Fastening Tips for Attaching Metal Roofs

by Jonathan McGaha | 31 January 2016 12:00 am

Basic information to help select and install fasteners correctly

Fasteners are integral to the overall performance of metal roofs. It is important to understand the correct way to select and install a fastener to achieve the necessary uplift requirements and provide a leak-free roof. Using the wrong fastener or installing it incorrectly can cause the roof to fail.

 

Selecting a Fastener

The fastener is a very important component to how well the roof system performs. Take great care in selecting a fastener that meets the minimum design loads, and use fasteners specified by the panel manufacturer or design professional to achieve optimal performance.

Identify the substrate. Identifying the material type and its thickness will allow you to select the best fastener for the substrate. For instance, self-drilling screws used to attach to steel have particular point types that perform in a specific thickness range. Thin connections like panel laps require a small drill point like a DP1 type, and structural connections utilize up to a DP5 for attaching up to 1/2-inch-thick steel. Follow the screw supplier’s recommendations for attaching to your particular substrate.

Load requirements. One of the most important functions of the screw is to secure the metal panel so the roof or wall system achieves the minimum load requirements. Screws must meet particular specifications for pullout, pullover and bending. Take care to analyze the connection and select the appropriate screw that meets all of the load requirements.

Environmental issues. The environment effects the corrosion resistant of the screw, and you should select a fastener that meets your corrosion expectations.

For exterior applications, choose a long-life coated screw, long-life head screw (stainless steel or zinc), or a stainless steel screw. It is always best to select a fastener that is compatible with your panel. To help in your selection, Pittsburgh-based Triangle Fastener Corp. and the Metal Construction Association (MCA) publish a fastener selection guide for attachment of various types of metal roof panels. Refrain from using ordinary zinc-plated screws for exterior application unless they have a minimum of 0.0005-inchthick zinc. Thinly coated zinc plated screw can rust quickly in normal weathering conditions.

Attachment length. Determine the overall length of the materials and include any space between the materials. Select a fastener length so that full threads engage the substrate.

• For steel substrates, make sure at least three full threads extend beyond the bottom of the substrate. This will ensure that complete pullout load is achieved.

• For wood substrates, select a screw length to embed full threads into the deck; or a minimum of 1 1/2-inch embedment into the wood structure.

Tools and Fastener Installation

Using the correct tools and installing the fastener correctly will ensure the connection performs as specified.

Screw guns. Using the appropriate screw gun type and rpm will produce better screw performance and reduce the chance of screw failure caused by improper installation. We recommend using screw guns with the following features:

• Screw gun should have a depth sensing or torque control feature to ensure you tighten screws to the optimal level.

• Use a variable speed screw gun. This will allow you to adjust the speed to accommodate for varying hardness of steel or inconsistent thicknesses.

• For steel substrates less than 1/4-inch-thick and wood: Use a 2,500-rpm screw gun.

• For steel substrates one quarter-inch or thicker Use a 2,000-rpm screw gun. This will reduce the chance of point burnout caused from excessive heat created during the drilling of the screw. We do not recommend using impact tools for installing self-drilling or pancake head screws. This type of tool can exceed the strength of the screw, causing it to fail. They can also damage painted surfaces and strip-out screws.

Drive sockets and insert bits. The use of high-quality nut-setters and insert bits will aid in the installation and improved performance of the fastener. Poor fitting sockets and bits cause the screw to drill poorly and damage painted heads. Here are a few tips that will assist you during installation:

• Set the magnet located in the nut-setter so that you fully embed the hex of the screw. You can fully embedded screw hex by inserting a screw into the nut-setter, and hammering the screw tip until the hex of the screw is fully embedded. This will improve the drivability of the screw and eliminate wobble.

• Holding the screw gun perpendicular to the surface will allow the screw to drill and tap effectively. Be sure the fastener completes all the drilling before thread tapping occurs. This will eliminate jacking of the panel and point failure. Do not apply excessive pressure during installation. This can cause the fastener to fail due to excessive heat caused during installation.

• Tighten screws with sealing washers so that the EPDM sealant extrudes to just beyond the outer edge of the metal backing or flange. This will ensure a leak-free seal.

Joe Stager is vice president of Triangle Fastener Corp., Pittsburgh, and has more than 38 years of experience in the fastener industry with management positions in designing, manufacturing, selling and marketing fasteners to the industrial, automotive and construction industries. To learn more, visit www.trianglefastener.com[1].

Source URL: https://www.metalconstructionnews.com/articles/fastening-tips-for-attaching-metal-roofs/

---