How to Shim a Door in 7 Steps

Shimming a door is a pretty straightforward job, but you do need to make sure you have the right kinds of shims before you get started. For most residential applications, you can use wood or plastic shims, which you can pick up for just a few dollars online or at your local home improvement store.

If you’re shimming a fire-rated door—you might have one leading into your boiler room or your garage, especially if you have solar batteries or an oil tank in there—then you should opt for metal shims, which are non-combustible.

If you’re removing a door and installing a new one in your home, you should first get the new door frame centered in your rough wall opening using shims.

Start by getting the door roughly centered in your opening with the door closed. Depending on how your wall opening is framed, you should have anywhere from 1/4 of an inch to 1 inch of space on all sides of the door frame. Once your door is in place, insert shims loosely around the edges to hold it there.

Always use shims in pairs. It might be tempting to push a single shim into a gap, but since shims are angled, doing so will cause warping in your door frame over time. Instead, use two shims facing in opposite directions to create a perfectly flat but adjustable spacing. Aim for shims behind each door hinge and at the bottom and top of each stile. You can add more to the top and middle of the lock stile for additional stability, but it’s not necessary.

Hold your level up against your hinges with the door closed. If they’re perfectly level, you can move on to the next step. In most cases, the door won’t be perfectly level, so you’ll need to make adjustments. This is especially true if you’re using this guide to fix a sagging door.

Where you make adjustments will depend on how your door is sitting in the wall opening. Make adjustments on the hinge side only, if possible.

• If the top of your door on the hinge side is too far toward the wall framing, lightly hammer in the shims behind your top hinge.

• If the bottom of your door on the hinge side is too far toward the wall framing, lightly hammer in the shims behind your bottom hinge.

Once you’ve made adjustments, check again to make sure the door is plumb.

Now that your door is plumb, you can adjust the shims on the hinge side of the door to get the spacing right and tighten the door inside the wall opening. Start with the top shim, and don’t hammer in the shims so much that your door shifts. Try to get the spacing on your hinge side about equal to the spacing on the opposite side.

Start at the top hinge, then work down the hinges, and finally tighten the shims at the top and bottom of the door.

Follow the same process on the lock side, and try to get equal spacing on both sides of the door. Again, don’t hammer your shims too far, or you’ll risk pushing your door frame out of alignment.

Start at the top of the lock side and work your way down.

If you placed shims above your header, gently hammer those in to snug up the shims. Driving them in too much will cause the header to bow downward, and it could cause issues with the door’s functionality.

Finally, drive screws or finish nails through the door frame, through the shims, and into the framing around it to secure the door in place. You should at least add nails or screws through the shims behind each hinge and on the top and bottom set of shims on the lock side of the door.

For a more professional and finished appearance, cover the screw or nail heads with wood filler and paint over it. You can also counter-sink your screws to hide the heads better.