November 9, 2022

What to do when you have a gap under the door

Do you have a gap under your door? If so, you’re not alone! This is a common problem that many people face. In this blog post, we will discuss ways to fill the gap under the door. Filling the gap will help keep out the cold air in the winter and the hot air in the summer. It will also help keep out pests and noise!

How to fix the gap between the door and the floor

Use wood filler, caulk, threshold seal strip, fit casing, plinth block, and door jamb pieces, and prime and paint the gap between the jamb and floor. Calculate the distance to fit the pieces. Insert a threshold seal by cutting the threshold seal strip using a hacksaw, and applying it on the gap using strong adhesive glue to stick to the place.

Attach the casing part, cutting a piece of casing to fit inside the hole between the door jamb to the floor. Apply glue on the backside of the casing chunk and attach it to the gap. Hammer the surface 2 to 5 times.

Get the pull saw and rip the casing. Do not detach to insert the plinth block. Use an electric jamb saw to rip the casing overhead mould.  Cut your door jamb according to the gap measurement using a drill or wood trimmer for shaping. Add it to the gap and tap on it with a hammer. 

After placing the chunk, insert sealant or wood pieces to cover if there are still openings, Apply primer, paint, and sand down the surface, covering up any cracked surface using filler.  Primer down the surface and wait for 4 hours. 

Soak the brush over the paint, re-painting the surface for a natural look. Let it soak for several hours, then repaint the surface 2 to 3 times for full coverage. Dry the surface and complete the job.

Door gap filler vertical

Set the door into a rough opening and vertically level, filling any gaps at the sides with cedar shingle shims. Use sticky foam tape, tubular silicone, vinyl, rubber, or corner pads.

How much gap under the door for return air

The door undercut would need to be 1.5 inches or greater to allow enough air to pass.

How to fill the gap under the door trim

Insert a threshold seal. T-molding is a threshold that has a slight beveled or rounded top. The protruding edge centered on the bottom fills the gap between the door and the floors. Check to see if your door will close over it by placing a piece of it on the floor under the door. 

If the door works, measure the width of the opening and add the width of the casing. Cut the molding to size using a coping saw and clamp the molding to the end of a table. Draw the notches on the molding with a pencil. 

Trim the ends if needed by pulling the narrow blade of the coping saw toward your body and then push it forward to cut straight clean lines. Install the T-molding threshold using construction adhesive. The overlapping edges on the ends of the T-molding cover the gap.

Measure the gap

Measure the gap between the door frame and tile as you apply any of the methods discussed below, making sure you have enough tools and gears to fit the materials inside the gap properly. Measure the distance using tape.

Use a filler or caulk.

For a filler, use a wood chisel and cut the door jamb. Caulk is molded into any shape. It is durable, weather-resistant, and available in multiple colors. Caulk usually comes in tubes, and get caulk in a color that matches your door ( The process of caulking is pretty simple and requires no special skills.

Clean all the dust and sand down the surface to remove the paint. Grab the filler and make a paste to place on the surface, using a putty knife, patch up the surface smoothly and level the paste to spread evenly. Wait for 2 minutes. Wood filler is from sawdust and polyurethane, making it more durable than wood putty, although it takes longer to dry and can be more difficult to use.

To apply caulk, grab a caulk that matches the color of the door jamb. Rip the tip and make a hole around 0.25”. Squash the tube and let the cream rest on the gap which needs fixation. Use your finger to level the surface. Wait for some time.

Tape the gap

To fill the gap under your door, cut it to size using a hand saw, sliding it onto the bottom of your door. Adjust up or down to make sure you have a good seal, holding it in place by friction. No screws or nails are needed.

Measure the gap between the door and jamb and the door and stop with the door closed. Take measurements along both side jambs and the head jamb. Choose weather stripping for each side that’s big enough to fill the largest gap along its run.

Replace the door bottom

When fixing the door bottom, make sure the gap between the door casing and the floor is even on both sides. If not, your door will not close properly, or you may develop drafts around the door frame.

Use a rubber door sweep.

You can fix a gap between the bottom of the front door and the threshold with a door sweep. Door sweeps reinforce the seal between the bottom of the door and the door jamb. It offers extra protection from dirt, bugs, moisture, and wind. 

A door sweep is a plastic, rubber, or bristle barrier closing the gap between the door and the floor ( When installed on the inside surface of a door, it keeps the room airtight and prevents the entry of dirt and crawling insects. The sweeps are the screw-in aluminum door sweep and the adhesive or stick-on door sweep.

Screw on a door sweep from inside the home on an exterior door, so that the sweep will block the gap under the door. Amongst the types available is an actual bristle-type sweep that hangs below the door and blocks the door gap, and rubberized types that bulge slightly to fill the door gap.

To attach the door sweep, measure the width and transfer that measurement onto a door sweep with a marker. Protect yourself by wearing a pair of safety glasses and cutting the sweep to length with either a hacksaw or a jigsaw. 

Place the sweep at the bottom of the door and align the sweeping edge so it blocks the door gap. Mark through the pre-drilled attachment holes onto the door and insert a screwdriver bit into the drill. Screw the sweep down through the drilled holes. Check that there are no gaps between the door and the door sweep. If there are any gaps, unscrew the door sweep, and fix it. All sweeps have mounting screws for ease of application.

David D. Hughes

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