Background: 20 year old house with original Bilco classic bulkhead door (see image below). Water was leaking in around the metal Sill and rotted the top step and stringer. I removed all the old caulk around the perimeter which was in bad shape and replaced it with a heavy hand of Sika Polyurethane Construction Sealant per the Bilco caulking instructions. Additionally, I purchased and installed the Bilco weather stripping kit for additional protection.

Bulkhead after caulking perimeter and Bilco weather stripping kit Bulkhead after caulking perimeter and Bilco weather stripping kit

Problem We got some rain recently and water is still penetrating what appears to be under the recently caulked sill (see pictures below). Am I missing something? Is it saturating the concrete and getting under the Sill?

Top view of Sill leakage Top view of Sill leakage

enter image description here Close up of Sill from outside

enter image description here Closeup of Inside Sill with bulkhead doors closed

4 Answers 4


They leak

All the wood on the stairs should be pressure treated, since they always leak, in my experience. They are a standard product "everybody uses" that is not that good at what it does.

If you really want to tilt at windmills, dismount, seal, and remount, but "dismount" is likely to be a frustrating battle with rusted fasteners...

Actually, if you get the seal perfect, you'll still have condensation forming on the inside and running down the doors to that point (maybe you even got it perfectly sealed already...) If there isn't an airtight insulated door at the bottom of them, that's standard practice, since warm moist inside air hitting the cold steel will make vast amounts of water (inside), so you want to limit inside air contact when you are not actually passing through the doors.

You might also want to paint/seal the concrete in the stairwell to limit the moisture coming off that into the closed air space. Doing the same to the exterior concrete would aid water running off, rather than wicking through, without the hassle of the arguably better (but definitely a lot more work) approach of making sure all that concrete slopes away from the base of the doors, which should have been done, but appears not to have been done.

  • I'm definitely going to rebuild with PT and joist tape on the stringers for that matter. When I was removing caulk I noticed the installers had not put any caulk on the sill only the sides. It appears because of this the caulking surface was less than smooth. I've been toying with the idea of removing the sill, resurfacing with a resurfacing concrete and then reinstalling and caulking. Thoughts?
    – Nate
    Commented Nov 12, 2022 at 15:18
  • It will be a lot of work, but if you want to do that, it should work. Do pay attention to drainage slope beyond the edge of the door footprint. Another approach would be to grind it smooth and put the drainage slope in that way as well. Hot tip if building new stairs - make them easily removable for when you need to hoist rather than slide-down-stairs something really heavy into (or out of) the basement.
    – Ecnerwal
    Commented Nov 12, 2022 at 15:36
  • That's a good point. The builder did everything with nails so removing the top tread was an absolute nightmare. My concern with grinding it smooth is that the sill height wont line up with the bolts on the left and right side anymore. I figured just unbolting the sill and using resurfacing concrete would allow me to maintain that.
    – Nate
    Commented Nov 12, 2022 at 15:42

Appreciate all the advice given to me. After weeks of trial and error and different test cases it turned out that the caulk job on the sill was not sufficient. There were two areas where the concrete had worn away and the caulk wasn't pushed into the crevices. I cleaned the caulk per the manufacturer and put another layer deep along the concrete and the issue is resolved.

  • Do the Bilco caulking instructions call for backing rod in any location on the door?
    – mr blint
    Commented Nov 30, 2022 at 20:04
  • 1
    Not that I had seen and I looked at the most recent manuals and the one for my specific door from ~03.
    – Nate
    Commented Nov 30, 2022 at 20:06

Just a few additional points that might be worth looking at:

  1. Sometimes the bulkhead enclosure, rather than the door, is the source of the leak. (In my case, one source of leakage was a dubious seal between the cinder-block stair enclosure and the cast-concrete foundation.)

  2. In an older door, look for places where a previous owner might have modified it. A past owner had fitted mine with slide-bolts, thinking they would improve security. They don't, but the holes cut for them in the frame are a water leak point. Attempts to close this damage with epoxy and such have been minimally successful; I expect I'll have to just replace the doors at some point.


When rain hits, it bounces/splatters.

The design of this door relies on rain going downward only. But there's a flat surface of stone-in-concrete right in front of the front door lip. The rain is hitting that, and bouncing/splattering upward, thus slipping under the door lip, which is totally not designed to exclude rain going upward.

Check the installation instructions but I bet they suggest not having a flat surface right in front of the front door lip.

  • That makes sense because I had a hard time believing that, that much water was getting through the newly caulked sill. The leaky right side door has some gaps even with the weather stripping that the non-leaky left does not. I might try and add some additional weather stripping to prove this is the cause.
    – Nate
    Commented Nov 13, 2022 at 13:25

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