Unless you install windows and doors professionally, you might not be familiar with shims. However, knowing how to shim a door is the secret to perfect alignment. These small wedges ensure your door frames are square so the door hangs straight and latches correctly every time.
In this guide, we share the best methods for shimming a door and break down the pros and cons of different shim materials.
Key Takeaways
- Purpose: Shims are tapered wedges used to square door frames within a rough opening, ensuring the door doesn’t stick or swing open on its own.
- Materials: Wood and composite (plastic) are the industry standards; composite is preferred for exterior use due to rot resistance.
- Placement: Install shims in pairs (opposing wedges) at hinge locations and behind the strike plate to create a flat, load-bearing surface.
- Installation: Always level the hinge side first, secure with nails or screws, and use low-expansion foam for extra stability before replacing trim.
What Are Door Shims?
Door shims are thin, wedge-shaped pieces of material used to fill gaps between the door frame (jamb) and the rough wall opening (studs). Because rough openings are rarely perfectly square or plumb, shims allow you to adjust the frame until it is perfectly vertical and level.
How Many Shims Per Door?
You typically use three to five sets of shims per door side. Critical placement spots include directly behind each hinge and behind the strike plate (lock side). Using pairs of shims at these stress points prevents the jamb from twisting.
Best Materials for Door Shims
Not all shims are created equal. Choosing the right material depends on whether you are working on an interior bedroom door or a heavy exterior entry door.
Wood Shims
Wood is the traditional choice. They are usually made from cedar or pine. Cedar is superior because it resists rot and pests better than pine.
- Pros: Readily available, easy to cut with a utility knife, inexpensive.
- Cons: Can compress over time; prone to swelling if they get wet.
- Best For: Interior doors and dry locations.
Composite / Plastic Shims
Composite shims are becoming the industry standard. They are molded from recycled plastics and often come with pre-scored lines for easy snapping.
- Pros: Rot-proof, water-resistant, high load-bearing capacity (won’t compress), easy to snap without tools.
- Cons: Slightly more expensive than wood; can be slippery to stack.
- Best For: Exterior doors, bathrooms, basements, or heavy solid-core doors.
Steel Shims
Steel shims are generally reserved for industrial applications or fire-rated commercial doors where combustible materials are prohibited. They are extremely durable but unnecessary for typical residential use.
Cardboard
Cardboard should only be used as a temporary spacer or for very lightweight interior adjustments. Never use cardboard for exterior doors or heavy loads, as it compresses easily and disintegrates when exposed to moisture.
Door Shimming Diagram and Logic
Image: (Please use hinge-shim-fig-1 attached in Trello card).
Shims solve various alignment issues. Whether your door hits the jamb, won’t latch, or swings open by itself (ghost door), shims can correct the angle.
Gap Too Big on Lock Edge
Image:(Please use door-gap-too-big-1 attached in Trello card).
If the gap between the door and the frame on the lock side is too wide, the latch might not catch.
The Fix: Place equal thickness shims behind the hinges. This pushes the entire door slab toward the lock side, closing the gap. You can also add thin cardboard shims behind the specific hinge leaf (between the hinge and the wood jamb) to micro-adjust.
Gap Too Small on Lock Edge
Image: (Please use door-gap-too-small-1 attached in Trello card).
If the door rubs against the frame near the latch, the gap is too tight.
The Fix: You need to pull the door away from the lock side. Often, this means removing existing shims from behind the hinges to recess the hinges deeper, or ensuring the lock-side jamb is shimmed tightly against the stud to widen the opening.
Out of Square (Toe-Out)
Image: (Please use door-toe-out-1 attached in Trello card).
“Toe-out” usually means the door gap is wider at the bottom than the top.
The Fix: Shim the bottom hinge out slightly more than the top hinge. This pushes the bottom of the door toward the lock side, squaring it up with the top.
Out of Square (Toe-In)
Image: (Please use door-toe-in-1 attached in Trello card).
“Toe-in” is when the gap is wider at the top than the bottom.
