The photos above were with the sliding glass door closed, and just the screen door slid open. This photo is looking down on the threshold with the sliding glass door open, if that helps.

Any idea as to a model number or glass ID? Usually you can pull up a model cross section and see where the issue might lie and where the fix might be.

All I know is that it's a Pella Proline wood-clad sliding glass door. Thanks.

I found the number on the glass. It was really hard to read.

16CFR 1201 II SGCC-1829 3/16U

As I mentioned, it's a Pella Proline (or at least, that is what I was told were the windows when I bought the house).

Thank you for your help.

If this section is reflective of the door in question, i.e. if its the same design, then it appears the aluminum sill section is a sloped design and steps up into the interior wood threshold. I would go ahead and apply some sealant in the corners where that aluminum sill meets the jamb wood (be sure to not obstruct the drainage path) and possibly some between the aluminum and the threshold but I doubt that is where it is coming from.

Cross section

Thanks Windows on Washington. Does your comment "but I doubt that is where it is coming from" mean that your recommendation will likely not work? Are you saying the water coming into the ground floor entry door is not entering via the threshold? I am sorry, but I didn't understand whether you are advising something else in addition to those instructions of applying sealant.

I would follow WOW's suggestions to see if this can be remedied with a simple fix. This is where he is going: If that doesn't work, the door should be removed and a sill pan installed under the existing door and of course new flashing and re-installed. A lot of work and expense. You seem satisfied overall with the door but Proline is a medium quality at best door. You might also think about replacing the door at the same time. WOW - what is the PG or DP for this door? I think it is only a 20 or 25 so the door may be getting overwhelmed by your conditions.

Thanks very much!

In response to your points:

- One reason we concluded the threshold was the problem, is that I took a Pyrex glass measuring cup of water, and carefully poured water just onto the threshold to see what would happen. The water came in through the top frame of the ground-floor entry door directly below as if being poured through a sieve.

- Just some background: I have lived in this house for several years, and this has not happened before. It is a new problem. So if the sliding glass door is being overwhelmed by my conditions, wouldn't it have shown before now? I had been assuming it's just wear and tear of the threshold - you can see how the threshold looks in the pic. But I am wondering if I will need to replace the whole unit or not.

P.S. I am outside of Chicago, so conditions are not the easiest. But this door is rarely used - a Juliet balcony is always kinda useless, but it came with the house.

You can't just service the threshold. If you tear it out, replace the door as it is not worth fixing at that point.

Try caulking the locations that I said first.

Thanks WOW. Is there a particular caulk that I should use?

Silicone is good if you aren't needing to paint it. Its what we put frameless show enclosures together with.