Working With Wood Shims
DEAR TIM: I need to install some doors at my house. I've never done it before. A friend told me to make the rough opening that the door and frame sit in larger than the actual door frame dimensions. This seems odd to me. He also told me I need to use shims to help install the door. What are shims and how do they help you install a door? Are there any best practices to follow when working with shims? Paula G., Seymour, IN
DEAR PAULA: The good news is your friend is giving you some solid advice. I would continue to accept advice from this person as he/she seems to be in the know. Installing a door is not as easy as you might think, and it's impossible for me to convey all the necessary steps in this short column.
Let's talk first about rough openings and why they need to be larger for both doors and windows. It's imperative that doors and windows have minimal or no structural stress or pressure applied to them at any point while they exist in your home. If you installed a door or window in a wall and it was tight against the rough framing lumber on all sides, loads could easily be transferred to the door or window causing it to rub, stick, not open or close properly, etc.
The gap between the rough framing and a door or window jamb that's created when you create a larger rough opening allows for the stress and loads to be transferred around the door or window. The gaps also allow you to make the fine adjustments to the window or door so they operate and fit perfectly for years and years. You can also install insulation and flashings in the gaps to make the openings both air and water-tight.
The gaps between the outer edge of the door or window jambs and the rough framing should rarely, if ever, be more than one-half inch. Some door manufacturers want the gap to be no larger than 3/8ths of an inch. Read the written instructions that come with your doors.
Wood shims are used to make the door or window fit tightly in the rough opening so it does not shift around when the door or window is operated. Shims are flat pieces of wood that can be anywhere from 6 to 10 inches long and have a taper to them. One end of a wood shim is normally about 1/16th-inch thick while the other end is about 3/8th-inch thick. A shim is normally about 1 and 1/4-inch wide.
Wood shims can be made from any wood species, but I really prefer to use those made from cedar. They're easier to work with and easier to trim with a razor knife. You'll frequently run across packs of shims made from yellow pine. These are extraordinarily hard to work with and trim. Once in place you generally have to cut yellow pine shims with a sharp wood chisel and hammer.
When shimming a door in position, it's usually best to start on the hinge side of the door. Most manufacturers want to see shims at the same height as the hinges on the door. Putting the shims at this location is really the right thing to do as the weight of the door is transferred to the door frame at these points. You want the door frame snug and tight against the rough opening at these points so the door doesn't move over time.
Shims are generally installed in pairs one shim coming from each side of the door jamb. You slide each shim towards the other one so the thickness of the two shims increases at the same rate to fill the gap between the door frame and the rough opening. If you just shove one or two shims from the same direction, you'll have a triangle of wood between the door frame and the rough opening.
You want a solid connection between the door frame and the rough opening with no gaps. If the rough opening is twisted because the lumber is warped, you may have to install an extra single shim to completely fill the gap.
I feel it's best to install trim screws immediately below the shims that pass through the door frame and then into the rough framing lumber. You want the fasteners to penetrate into the rough lumber at least 1 and ½ inches. If you drive the screws through the shims, you'll discover it's impossible to move them to make tiny adjustments as you install the door.
By placing the screws immediately below the shims, the shims can't fall to the ground as you work with the door.
Try to keep shims dry at all times. If the shims get wet and you use them while they're wet, they undoubtedly shrink when they do dry. This shrinkage could cause the door or window to not fit properly at a later date.
If the rough opening is too big, meaning it's more than 1 inch wider than the actual overall width of the door frame, you should add solid lumber to the rough opening to reduce the width. It's a good idea to shim this additional lumber in multiple locations so the rough opening is absolutely plumb.