There’s a lot to think about when selecting fasteners for a cold-formed steel framing system. What matters most are the screws and materials you select as well as the thickness of the members.
What fastener you use changes due to the style of wall, roof, and floor under construction. According to experts, bolts are seldom used with a cold-formed steel framing assembly. When they are used, it’s with truss configurations. Anchor bolts are attached to sill plates, hold-downs, or joists to foundations. Although welding can be used, they tend to appear in controlled conditions including panelized construction.
You’re going to be using screws more often than not because they’re easiest to use. Still, the type of screw you select for the job relies on specific application.
If you’re building an interior wall using cold-formed steel framing on a gypsum board, then the fastener choice relies on the style of the head. A bugle-head screw is constructed to countersink into specific materials including gypsum board. This screw connects the cold-formed steel framing and the drywall securely without damaging exposed surfaces of the drywall paper.
However, if the assignment is to frame the walls, and the cold-formed steel framing isn’t cover with another including drywall or sheathing, use hex-head screws. If drywall or sheathing will be applied later, then it’s best to use pan-head screws or other low-profile head types.
Materials Being Joined
If you fasten sheathing to cold-formed framing system studs or track, then the fastener you choose will change depending on the materials being joined.
Fastening rigid material like plywood or oriented strand board to cold-formed steel framing system that features studs or joists required a fastener head that lies flush with the sheathing. So, the best choices are bugle or wafer-head style screws. Be sure that the self-drilling screw threads penetrate the cold-formed steel-framing element securely. According to the AISI S200 standard, three threads should be exposed for a good connection.
Keep in mind that if you’re considering the use of self-drilling screws with reamer wings or tabs on the shaft between the threads and drill points, the wings ream a clearance hole in the plywood or other rigid material and keep the threads from engaging too soon. If connected too early, then there could be a separation of the fastened material from the base material. Once the tabs penetrate the wood or sheathing, they will break off allowing the threads to engage the steel.
If you’re assigned to fasten a cold-formed framing system with studs to a cold-formed framing system with a track, then x-bracing and gusset plates are required and the screw choice depends on the thickness of the cold-formed framing members.
Connecting steel to steel involves a fastener head with some bearing surface on top of the material being engaged. A hex or pan head screw would suffice. To achieve this you will need an electric screw gun with its nosepiece removed as well as some locking clamps. The clamps assist in reducing space between fastened parts and prevent movement during installation.
Thickness Of The Material In The Assembly
Self-piercing screws suffice with thinner materials including nonstructural cold-formed framing with studs (less than or equal to 0.033-inches thick steel). On the other hand, self-drilling screws suffice when piercing into thicker, structural cold-formed framing. Other styles of appropriate tapping screws include thread-cutting, thread-rolling, and thread-forming screws. Keep in mind, however, that these screws probably won’t be used in construction applications because many of them require pre-drilled holes.
When choosing the proper fastener for the job, consider the thickness of the material in the connection.
For example, if the thickness of the material is 33 mil steel or thinner, then use self-piercing screws. These screws can penetrate metallic material, expands a sleeve into the pierced hole of the steel sheet, and forms its own mating threads when driven.
If the cold-form framing system is thicker than 33 mils, then select a self-drilling screw. These screws feature a point that resembles a drill bit, so they can cut their own holes. The threads then tap their own internal threads without deforming or fracturing them.
Self Drilling screws have 5 Standard Drill Tip Lengths available. The length of the drill tip must be long enough to penetrate the base material before the treads engage the base material. If the threading action begins while the drill point is still drilling, the screw will most likely shear at the top of the threads where the threads meet the shank or at the head of the screw. This is due to the different speeds the screw is turning at the drill point versus the speed of the threading action.
Therefore it is imperative that you choose the proper Drill Tip for your job!
Standard Drill Tips are numbered from #1 thru #5
#1 & #2 Drill Tips are short & designed for 2 pieces of thin metals being fastened together (ie. 2 pieces of metal decking of 18 to 20 gauge material being stitched together.)
#3 Drill Tips are good for fastening materials to base metal of ¼” & under (ie. Fixture with pre-punched or drilled holes to ¼” steel)
#4 Drill Tips are designed to drill thru base metals 0f 3/8” & under (ie. Heavy gauge metal deck to 3/8” thick joists.)
#5 Drill Tips are THE BIG BOYS of the metal fastening industries!
These screws have a Drill Tip long enough to drill thru ½” thick steel. These screws more often are made with a fine thread to reduce friction & heat buildup when penetrating thru heavy steel!
Pick the right screw for your job & you will finish your project without hiccups!!!