Why is water coming in under my sliding glass door during heavy rain?
A straight answer first, then what you can check yourself and when to have a technician look.
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In almost every case the sill is not draining. A sliding door sill is built to catch wind-driven rain and send it back outside through small weep holes at the bottom of the outer track — when those holes clog with dirt, insect nests or old caulk, water pools in the track and spills over the inside edge onto your floor.
The other common cause is a seal that has given up: flattened pile weatherstrip on the panel stiles, a loose interlock where the two panels meet, or failed caulk where the door frame meets the wall. A door that leaks in an ordinary storm is telling you something has worn out, not that the storm was unusual.
Why it happens
A sliding patio door is not a watertight wall. It is a managed drainage system — rain blows into the track, drops into the sill channel, and exits through weep holes to the outside. Anything that interrupts that path puts water where it does not belong.
Weep holes are the usual culprit because they are small and sit at ground level, where grit, leaves and pet hair collect. A few seasons of sweeping debris into the track is enough to plug them. Once the channel holds water, a strong gust pushes it over the inner lip and under the door.
The second path is through the seal rather than the sill. Sun shrinks and hardens pile weatherstrip until it no longer touches the frame, and a panel that has sagged on worn rollers stops meeting the interlock squarely, leaving a vertical gap that wind-driven rain drives straight through. Caulk and flashing around the outside of the frame age the same way.
This matters beyond the wet floor. Water that gets under a sill soaks the subfloor and the framing where nobody can see it, and that damage builds quietly over several storms.
What you can check yourself
Find the weep holes
Look along the bottom of the outer track, on the exterior face of the sill, for small slots or holes. If you cannot see daylight or they are packed with grit, that is likely your answer.
Clear the track and the holes
Vacuum the track out, then clear each weep hole gently with a soft brush or a pipe cleaner. Pour a cup of water into the track and watch whether it drains outside within a few seconds.
Check the weatherstrip by eye
Slide the door closed and look along the stiles and where the two panels overlap. Pile that is matted flat, missing in patches or no longer touching the frame will not stop wind-driven rain.
Look at the outside caulk
Walk outside and check the joint where the door frame meets the wall and the threshold. Cracked, shrunken or missing sealant is a direct route for water.
Note where the water appears
Water at one end of the sill points to a drainage or slope problem; water along the whole bottom edge points to the seal. Telling the technician which it is saves diagnostic time.
When to call a pro
If the weep holes are clear and water still comes in, the leak is in the seal, the interlock, the panel alignment or the flashing behind the frame — none of which is a homeowner fix. The same is true if the floor, baseboard or drywall near the door is swollen, stained or soft, since the water has already been getting in for a while.
Stop using the door and call if the glass is cracked or a panel has come off its track. A sliding glass panel weighs about as much as a person and breaks into the room, so that work belongs to a technician. One Call Sliding Door Repair arranges the visit with an independent local technician anywhere in the fifty states; the estimate is free and the technician confirms the price with you before any work starts. Licensing rules for this work are the technician's own and vary — your local building department or state licensing agency can confirm what applies where you live.
Free tools for this
- Draft and leak locatorWhere is the air or water getting in?Open →
- Seasonal prep checklistWhat should I do to my sliding door each season?Open →
What the technician will do
- Clear and test the sillThe sill and weep holes are cleaned out and flushed so the channel drains the way it was designed to.
- Replace the pile weatherstripWorn pile on the stiles and at the interlock is replaced so the panel seals evenly along its full height.
- Check alignment and the interlockThe panel is adjusted so it closes square and the two panels meet tightly, closing the vertical gap that wind-driven rain uses.
- Inspect caulking and flashingThe sealant and flashing where the frame meets the wall are checked and resealed where they have failed.
- Rain and wind test the resultThe seal is tested with water before the technician leaves, so you know the fix held rather than waiting for the next storm.
Related questions
- Can I just put a towel or a rubber seal along the bottom?
- A towel manages the symptom for one storm and a stick-on seal can actually trap water in the track. If the sill cannot drain, blocking the inside edge pushes water further into the floor structure instead of out.
- Why does it only leak when the wind blows from one direction?
- Wind pressure on one face of the house drives rain into the track faster than it can drain and pushes it through any gap in the seal. That pattern usually points to clogged weeps combined with tired weatherstrip on that side.
- Does a leaking door mean the whole door needs replacing?
- Usually not. Most leaks come down to drainage, weatherstrip, panel alignment or exterior sealant, all of which are repairs. The technician can show you the worn part and put the reasoning in writing before anything is done.
- How do I get someone out to look at it?
- Call (888) 851-3682 or send a request through the form on the website, and One Call Sliding Door Repair will arrange a visit with an independent local technician. The estimate is free and you approve the price before work begins.
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