How to Fix a Door That Lets in Light

Light coming through the gaps around a closed door means the door isn't sealing properly. This is a problem for bedrooms, home theaters, darkrooms, and anywhere you need darkness or privacy. Here's how to seal it completely.

Why Is Light Coming Through My Door?

• Worn or missing weatherstripping: The seal around the door stop has compressed or fallen off
• Gap at the bottom: No door sweep installed, or the existing sweep is worn
• Door doesn't fit the frame: The door has shrunk, warped, or the frame has shifted
• Hinge side gap: Hinges not mortised deep enough, pushing door away from frame

Step 1: Map All the Light Gaps

Close the door and turn off all lights in the room. Let your eyes adjust for 30 seconds. You'll see exactly where light is entering — mark each spot with tape on the frame.

Step 2: Seal the Bottom Gap

The bottom gap is usually the largest source of light. Install a door sweep for a complete seal.

• GroTheory Door Bottom Sweep 2-Pack (39") — seals the full bottom gap; blocks light, drafts, and noise

Step 3: Replace Weatherstripping on All Sides

Apply new weatherstripping to the door stop on all three sides (top and both sides). The foam compresses when the door closes, creating a light-tight seal.

• Foam Weather Stripping Seal Tape 16ft (1/2" x 1/4") — high-density foam, self-adhesive, apply to door stop for complete seal

Step 4: Fix Hinge Depth if Needed

If light comes through the hinge side, the hinges may be sitting too shallow, pushing the door away from the frame. Add hinge shims to push the door back toward the hinge side.

• Door Hinge Shims 10-Pack (0.040") — add behind hinge leaves to close hinge-side gaps

Step 5: For Maximum Light Blocking (Bedroom/Theater)

For complete blackout, combine:

• Door sweep on the bottom
• High-density foam weatherstripping on all three frame sides
• Door frame gasket or bulb seal for the most complete seal
• Consider a door draft stopper on the inside for extra bottom coverage

Step 6: Check Door Alignment

If the door doesn't sit flat against the door stop on all sides, fix the alignment first. Tighten hinges, add shims, or plane the door edge as needed before applying weatherstripping.

How Much Weatherstripping for a Full Door?

A standard 80" x 36" door needs approximately 16 feet of weatherstripping to seal all four sides including the bottom sweep. Buy a 16-foot roll and a door sweep together for a complete kit.