The Fix: Add more shim thickness behind the top hinge. This kicks the top of the door over, aligning it with the bottom.
How to Shim a Pre-Hung Door
Shimming a pre-hung door is a straightforward process if you follow the “opposing wedge” technique. This method uses two shims facing opposite directions to create a flat, level block rather than a slanted wedge.
What You’ll Need
- Hammer and finish nails (or drill and screws).
- 4-foot spirit level.
- Pack of wood or composite shims.
- Utility knife.
- Pry bar (if removing old trim).
- Tape measure.
1. Prep the Opening
If replacing an existing door, remove the old trim carefully with a pry bar. Use a utility knife to score the paint line first so you don’t peel the drywall paper. Clean out any old nails or debris from the rough opening.
2. Check the Floor Level
Check the floor for level across the width of the doorway. If the floor isn’t level, you will need to cut the bottom of one side of the door jamb so the head jamb sits perfectly level.
3. Center the Door
Place the pre-hung door into the rough opening. Center it so there are roughly equal gaps on the left and right sides.
4. Plumb the Hinge Side First
This is the most critical step. Place your 4-foot level on the face of the hinge-side jamb. Adjust the door in or out until it is perfectly plumb (vertical).
5. Insert Shims at Hinges
Start at the top hinge. Insert a shim from the inside and a second shim from the outside (opposing wedges). Slide them against each other until they fill the gap snugly without bowing the jamb.
Repeat this process at the middle and bottom hinges. Constantly check your level to ensure the jamb remains plumb.
6. Secure the Hinge Side
Once the hinge side is plumb and shimmed, drive nails or screws through the jamb and shims into the stud. Place fasteners behind the weatherstripping to hide the holes.
7. Shim the Lock Side
Move to the lock side of the door. Close the door and inspect the gap (reveal) between the door slab and the jamb. It should be consistent from top to bottom (usually about 1/8 inch).
Insert shims behind the strike plate and near the top/bottom to maintain this consistent gap.
8. Secure and Insulate
Nail or screw the lock side through the shims. Once secure, test the door swing. It should open and close smoothly without binding.
Pro Tip
Before replacing trim, apply low-expansion window and door foam in the gaps. This locks the shims in place and provides insulation.
9. Trim the Excess
Score the protruding shims with a sharp utility knife and snap them off flush with the drywall. If using composite shims, they often snap cleanly without scoring. Reinstall your trim to cover the gap.
FAQs
Do All Doors Need Shims?
Yes, practically all framed doors need shims. Rough openings are rarely perfectly square or sized to the exact millimeter of the door frame. Shims bridge that gap to ensure the door hangs plumb and operates smoothly.
Can I Use Cardboard As a Shim?
You should avoid using cardboard for structural shimming. It compresses easily and falls apart with moisture. Only use it for very minor, non-structural adjustments, such as behind a hinge leaf to fix a slightly binding door.
What Is the Correct Way to Insert Shims?
The correct method is the “opposing wedge” technique. Insert one shim from the front and one from the back, with the tapered ends overlapping. This creates a flat, parallel surface that supports the jamb evenly without twisting it.
Do You Screw Through Shims?
Yes, you must drive your fastener (nail or screw) through the jamb, through the shims, and into the framing stud. The fastener locks the shims in place so they don’t slide down over time.
How Do You Shim a French Door?
Shim a French door exactly like a standard door, but pay extra attention to the header. Since two doors meet in the middle, the top gap (reveal) must be perfectly even, or the doors will look crooked when closed.
Wood vs. Composite Shims: Which Is Better?
Composite shims are generally better for modern construction. They are rot-proof, impervious to water, and snap cleanly. Wood shims are cheaper and fine for dry interiors, but composite is superior for exterior doors or bathrooms.
Shim It to Win It
Shims might look like scrap wood or plastic, but they are essential engineering tools for your home. Without them, hanging a door correctly is nearly impossible. By taking the time to level your jambs and use the opposing wedge technique, you ensure your doors latch with a satisfying click for years to come.
Next time you have a sagging door or a sticky lock, grab a pack of shims and get that frame square.
