Recently was involved is a discussion about hanging cabinets and noted that some do not know how this it to be done in a safe manner. Hung wrong on a wall is a dangerous situation in a home, business or shop and anyplace where people may be walking, standing or seated. It my post in reference to a question I wrote about how a lady was severely injured when her new recently hung cabinets fell off the wall and landed on top of her. This could have been much worse than it was as it could have killed her. Had it been a child it most likely would have as the cabinet would have hit the child in the head. As it was the lady was tall enough that he cabinets hit her at the level of just below her shoulder and it fractured the large bone of the arm and bruised her pretty bad all the way down to her knees. The cabinet run was about 8 feet long and 12 inches deep and about 36 to 38 inches high. It was filled with dishes causing the cabinet to be pretty heavy. The failure of the cabinet installation was when the company installed them using long dry wall screws of which many of the few that they screwed into the cabinet missed the wall studs.
In order to properly install an upper cabinet to the wall, the cabinet must first be built correctly. It should be built with at least a 1/4 " thick back of which it should be properly applied to the back. The material to build the cabinet carcass should be of quality material and should be build using 3/4" thick material. This would be for the top sides and bottom as well as any interior panels. All joinery should be glued and screwed or other wise firmly attached with the end cut to the length of the desired finished height and the top and bottom then glued and attached with screws or other suitable fasteners. I build mine using all pocket screws hiding the screws from sight by boring pocket holes to be located on the top side of the top and the bottom side of the bottom. All inter panels are screwed and glued by driving the screws upward from the bottom and downward from the top. This hides the screws the best. Before assembly of the cabinet box you should cut a 1/4 inch deep rabbit along the inside (inside of the cabinet) The rabbit should be cut 1/4 inch deep and 3/8 of an inch or half the thickness of the 3/4 inch thick panel. Now do the same thing on the two side panels but make the rabbit the full length of the panel. (This rabbit is for the rear 1/4" thick panel that will be added.) There is not rabbit cut in the top panel (top of the cabinet as the top will extend out covering the top of the rabbits in the end panels. Your 1/4" ply end of the back will then be covered by the top.
The top rear of the cabinet should have a hanging rail (aka cleat) that is firmly attached using glue and screws. It should be made of 3/4" thick material and 4 inches wide. ( I use the same hard wood that I will making the face frame out of) It is inset a total of 1/4 inch in from the back edge as I will be using a 1/4 inch think back panel of which I will add to the cabinet back. This makes the cabinet back flush to the wall. The hanging strip or cleat should be glued and screwed to the top every 6 to 8 inches apart and at least 2 screws on each end. Placing the screws on the back side of the hanging rail will hide the screws when viewed from the front of the cabinet.
When cutting the interior panels these will be cut 1/4 " less in width than the end panels and the top as this allows you to pass a 1/4 " thick panel over the inter panels allowing you to use a single continuous panel across the back. You will need to also cut the the bottom 1/4" less than the side and top panels. There are two schools of thought when installing the inter panels as you either have to make a cut out for upper hanging rail in the inter panels or cut the hanging rails to fit between each inter panel. Both work well as long as you secure the hanging rail secure to the inter panels. My usual choice it to make the cut out to go around the rail and attach the rail as one continuous piece and drive a screw through the back of the rail and into the back edge of the panel. This is a harder method as you must be precise in cutting the fit for the rail in the panels. [Assembly of the cabinet is done by keeping all of the members flush at the front.
When this is done you will now have a cabinet box of which is strong and will remain square after it is built. You need to square the cabinet box up when adding the back panel as the panel will be inset into the rabbits you cut earlier. This will make a rigid and strong cabinet and will keep it square. Do not attach the panel at this point.
To determine the length of the rear panel ( cabinet back) it is simply the distance from the inside of the top panel of the cabinet (top) to the bottom edge of the side panels. As an example it is 37 1/4 inches on a 38 inch high cabinet so you would cut the panel to 37 & 1/8 inches long. This causes the panel to extend down past the bottom of the bottom panel but 1/8 less than the side panels.
Now it is time to cut a lower hanging rail of which is also a hardwood so it looks finished on the outside. The length is the width of the inside between the two side panels and the width is the amount that the side panels extend down past the bottom of the lower panel. Glue and screw this piece to the cabinet bottom but also set in to the inside edge of the rabbit. Now you can square up the cabinet and attach the rear panel using glue and fasteners. (I use a fine wire stapler and attach the back at all locations where a fastener can be inserted without showing.) The reason for the panel being 1/8 less that the 37 1/4 inches is to hide the bottom of the plywood however In most cases it will not matter as a back splash is usually enough to hide the almost inviable seam.
This is one method of building a cabinet using pocket holes and screws. I also use a second method and it is by cutting tongue and grooves in all the members and using glue and pins to hole the members tight until the glue cures and also by using as many screws that I can and still hide them. I do this on the router table using a special bit set. The hanging strip is done the same way. It is this upper hanging strip that secures the cabinet to the wall studs and the lower one secures the cabinet to the studs at the bottom and keeps the cabinet bottom tight to the wall. Now that you have built a well constructed cabinet carcass now installation time begins.
