How do metal roof screws with rubber washers work?
Short answer. Metal roofing screws with rubber washers seal each hole by compressing an EPDM or similar rubber washer, bonded to a small steel washer under the screw head, against the panel as the screw is driven. Driven straight and just snug, the washer forms a tight seal; overdriven, it squashes out and cracks, and underdriven, it never seals.
Parts of the screw
- Head: usually a hex washer head, often painted to match the panels.
- Sealing washer: a steel washer with bonded EPDM rubber.
- Threads: coarse wood threads for wood decking or purlins, or self-drilling points and finer threads for steel framing.
- Coating: corrosion-resistant coatings rated for exterior exposure, with stainless steel for special cases.
Common sizes
Typical residential screws are #9 or #10 diameter in lengths from about 1 to 2 inches, long enough to bite solid wood. Oversize repair screws, often #12 or #14, go into stripped holes. Follow the panel maker's fastener schedule.
Driving them right
- Drive perpendicular to the panel.
- Stop when the rubber just begins to show at the edge of the steel washer: snug, not crushed.
- Use a screw gun with a clutch or depth setting rather than an impact driver at full power.
- Hit the framing or purlin; screws into thin decking alone can pull out.
- Place them where the panel maker specifies, in the flat or on the rib.
When to replace
Cracked, hardened or missing washers, rust trails and backed-out screws mean it is time. In Georgia sun, many exposed-fastener roofs need a fastener check and partial replacement at some point in their life. Replace with the same type, or one size up in stripped holes.
See metal roofing in Georgia and common causes of roof leaks.