Exposed-fastened (EF) metal roofing is a popular choice for industrial and agricultural applications thanks to its durability and resistance to sun, wind, snow, hail, algae growth, pests and fire. Compared to standing seam metal roofs, the appeal of EF roofs lies in its lower cost and ease of installation. One of the greatest challenges with EF roofing, however, is proper waterproofing.
This roof type consists of overlapping corrugated or trapezoidal rib panels secured either through the roof deck or fastened together over open framing. Securely attaching snow retention systems, solar photovoltaic (PV) panels or utilities to your EF roof requires penetrations into the rib panel and/or structure. Every penetration (or hole) is at risk for moisture intrusion. If not properly sealed, holes can cause corrosion and lead to water leakage onto surfaces below the roof and into the building interior.
To protect the durability of your metal roof and the service life of the installed system, it’s critical to use high-quality brackets and fasteners fabricated with top-notch gaskets and sealants.
Sealant Application
Sealant chemistry varies, and even good sealants may be compromised by poor application and exposure to environmental conditions.
Avoid surface-applied sealants and caulking.
Externally applied sealants may seem to protect the penetration area, but this method leaves proper execution to chance. Surface-applied sealants also deteriorate, dry out and crack over time from exposure to ultraviolet (UV) rays, harsh weather, dirt and contamination.
Use non-corrosive metal brackets and fasteners with factory-applied sealants.
Factory-applied sealants take the guesswork out of purchasing and applying an external sealant, which may result in the use of an inferior product or installation. Factory application places the sealant in the exact location needed, which eliminates mess and provides a more effective seal. High-quality brackets conceal the sealant from the elements to help the protective seal remain stable over time.
Butyl and EPDM Offer Exceptional Weatherproofing
Two sealants in the marketplace provide proven weathertight performance: butyl copolymer tape sealant and EPDM. Each sealant’s properties lend themselves to specific metal roof attachment locations, which varies with the type of system or accessory you mount and the weather conditions at the building’s location.
Butyl Tape Sealant Offers Top Performance for Mounting Snow Retention in the Valley of the Corrugation or Ribbed Panel’s Flat
When attaching a snow retention system to your EF roof (or if your building is located in a high wind zone), it’s imperative to attach into the support structure for adequate holding strength. Fasteners will need to penetrate through the flat area between trapezoidal ribs of the panel (or the low valleys of a corrugated roof) and into the wood decking, wood or steel purlins, or trusses. Because these areas of the panel are drainage planes where water and moisture flow, your choice of sealant is critically important.
Butyl tape sealant has been time-tested through decades of service.
Butyl polymer tape sealant has an estimated performance life of more than 60 years. A copolymer of isobutylene with isoprene, butyl sealant remains sticky and flexible even in extreme temperatures. Butyl sealant conforms to irregular surfaces like the panel’s minor ribs and striations to create a watertight seal.
Certain strategies enhance butyl’s longevity.
Despite butyl polymer’s outstanding impermeability, certain techniques improve its performance. Look for brackets with pre-applied butyl sealant enclosed in a reservoir at the base of the bracket and pre-punched holes for fasteners. This fabrication technique encases the attachment site within the sealant to block water intrusion. The reservoir also shields the butyl from UV rays to prevent degradation and provides a buffer to prevent over-torquing the fasteners. Additionally, as the fastener is driven into the substrate, it pulls the butyl into the fastener’s threads for another layer of protection. A fastener with an EPDM washer (gasket) prevents moisture intrusion from the top. When combined with a butyl reservoir bracket, the attachment becomes triple sealed.
EPDM Prevents Moisture Infiltration When Mounting PV Panels in the Top of the Corrugation or Rib Panel
In applications where heavy snow is not a consideration, PV modules or light-duty applications can be attached at the top of your roof’s rib panel or the crest of the corrugation.
EPDM has an impressive track record of moisture resistance.
Commonly used as a commercial roofing material, EPDM has a 50-year service history of watertight performance when shielded from UV rays. EPDM is a semi-hard, synthetic rubber composed of ethylene propylene diene monomer. Because the surface of EPDM is not gummy, it needs to attach to a smooth plane like the sides of a roof panel’s rib to form a proper seal. Once secured in place, EPDM offers high-tensile strength and will endure extreme temperatures well.
Double seal with EPDM
The most weathertight attachments provide more than one seal at penetration points. Find vendors who offer factory-applied EPDM on the feet of the bracket and EPDM gaskets on the fasteners to obtain a double seal.
Verify the Attachments’ Weathertight Qualities
Without testing it’s impossible to substantiate a product’s weathertight claims. ASTM International provides technical testing protocols to evaluate products for quality and performance. To examine water intrusion through metal roof panel systems, ASTM offers two relevant tests: ASTM E2140 and ASTM E1646.
ASTM E1646 sprays water directly at the joint or point of penetration to simulate wind-driven rain. Minor vacuum pressure is applied from below in an effort to pull the water through the sample and assess its water resistance.
The ASTM E2140 test is a much more demanding test and strongly preferred. It evaluates water leakage at roof plane penetrations by submerging the joint or assembly beneath 6 inches (15.24 centimetres) of static water pressure for six hours. The system fails if even one drop of water penetrates the joint.
Ask the product vendor for proof of its testing (a test report of the ASTM 2140 procedure) from an independent lab.
How to Protect Your Roof from Water Intrusion and Leakage
Mounting snow retention, solar PV panels, utilities or accessories to your EF metal roof requires penetrations to be correctly sealed. When fabricated into a properly designed bracket system, butyl and EPDM sealants create a reliable barrier against corrosion, rust and water infiltration. With butyl and EPDM sealants, you gain the best protection on the market to preserve your roof’s longevity. For information and videos on this topic and more, please visit www.s-5.com or www.metalconstruction.org.
