New Products: A Standing Seam Screw for Wood Decks and a High-Temp Underlayment

Two products in Roofing Contractor’s October product focus on metal and metal accessories are aimed squarely at the residential standing seam job: a Teks standing seam screw built for wood decking and framing, and a RhinoRoof High-Temp self-adhered underlayment. Here is what was announced, why wood-deck fasteners and high-temperature underlayment are their own problems, and how to judge any fastener or underlayment for a metal roof regardless of the name on the box.

What was announced

Teks launched a standing seam roofing screw designed for wood decking and framing in both flanged, or nail strip, and clip-based standing seam systems. RhinoRoof introduced a High-Temp self-adhered underlayment. Both appeared in the October product focus; our news snips on the Teks screw and the RhinoRoof underlayment have the source. We have not tested either product and this post is not a review. It is a look at the problems they are built for.

Why wood-deck fasteners are their own problem

Commercial standing seam grew up on steel purlins and metal deck, and a lot of the fastener catalog still reflects that: self-drilling points, thread forms for steel, heads sized for clips on structural members. Residential standing seam goes down on plywood or OSB over rafters or trusses, often 7/16 to 5/8 inch sheathing, and the fastener has a different job. It has to grab thin wood, resist pull-out when the roof is working in wind, sit low enough under the panel that it does not telegraph through, and not split or spin out the sheathing when the installer drives it.

Nail strip panels add another wrinkle. The fastener goes through the panel flange itself, so head shape and the way the slot in the flange allows movement both matter. A head that is too tall or a screw driven too tight pins the panel and fights thermal movement; too loose and the panel rattles and the hole wears. A screw designed for the flange is a real improvement over whatever pancake head was in the truck.

What to look for in any standing seam fastener

• Head: a low-profile pancake or wafer head for clips and flanges, so nothing shows through the panel above it.
• Thread and point: a wood-thread form with a sharp point for decking, not a self-drilling steel point. Threads that run most of the length hold better in thin sheathing.
• Length: long enough to fully penetrate the sheathing, and to reach framing where the manufacturer’s clip schedule calls for it.
• Corrosion resistance: a coating rated for the exposure, and compatibility with the panel metal. Aluminum and copper roofs call for stainless or otherwise compatible fasteners to avoid galvanic corrosion.
• Drive: a drive that lets a crew run hundreds of screws a day without cam-out, and that matches the bits you carry.
• The tested assembly: wind uplift assemblies tested to ASTM E1592 or UL 580 are tested with specific clips and fasteners. Substituting a fastener can take you outside the tested assembly, and outside the warranty. Check the panel manufacturer’s approved fastener list.
• Pull-out and pull-over data for the substrate you use, from the fastener maker, if the job is engineered.

Why metal needs a high-temperature underlayment

A metal panel in summer sun gets hotter than an asphalt shingle, and a dark panel gets hotter still. A conventional self-adhered ice and water membrane, built for use under shingles, can soften, flow and bleed adhesive at those temperatures, and that adhesive then bonds to the back of the panel or runs out at the eave. High-temperature self-adhered underlayments are formulated to stay stable at higher service temperatures. The rated temperature is on the data sheet, and many metal panel manufacturers call for a high-temp product under their panels, especially under dark colors and on low slopes.

The self-adhered sheet also does the second job every metal roof needs: a watertight secondary layer that seals around every clip screw and fastener penetration, and a water barrier at eaves, valleys, penetrations and low slopes where wind-driven rain and ice damming push water uphill under the panel. Synthetic mechanically attached underlayments remain common in the field of steeper roofs, with self-adhered high-temp in the vulnerable areas, or self-adhered over the whole deck where the manufacturer or the slope calls for it.

Copper and zinc add one more requirement. Some underlayments and some substrates can stain or corrode those metals from below, so manufacturers commonly specify a slip sheet or a specific compatible underlayment beneath them. Our homeowner guide on underlayment and ventilation covers the basics from the customer’s side.

What to look for in any underlayment under metal

Putting both together on a wood-deck job

1. 1
   Read the panel manufacturer’s installation guide and pull the approved fastener and underlayment lists before you order anything.
2. 2
   Specify a high-temp self-adhered underlayment at eaves, valleys, penetrations and low-slope areas at minimum, and over the whole deck where the manufacturer, the slope or the climate calls for it.
3. 3
   Select a fastener built for the substrate wood-thread form, low-profile head, correct length and coating, matched to the clip or flange and to the panel metal.
4. 4
   Set the clip and fastener schedule from the manufacturer’s chart for your wind zone, not from habit.
5. 5
   Drive a few test fasteners into a scrap of the actual sheathing and check seating, stripping and head height before the crew starts.

New fasteners and underlayments arrive every season. The ones worth your attention are the ones built for the roof you actually install, and the way to judge them is the same every time: read the data sheet, check it against the panel maker’s requirements, and test it on a scrap before the crew does. Suppliers of fasteners and underlayment for metal roofing are welcome to list in our supplier directory.