Purlin Tail Self-Tapping Screws for Flexible Roofing (FM 4470)
Flexible membrane roofs — TPO, EPDM and PVC — need a fastener that anchors the membrane and insulation to the steel purlin without piercing damage. The purlin tail self-tapping screw is engineered for exactly this: a case-hardened CR-10 shank with a self-tapping point that grips the purlin web, finished with a stress-spreading plate or bonded washer that holds the system against wind uplift. Supplied to membrane roofing contractors to FM 4470 requirements.
Features and Benefits
- Self-tapping purlin tail grips the purlin web with high pull-out values in thin structural steel
- Case-hardened CR-10 coating — engineered for long-term corrosion performance under the membrane
- Wide stress plates up to 29 mm spread the clamp load over insulation and membrane without tearing
- Assemblies tested to FM 4470 wind-uplift protocols for approved roofing systems
- Consistent heat treatment for torsional strength during power installation
Typical Applications
- TPO, EPDM and PVC single-ply membrane roofing systems
- Fastening insulation boards to steel purlins and decks
- Fabric and membrane structures
- Retrofit re-fastening of loose-laid roofing
- Steel-frame buildings with exposed fastener details
Model Specifications
| Thread Size | Length Range | Point Style | Plate / Washer | Coating |
|---|---|---|---|---|
| #12 (5.5 mm) | 50-100 mm | Self-tapping, 25° needle | 25 mm steel plate | CR-10 |
| #14 (6.3 mm) | 65-150 mm | Self-tapping, 25° needle | 25-29 mm steel / aluminum plate | CR-10 |
| #15 (7.0 mm) | 100-150 mm | Self-tapping, 25° needle | 29 mm aluminum plate | CR-10 |
Material and Performance
- Material: 10B21 carbon steel, case-hardened, core HRC 32-40
- Coating: CR-10 multi-layer corrosion protection, AS 3566 Class 4 class performance, 1,500 h salt spray
- Pull-out: verified against purlin thicknesses from 1.5 mm to 3.0 mm — request the test table for your gauge
- Certification: FM 4470 assembly approval available for specified systems; ISO 9001 factory
Installation Guidelines
- Fasten through the membrane and insulation into the purlin web at the spacing specified by the system designer.
- Use an adjustable torque screw gun so the plate seats flat without rotating and tearing the membrane.
- The plate must sit square to the surface — a tilted plate cuts the membrane edge under wind load.
- Do not overdrive: the plate should compress the insulation evenly, not punch through it.
- Keep fasteners within the corrosion class specified for the building interior — CR-10 covers most exposed applications.
Why Source from BuildFastener
We supply screws, plates and washers as a matched assembly and release test reports for pull-out and coating on request. Engineers are available to review your purlin gauge and insulation build-up before you order. Send your specification for project pricing.
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