by Richard on November 4, 2020

Hanging Heavy Garage Cabinets

Hanging wall cabinets for a garage is a lot different than what you may have done for a kitchen. Read on to see the background of how to do the job right!

Most storage projects for a garage workshop involve mounting cabinets, shelves, or racks. They come with instructions, but most of the time, those instructions tell you a way to do the install but not why. YOU SHOULD ALWAYS FOLLOW THE INSTRUCTIONS YOUR CABINET MANUFACTURER GIVES YOU. However, every install is a little different. If you understand the “why” you will catch situations where the instructions don’t give you enough info to do the job right. It’s all about the fasteners and what they screw into, so let’s start by looking behind the drywall.

What Are My Walls Built With?

Here’s where you need to start. Most garage walls are built with a wood stud construction. Not all, however. You might have steel studs, cinderblock, or poured concrete as a wall structure. You might even have some walls in your garage with one type of structure and other walls with another. Once it’s covered with drywall, it’s hard to tell. But the difference is critical to the type of fastener that needs to be used.

If you aren’t 100% sure what type you have you need to run a test on each wall that you will be fastening to. The easiest way is to use a stud finder (see below for instructions) to locate the mounting studs or straps. Then drill a small 1/8” or so hole into the stud. The first half inch or so will be drywall and the shavings ejected by the drill will be a fine white powder. Continue trying to drill at least another 1” to 1.5” into the wall. If you have wood stud walls, you will start to see wood shavings ejected by the drill and you will have no issue drilling a hole the full inch deep. If the drill hits something hard immediately after passing through the ½” drywall, you likely have a metal stud. You can either continue to drill through the stud looking for metal shavings or take a utility knife to cut a slightly larger hole and confirm the metal stud. If, on the other hand, you drill past the drywall and then enter ¾” or so of wood, followed by something very hard, you likely have a concrete wall of one sort or another. If you have metal studs or concrete walls, you are going to need to take a bit more care mounting anything heavy on those walls. Full directions for those will be the subject of a couple of follow-on articles.

Get Yourself a Stud Finder

Yes I know folks who are professional carpenters that can tap on the wall and find the stud; you and I can’t do that reliably. So, if you don’t have one, get a good stud finder.

Just a reminder what drywall can hide. Get a Stud Finder.

It will allow you to find the center of a stud the first time. If you drill a hole for a screw and just catch the edge of the stud, it’s going to feel fine until you roll the screw in and the edge of the stud breaks out. Now the screw just turns and will not hold any weight. Don't go cheap, get a good stud finder. See the link at the bottom of the article for one that works.

Wood Stud Walls

If your garage has wood stud walls, count yourself as fortunate. That is the easiest and most versatile situation to deal with. Still, you need to understand what you are doing. Perhaps you have mounted kitchen cabinets in your house before. This is very, very different because of the load a garage cabinet can take. Those kitchen cabinets likely got put into place with a few drywall screws into the wall studs. In the garage, however, we are talking about holding heavy tools, parts, and other storage. A typical 30” wide wall cabinet may be rated for a 200 pound load, and it won’t be unusual to see it loaded up to that. Let’s dive into the techy stuff for the moment to see what kind of a load that puts on the fasteners.

As you can see, there are two kinds of loads: shear which tries to slice the screw in half and tension which tries to pull the screw out of the wall. Recall that there are only two studs behind a 30” wide cabinet so let’s start by assuming two screws. If the cabinet weighs 200 pounds and it is held up with two lag screws into the wall, the forces would be 100 pounds of shear on each bolt (200 lbs ÷ 2). The tension, however, depends on the height of the cabinet and the placement of the loads inside. For a typical 12” deep cabinet that is 18” high, that tension load would be trying to pull the screw out of the wood with a force of 70 pounds per screw. Now you might ask, "why is there any tension force at all? Looks like all the force is straight down." Well, think what happens to a loaded cabinet if you loosen the top bolts. The top of the cabinet will move away from the wall, but the bottom stays where it is (rotates around the red dot on the figure above). That's because the heavy loads sit on a shelf that is away from the wall. It causes the whole cabinet to rotate as if it was the claw on a hammer, trying to pull those top bolts out of the stud. So, as it turns out, tension is the most important force you have to deal with in a heavy cabinet.

