you replace. It’s easy to see a standing seam roof that minimizes the number of fasteners will take less effort to maintain than a screw-down roof.
While we have always educated our clients about the superior performance of standing seam roofs, there have always been several owners who were only concerned about price, and the screw-down roof cost less, so we installed it. (You may wonder how installing all those fasteners is quicker than using a standing seam clip system. This point can be argued either way, but one of the real savings of a screw-down roof is the ability to utilize a 26ga panel versus a minimum of 24ga for standing seam roofs.)
But the stricter performance requirements of modern energy codes have dealt a real blow to screw-down roofs.
The energy code essentially requires the use of a thermal spacer block. A thermal spacer block is a piece of rigid insulation, typically either EPS or XPS, that is installed over the purlin. Fiberglass insulation, when compressed, provides little to no resistance to the transfer of heat. Utilizing a thermal spacer block made from rigid insulation mitigates heat transfer through the panel-purlin connection and increases the thermal performance of the overall roof.
If you utilize the R-value method to comply with the energy code, you are required to use a thermal spacer block.
If you use the U-factor method, you can use a screw-down roof. But you won’t find a screw-down roof system utilizing fiberglass insulation that can meet the U-factor requirements of the most recent International Energy Conservation Code of 2018. (With the exception of Climate Zone 1, which includes Hawaii, Puerto Rico, the Virgin Islands, and Broward, Dade, and Monroe counties in Florida. In Climate Zone 1, you can use a liner-style system utilizing R-19 & R-11 insulation and a screw-down roof which has a U-factor of 0.044; the minimum requirement for non-residential buildings.)
So, is the screw-down roof officially dead?
There is still a place for screw-down roofs. Unconditioned buildings, which are exempt from complying with the energy code, may still find them useful. We construct some buildings that don’t even have walls for pure covered storage. It doesn’t make sense to me to put a standing seam roof on a building without walls. The standing seam roof provides superior weather tightness, but if you have open walls with a strong wind, the area under cover can just as easily get wet.
Also, if you’re in the pole barn business, screw-down roofs will continue to remain the standard. Screw-down roofs are used in pole barns to create diaphragm bracing to handle lateral loads such as wind and seismic that act on buildings. There are other methods to handle these loads, but utilizing the metal roof & wall sheeting as a diaphragm is the most cost-effective.
But screw-down roof systems are largely a thing of the past for pre-engineered metal buildings.