Since 2003, ANSI SPRI ES1 has been in place to assist designers, manufacturers, owners, and contractors in the prevention of failure of perimeter edge metal assemblies in low slope roofing systems. Edge metal often serves as the primary method of membrane securement, is a visible success or failure measure, and is required to absorb the primary impact for the roof in a high wind event. What do we do to ensure that these tested and code compliant assemblies are transferring load to other stable and sustainable components which will at minimum, absorb the load transfer?
Nailers made of wood continue to be the dominate choice in commercial building perimeter joinery. This is primarily due to initial cost, availability, and standard practice. There are numerous considerations as we begin to evaluate how best to protect the perimeter of a facility. Is the design suspect to moisture, mold and rot from condensation and water intrusion? Will the component selected warp over time creating uneven and weak connection points? Will the type of fastener utilized react with the substrate, causing rust or decay? Is the labor needed to create the nailer viable economically with radius, convex/concave, or a high build nailer condition. With current insulation requirements in code, it is not uncommon to find tapered insulation in roof assemblies with nailer builds which exceed 12” in height at the perimeter. Many of these questions fall back on the designer to address, and it can be helpful for designers to have resources for reference on wind uplift and attachment as well as proper designs for tying in thermal, air, and vapor barriers in their design.
In image 1, we find a coping which remained attached to a shimmed nailer made of wood components. The assembly released not only from the substrate under wind duress, it also experienced a torsion load deformation, twisting the wood components as it sheared off the building perimeter.
In image 2 we find a multi-component nailer with suspect design and many potential current and future flaws. This perimeter provided a limited solid surface to secure a membrane, left a variable and unpredictable load endurance capacity, and presented a deficiency in the installer’s ability to prevent air and water intrusion. Aesthetically, there was also considerable potential for the wavy substrate appearance to mirror through any finished assembly.
In image 3, we find plywood utilized to generate a radius condition that provided a highly variable continuity of load, significant height variation for the installer to deal with, and represented the potential for more rapid deterioration from condensation in air pockets and gaps.
|FM1-49||FM Global Property Loss Prevention 2016||18.104.22.168||5-8|
|ANSI SPRI ED1||Design Standard for Edge Systems Used with Low Slope Roofing Systems||3.8, 4.3||19, 20, 24, 25, 27|
|IBC Chapter 23||Wood||2301||1-8|
The good news is there are various resources which address nailers and their importance in commercial buildings. These standards are meant to provide a baseline guide for specifiers and installers to reduce a hidden weakness from occurring at the perimeter of your roof assembly.
The most recent of these documents, the ANSI SPRI ED1 Design Standard for Edge Systems Used with Low Slope Roofing Systems, which became ANSI approved June 3rd, 2019, a designer is presented with tables A6 and A7 which provide Nailer Attachment Fastener Loads for buildings above and below 60’ in height. Based on the Field of Roof Pressure psf (kPa) in a simple to use format, the designer is provided corresponding data for fastener spacing and the perimeter fastener load. This becomes critical for designers attempting to address unique conditions and heights of nailers, and can be a useful guide for the maintenance of continuity in the perimeter.
In addition, ED1 provides the designer guidance when alternate nailers or no nailers are to be utilized. Pages 24 and 25 provide additional guidance on non-wood nailers, and the attachment of fasteners into light weight concrete and gypsum decks. A hidden component in an assembly that may carry a significant amount of load transfer responsibility, the design of this component should not be overlooked.
The single ply roofing industry continues to see advancement in masonry fastening solutions which can often eliminate the nailer altogether and allow for secure attachment of termination components without the use of wood. Care must be taken to assess the integrity of the masonry substrate, often a pull test of the existing condition is performed. In many external envelope strategies, designers incorporate air space, EIFS, and ACM panels which may create difficulty for proper securement of roofing membrane if not addressed during design. These variances may reduce the effectiveness of tested fastening patterns, and could create additional opportunity for torque failure from longer screws or nails improperly secured in an attempt to accommodate surfaces which may not be adequate for load transfer and securement.
As the design industry moves towards continuous insulation and building envelope solutions with continuity, many nailer alternates offer designers the ability to extend insulation or lightweight concrete beyond where traditional wood nailers have stopped these components in the past.
As we continue to strive for continuity in load transfer, continuity in insulation, and proper roof to wall transition, don’t overlook the hidden detail of your nailer, and the continuity and importance of this vital detail.
Brad Van Dam
VP of Sales
Click here to download the ANSI/SPRI ED1 standard and learn more about how you can participate in SPRI’s development, research, and industry advancement efforts in the Single Ply Roofing industry to help protect life and property.