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Community and Q&A

exterior door threshold slopes towards door

Trevor_Lambert | Posted in General Questions on

I’ve recently discovered that the threshold on the door leading to my “flat” roof balcony is not only not properly sloped, if anything it actually slopes toward the door. The door threshold is really deep, about 18″, so this makes the problem even worse. I’ve been trying to figure out what to do about it, and at a loss. Do I have any options besides removing the door, tearing up the deck membrane and doing it all over again? The builder is long gone and of no help.

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  1. Expert Member
    Michael Maines | | #1

    Trevor, unfortunately, door sills/thresholds are already vulnerable parts of the building envelope; if yours is sloping in the wrong direction I don't know of a solution other than taking it out and starting over. A skilled carpenter can remove the threshold without removing the entire door, but unless you have very high-value finishes, it's probably easiest to bite the bullet and pull the door.

    It's not uncommon on balconies to need to raise the door up on a plinth in order to flash it properly; the building code is a little murky when it comes to required details on this, but I believe it's ok to have the sill up to 7 3/4" above the floor on either side. A photo of your situation would help a lot.

  2. Trevor_Lambert | | #2

    I will take a photo when I get home tonight. The deck is well below the door threshold, so there's no reason to have not done it (he said he was going to, must have had a broken level).

  3. Trevor_Lambert | | #3

    Here are a couple of photos.

  4. Expert Member
    Michael Maines | | #4

    Trevor, those photos help a lot. It's not really what I was picturing. If your goal was to create a water collection device, I'd say your contractor did a pretty good job. The area outside the door is likely raised because it's the interior floor system carrying through, and the deck surface was framed a couple of inches lower.

    If door frames were totally waterproof, maybe you could bring a new slope up to the front of the door sill, but it's much safer to have a pan that extends under the door with a backdam on the interior. Especially when there is little to no step-down on the exterior side of the door.

    That leaves your options as:
    1. Remove the door, create a new slope outside the door and a pan extending under the door, or
    2. Remove the membrane and re-frame the area outside the door with a slope toward the rest of the deck. I'm not familiar with the roofing membrane used; EPDM is still standard in my area, but it looks like it's weldable. Depending on your floor framing system, there is a chance you could remove some material to create a slope, but you should have an engineer look at it if you choose this route.

  5. Trevor_Lambert | | #5

    That area outside the door is not part of the interior floor system. It was all done very quickly while the decking guy was waiting to do his job, so I only have a fuzzy memory of what it looked like, but it had to be just a piece of exterior plywood set down as they were finishing the deck roof and installing the door. Can you link me to any pictures of what a pan with a back dam looks like? Option 2 seems like the easiest option. It's vinyl, and heat weldable. It would mean the membrane would just butt up to the door frame rather than go under it. Is that ok, as long as it's sloped correctly?

  6. Expert Member
    Michael Maines | | #6

    Trevor, it's interesting that it's not part of the floor system. What were the exterior walls built on? Assuming you know your own house better than I do, I'd suggest reading: (a piece I wrote long ago; in the meantime flexible pans are now the norm)

    Several wise contractors have told me "doors always leak." Even high-performance, triple-glazed european doors are not immune. I'm embarrassed to say that the Thermatru entry door I installed on my own, antique house leaks when the rain hits it just right (a larger roof overhang would help, but not against the driving rain we sometimes get). Others say that their doors don't leak. It's always safer to include a sill pan, but if you're feeling lucky, and especially if you're in an area that's not windy and rainy and you have a roof overhang, you might be fine without one.

  7. Expert Member
    Michael Maines | | #7

    Got it, thanks for the explanation. I'm sorry this happened; good builders can be hard to find.

  8. Trevor_Lambert | | #8

    The house is made of pre-fabricated wall panels. The second level walls rest directly on the lower level walls, and the floor is entirely within that footprint, attached with joist hangers onto an LSL header.

    I realise I need to remove the door and get a sill pan under there. Just another in a long list of grievances I will never get to file with the builder.

    I'm also realising this isn't going to be a straightforward fix. The width and extra depth of the door frame probably means I'm making the pan myself.

  9. Trevor_Lambert | | #9

    So I'm dredging up this topic for more advice based on more accurate information.

    I did what I thought was a temporary fix, basically just sealing the joints as best I could, monitoring and touching up if necessary.

    Now that I'm looking at it again, the threshold doesn't actually slope toward the house. The reason the water was pooling by the door is a combination of two things. One is that the slope, while actually going away from the door is very slight, about 1/8" in a foot. Second is that when the membrane was installed, they didn't have enough material to cover the threshold all in one piece, so there is a seam where the membrane overlaps with the next course. This overlap negates the slope; it averages out to level, but because of the abruptness of the change at the seam, it's been acting like a shallow pool.

    I'm going to replace the membrane covering the threshold, and move the seam to beyond the edge of the threshold, where there is a vertical drop of about an inch. This will restore the effective 1/8" per foot slope. So my question is, should I take this opportunity to increase the slope to 1/4" per foot, or is 1/8" good enough? I want to do what's required, but it's a lot more work to try to add the extra slope so I will only do it if I feel I have to.

    1. Expert Member
      Peter Engle | | #10

      Trevor, I can see in the photos that there are humps/wrinkles in the membrane, and I think I see the seam overlapping as well. You're right - that can certainly negate the function of that little slope. If you are going to pull the door to fix the membrane - and you should so that you can run the membrane up into and becoming the sill pan - that would be an ideal opportunity to increase the slope a bit. Depending on how it was framed, you may be able to run the slope down to meet flush at the deck without too much effort. That would be the best solution. With areas like this, more slope is always better. But if it looks like a giant PIA, 1/8" per foot can work, in ideal conditions....

  10. Expert Member
    MALCOLM TAYLOR | | #11


    I hate to say it, because it involves an awful lot of work, but that door needs to be a couple of inches higher. I think the problem came from the original decision to treat the threshold as a sill-pan. The much safer detail is to have a curb the door sits on separated from the sloped part in front. Having the sloped membrane extend under the door is asking for trouble.

    If the main deck membrane slopes away from the door, the small sloped area could be eliminated. That would leave you the desired curb at the door without lifting it.

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