How do you fix a gap on the bottom of a door?

What causes gaps under doors?

There are a few common causes for gaps appearing under doors:

• Warped or sagging doors – Over time, doors can warp or sag, creating an uneven surface and causing gaps under the door. This is especially common with solid wood doors.
• Improper installation – If a door is not properly installed in the frame, it may not sit completely flush, leaving gaps. Issues like unlevel thresholds or improper shimming during installation can cause this.
• Settling of house – As a house settles over time, it can shift doors out of alignment, creating gaps under them. This usually happens slowly over many years.
• Worn out weather stripping – Weather stripping on the bottom of the door degrades over time. As it wears out, it may stop forming a tight seal, allowing gaps to form.
• Moisture damage – Exposure to moisture can cause wood doors and frames to swell, twist, and warp, resulting in gaps under the door. Preventing water damage is key.

So in summary, the four main causes are warped/sagging doors, improper installation, settling of the house over time, and worn out weather stripping. Diagnosing the specific cause will help determine the best solution.

How can you fix gaps under doors?

Here are some of the most common and effective ways to fix gaps that appear underneath doors:

Adjust door hinges

If the door is sagging, you may be able to raise it back into proper alignment by tightening the screws on the door hinges. This can eliminate gaps caused by a warped or sagging door. Just take care not to overtighten the hinge screws or they could strip out of the frame.

Add weatherstripping

Replacing worn out weatherstripping at the bottom of the door and on the frame is an easy fix for gaps caused by degraded seals. Use a thick rubber or vinyl sweep weatherstrip for the door bottom. Make sure the new weatherstripping makes continuous contact with the threshold when the door is closed.

Trim door bottom

For minor gaps under 1/4 inch, you can simply plane or trim the bottom edge of the door using a wood plane or rasp. Remove just enough material to eliminate the gap. This is only a good solution for solid wood doors.

Add door shims

If the gap is caused by improper installation or settling, adding shims under the door hinges can raise it back into proper position. Loosen the hinge screws, tap in wooden shims to raise that corner, then retighten the hinges. Go slowly and recheck for level frequently.

Fill gap with sealant

For very small gaps under 1/8 inch that do not close fully with weatherstripping, you can fill them with clear silicone caulk. After cleaning the gap, run a thin bead of caulk and tool it smooth. Once dry, paint over if needed. This is only an aesthetic fix for small gaps.

Adjust bottom threshold

If the threshold is not level or is poorly fitted, gaps may persist under the center of the door. Carefully chisel or plane down any high spots on the threshold until it sits perfectly level. A threshold adjustment may be needed with new door installation.

When to call a professional

While many minor door gap issues can be addressed with DIY methods, there are some situations where you may need to call in a professional:

• Door is badly warped or damaged – Significant warping often requires door replacement.
• House framing issues – If the door frame itself is out of square, a carpenter may need to make structural adjustments.
• Improper original install – Only a complete redo of the original installation can fix fundamental flaws.
• Moisture damage – If swelling indicates deeper water issues, you likely need professional repairs.
• Skill exceeds DIY comfort level – Some repairs like planing doors and adjusting thresholds take skill.

So if the issue is beyond your abilities or indicates larger problems, don’t hesitate to call a professional. A carpenter can assess the situation and determine the right solution, whether it’s adjustment, repair, or full replacement.

Preventing gaps from recurring

Once you fix a gap under a door, you’ll want to take steps to prevent it from recurring. Here are some prevention tips:

• Seal wood doors – Apply polyurethane or varnish to protect from moisture and prevent warping.
• Improve weatherization – Ensure weatherstripping makes full contact and insulation is adequate.
• Maintain hinge screws – Periodically tighten hinge screws to account for loosened joints over time.
• Check alignment annually – Do a quick visual inspection for gaps developing each year.
• Keep stable humidity levels – Large humidity swings can make wood doors swell and shrink.
• Level sloped floors – A sloping floor will cause the door to settle and warp.

Routine inspection and maintenance are key to preventing recurring gaps. Also address any moisture issues quickly before major swelling and warpage occur. With diligent prevention, you can avoid having to repeatedly fix gaps under doors.

Steps for fixing a gap under a door

Here is a simple step-by-step process for diagnosing and fixing a gap under a door:

1. Inspect the door and determine the cause – Check for warping, sloping, swelling, worn weatherstripping, etc.
2. Try tightening door hinges first to realign – Often a quick fix for minor sagging.
3. Install new weatherstripping if worn out – Ensure full contact between sweep and threshold.
4. Make minor door bottom adjustments – Plane or trim door edge if gap is very thin.
5. Add shims if door needs raising – Shim under hinge side to lift door.
6. Fill very small gaps with caulk as needed – Tool caulk smooth and paint to match.
7. Consider professional help for major issues – Replacement or framing fixes may be needed.
8. Seal and maintain door to prevent recurrence – Varnish wood, tighten hinges, and inspect annually.

Following these steps in order can help identify the ideal fix. Start with easier solutions like weatherstripping and shimming first before attempting structural changes. And remember to seal and maintain the door afterwards.

Conclusion

Fixing annoying gaps that appear under doors can improve energy efficiency, security, and appearance. In most cases gaps can be fixed with common DIY methods like adjusting hinges, replacing weatherstripping, planing the door edge, adding shims, and using caulk. For recurring gaps or more complex issues, professional repairs may be required. But with routine maintenance and sealing, most gaps under doors can be prevented from returning.