Heavy Duty Drywall Anchors Weight Capacity
Without drywall anchors, our homes and businesses would look quite peculiar and drab without the many frames, décor, and other items that adorn their walls. Though the introduction of drywall has led to reduced material and labor costs and lower home prices, drywalls alone are not good at supporting the weights of objects that are mounted to them. This is because nails or screws driven through drywall can easily slip out with just a few pounds of weight. While lighter objects such as calendars and small décor can be successfully mounted to drywalls with nails or screws, what about larger objects?
Drywall anchors – special fastening devices that allow items to be mounted to walls without the need for studs – are the answer and were introduced to safely and secure heavy items to drywalls. In this article, we dive deep into what exactly drywall anchors are and how they work and discuss vital information regarding the different loads on both drywall and drywall anchors.
How do Drywall Anchors Work?
Different types of drywall anchors have different methods of securing into drywall. However, all drywall anchors work by gripping the drywall one way or another. By doing so, anchors can counteract the weight of a hung object safely. First, a pilot hole with a diameter that is recommended by the drywall anchor manufacturer is drilled into the drywall at the desired location. Then, drywall anchors are placed into or through the pilot holes. Once placed, screws can work with the anchor to create a secure connection, whether that is through the expansion of the anchor within the wall or by forming a clamping force between the anchor and the installed object.
Rule #1: Always Look for a Stud
When mounting heavy objects, it is always preferable to screw at least 1” into a stud. If you can find at least one stud to use for mounting an object, you can be assured that you have a secure, reliable connection.
If you’re mounting something heavy and can’t find a stud, think about using a wood backing behind the drywall or adding a simple wooden mount that connects between two studs. All of the above do not require a drywall anchor.
Although drywall anchors are a convenient solution, using drywall anchors can be dangerous and cause serious injury if not used or installed correctly. It’s important not to surpass the recommended weights for drywall anchors when mounting objects. If you ever have doubts or reservations that a particular drywall anchor can support a specific weight, then consult with a professional. This article is presented for informational purposes only, and should not be used to exceed manufacturer recommendations.
Important Load Considerations When Using Drywall Anchors
While it can be easy to install drywall anchors, hang objects, and call the job done, it’s important to have an understanding of the different loads that act on an anchor when an object is mounted. By doing so, you can be more aware of the potential pitfalls of using drywall anchors and ensure safe usage every time.
When objects are mounted onto a drywall anchor/screw assembly, two main forces are developed: tensile and shear forces. Tensile forces are forces that act parallel to the shank of the screw and cause the screw and anchor to be pulled from the wall. Shear forces are forces that act perpendicular to the shank of the anchor and pull downwards. For objects mounted flat onto walls via a drywall anchor, the weight of the object is the shear force. If you mounted a hanging plant on a straight hook, there will be a tension force trying to pull it out of the wall. When evaluating the loads on an anchor, assess each force by itself.
While this discussion only considers simple loading, load analyses for drywall anchors can quickly become complicated with distributed loads or loads applied at noticeable distances from the wall. Listed below are two key considerations when using drywall anchors:
1. Shear Forces
Shear forces are normally accounted for by the weight of an object. If an object is too heavy, it may dig into the drywall and enlarge the bottom opening of the hole. Depending on the type of anchor, this may create a situation where you find the anchor easily slips out of the wall. If you’re using a wall anchor that relies on a tight fit within the hole you drilled, you just lost much of your holding power. Typically advertised weight ratings will incorporate a safety factor, but even so, it is always best to work below the rating. This helps account for imperfect installations and unexpected, variable loads that may be placed on the object you’re mounting.
Consider using multiple drywall anchors to evenly distribute heavy loads amongst them so long as the partitioned load is still lower than the manufacturer’s recommendation. Be mindful of the placement of drywall anchors as placing them too close to each other or using an excessive amount of drywall anchors can actually compromise the strength of the drywall. Although you may come across data that shows ultimate load capacities for your anchor type, without perfect knowledge of testing conditions and your own materials you’re working with, don’t assume they are directly applicable to your installation.
2. Cantilevers and Tension
A cantilever is a structure, typically a beam, that is fixed and supported on one end while a load is applied on the opposite, free end. When an object is mounted at a distance from the wall, the drywall anchor/screw assembly effectively functions as a cantilever. Hence, torque is developed on the fixed end of the anchor that can pull the anchor out of the wall if loads are too high.
The weight distribution of a hung object can have a big impact on the forces experienced by the anchor. A common use for drywall anchors is to hang floating shelves or plant hanger hooks. These usually have items placed along the same axis as the anchor. For shelves, all you need is for one of a pair of anchors to be improperly installed for undue stress to be placed on one side of the mount. Therefore, the entire assembly can act as a cantilever. Objects placed on the end of the shelf or hook can create a “crowbar effect” in the drywall anchor which could rip the anchor out of the wall.
It’s recommended to distribute weights evenly between the wall and the edge of a floating shelf to prevent this effect. This is because distributing the load actually produces less torque at the wall which can be proven through an engineering static analysis. Consider using L-shaped brackets with drywall anchors to help bear some of the load and prevent the crowbar effect, too.
Will the Drywall Anchor or Drywall Fail First?
Drywall anchors have a max load that they can experience before failure. But what about the drywall?
According to the Gypsum Association, the flexural strength of various drywall types and thicknesses was found to be between 50-100 lbf, depending on the type and thickness of the drywall. Drywall samples were tested in accordance with ASTM C473. In this test, a horizontal piece of drywall is fixed while a testing apparatus pushes down on the center of the drywall to make it flex and eventually break. Additionally, the nail pull-out resistance in drywall was found to be anywhere between 40-100 lbf, depending on the thickness of the drywall.
If you’ve ever taken a close look at the test data for a particular type of drywall, you may notice that the flexural strength varies depending on whether it is installed parallel (vertically) or perpendicular (horizontally) to the framing. When you take into account that you could be dealing with 16” or 24” stud spacing, you may find that drywall can be much stronger (or even much weaker) than you might expect.
Drywall anchors and the holes with which they are mounted are small relative to the size of an entire drywall panel. Because shear forces and moments created by drywall anchors are localized, the drywall should not fail so long as drywall anchors are installed properly and not too close to each other. It’s more likely you may have to contend with some localized crumbling due to variable forces placed on a particular anchor.
Drywall anchors are exceptionally useful fastening devices if they are used with an acknowledgement of their limitations. Our offerings include self-drilling anchors in diecast zinc or Nylon and toggle bolt assemblies. For more information check our latest guide How to Choose a Drywall Anchor to see which drywall anchor is right for your project.