The hanging of a cabinet is simple but a critical step in making sure that they stay on the wall and hold the load that is placed in them. Simply adding a baton to the bottom of the cabinets and adding a few screws at the top is really not a safe method and to be honest with you it looks rather un-professional even if it is in a garage or on a back porch. It will make even the best looking cabinet look like trash.
In a wall with the 16 inch center spacing is going to be the easiest to hang the cabinets in but the ones that only allow you to place one every 24 inches will change the total picture of how you are going to hang them and still have a safe and secure installation. Installation of a cabinet run on a wall with 24 inch centers can be safe providing that there is more than one or two studs available in which to install screws through. It is important that the ends of the cabinets be secured as well as the center portion of the cabinets. This means that it will depend on the length of the cabinet run as to how many screws you should apply. There is also things encountered in cabinet installations that will cause you some difficulty in how you are going to hang the cabinets. Things like bowed walls, both looking at the wall vertically and also horizontally . A wall the in either bowed inward or outward at the point where the cabinet top meets the wall is going to cause you some troubles. Depending on how severe the bow is can alter your plan. A wall that is bowed enough to hold the cabinet off the wall more that 1/4 inch will need some special attention to it installation. A bowed inward at the middle area of the cabinet will require shims to make sure the cabinet is tight along the wall and the same thing applies to inward bow at the ends of the cabinet. An outward bow presents a different scenario as to how you are going to hang the cabinet. It depends on what is causing the bow and how severe it is.
Tricks to fix a outward bow in a wall includes simple things like shaving the wall at the bow as well as shaving the cabinet down. It does have its limits and some have been so severe that I have actually had to remove the drywall at the location where the cabinet is going to be installed and repair the framing by adding studs in a bearing wall as well as shaving back the studs. You find this is old buildings as well as new ones and some are more severe depending on not only the skill of the framers or the finish plaster man but on homes that are build in the winter and not properly allowed to dry out between the framing process and the finish plaster or dry wall installation. The lumber is soaked and covered when it is still soaked with give you a wall that is ever changing and causing nail pops and walls the change day today until the water is finally dried out and the wall studs become stable. This is also where a lot of mold in new construction begins.
This is why it is most important to visit the site of the installation even before you start building cabinets for it as it may change your method of building the cabinets. Beside taking a tape measure take along a camera, a 4 foot and an 8 ft level and a good framing square. Check the plumb of the wall and the level condition of the floor. Check the square of the corners and do both the plumb checking and squareness of the corners in several locations. This was you can get an idea as to what you are facing come installation time. Photograph the area and note any special points that you see that is going to become a critical circumstance in either the building of the cabinets as well as installation
If replacing cabinets this is also of importance. Take a look at the walls and how plumb is it and also how square if the wall. Use the square is as many places as you can. Take a good look at the existing cabinets and look for joints that have spread apart. Look for recent or old repairs that have been done to the cabinet. Look for a cause of the failure as it might tell you the story of the walls behind the cabinets. Check the run of the floors for how level are they. Take a general overall look at the cabinets construction. Is the back of the cabinets pulling away from the carcass. Do the cabinets sit plumb and level across the span of the cabinet run. Do the cabinets fit flat against the wall.
Consult with the owner of the cabinets and or the general contractor and point out any items of concern. There has been many times where I have had to build a cabinet altering the normal build. Such things have been over sized panels that allow scribing to the fit a wall . The building of a cabinet where you can fit a second panel on the ends where the eye can see such as between sinks and the ending run of a cabinet. I have had to build cabinets that had a deeper floor or bottom that the top and vise versa other wise build a cabinet that will fit the wall.
The addition of using a French cleat hanging system of which is best done if you build the cabinet to fit the French cleat and actually build the French cleat into the cabinet as you do not have to alter the cabinet to add the French cleat.
Well by now you have built the cabinets and should be ready to install them. Of great importance is the screws that you are going to use to mount the cabinets to the wall. The quality of the screw will depend how well your installation is and is it safe or unsafe or just marginally after you have finished the install.
Do not use things like dry wall screws to mount the cabinet. On the box it says "dry wall screws" so that is the only thing that they are good for. You need a screw that is not brittle and break easily when sheer load is placed on it. Of most importance is the tensile strength of the screw. It must resist the weight of the cabinet and the load in the cabinet, building stresses from movement and then the stresses that are placed on the cabinet by opening and closing the doors and drawers.
I use screws that are 2 & 1/2 inches long and the last inch of these screws have a bare shank. The thread are aggressive and highly resistance to pull out and the purpose of the bare shank is to allow the screw to pass through cabinet hanging rail and into the studs and allow the cabinet to firmly seat against the wall. Of importance is that the bare shank will spin in the cabinet rail and will not give you a false indication that you have hit a stud and not missing it and are getting the feeling of the firm seating of the screw from the threads still being in the cabinet member. These screws are made for installation of cabinets and not like deck screws or other types of screws that are not satisfactory for installing cabinets.
There many tricks in building and installing cabinets and I have only touched the basics. I will be glad to discuss additional tricks that my long time of doing this has taught me if anyone is interested. Just remember that the finest cabinet ever built will be like the worst ever built if it falls off the wall. Have a good day.