But, let’s talk about the easy one first, shear force. 100 pounds of shear is more than twice what a drywall screw can handle on a good day. Never ever mount heavy cabinets with drywall screws. With those types of loads, and allowing a proper safety margin, you need to use a minimum of a ¼” lag screw.

One more note of caution; if you can’t find the studs (or they are not where you want them to be), you may be tempted to use fasteners that just screw into the drywall and not the studs like mollys, toggle bolts, or plastic inserts. In a word, don’t. You are way beyond the safe load carrying capacity of not only the fastener, but of the wallboard itself (don't pay any attention to what the guy says in the hardware isle of the big box store). Someone will get hurt.

On to tension loads. This gets tricky because it not only depends on how the manufacturer has designed the mounting and the height of the cabinet, but it also depends on the type of wood and strength of studs buried in the wall. Let’s assume the cheapest wood studs. Let’s also assume the cabinet has a series of holes punched in the back panel to line up with the wall studs. Most often that means the holes only allow one screw in each stud and therefore you would have two studs behind a 30” cabinet.

If the cabinet only has holes along the top, that means two lag screws. If it also has holes along the bottom of the cabinet, by all means use them since they help with the shear load, but understand that those bolts don’t help with the tension load in any real way. If that seems counterintuitive, remember what happens to a loaded cabinet if you loosen the top bolts. The top of the cabinet will move away from the wall, but the bottom stays where it is. However, the lags on the cabinet bottom will help to keep it in place if it gets hit from the side. So, whether you have two or four lag bolts in a 30" cabinet, the numbers in our example hold; ¼” lags will be fine. However, allowable tension loads also depend on how far the threads of the screw extend into the stud. As a good rule of thumb, the ¼” lag needs to be at least 2 ½” long, so counting a ½’ for drywall, you will have 2” of thread in the wood to carry that load. You can go longer to provide more safety margin if you want, but note that anything longer than 3 ½” and you risk ruining the wall on the other side.

If The Cabinet Holes Don't Line Up With the Studs?

Some cabinets don't have rows of slotted holes along the top. Instead, they have two or three holes, and if that's the case, you will often find those holes are not where they need to be. The easiest fix is to drill holes in the cabinet in the right places for your stud layout. One note of caution, however. If the holes in the cabinet are reinforced with extra structure (thicker metal of any sort), you will need to compensate in some fashion. Washers on the lug screws may be enough, but it is best to contact the cabinet manufacture for their advice.

Final Notes

Some cabinets will use brackets that get bolted to the wall first, and the cabinet drops into a groove on the bracket. In general, the rules are the same: use a minimum of ¼” x 2 ½“ lag bolts to fasten the brackets to the wall. If the brackets allow, use 4 lags for safety.
Always predrill the holes for the lag screws. It greatly improves the allowable tension load and helps to avoid cracking the stud. For a ¼” lag, use a 3/32” drill. For a 5/16”, use a 9/64” drill. For a 3/8” lag, use a 11/64”. Don’t cheap out on this; go get the right size bit. Too big or too small can dramatically impact the load carrying ability of the lag screw.
Always use a bar of soap to lubricate the threads of the lag screw before you run it in. If you are not used to doing that, you’ll be shocked at how much difference that makes in the effort to run it in.
Installing cabinets by yourself? Try screwing a 1" x 4" board to the wall right where the bottom of the cabinet is supposed to be. Drywall screws are fine for this since it is temporary. Resting the cabinets on that board makes it a lot easier to run the lag bolts in where they are supposed to be, and it ensures the tops of adjacent cabinets line up. Remove the board when all of the wall cabinets are in place.