I have a sliding door with glass panels on each side, spanning a width of 12 feet. The door has been sagging in the middle. It slides easily at the edge (when open), but drags near the center. I tore off the siding and flashing above the frame outside and found 2 1-inch wide shims between the header and the door frame right in the center of the door (shims lying on top of each other filling the approximate 1/4 inch gap)

It looks like the pinch in the slide is exactly at this point. To my eyes, it seems that the header is putting its weight on those shims, pushing down on the frame.

A few questions:

  1. Can I remove those shims? I cannot imagine that the 12' header was suppose to be supported by either the shims or the frame, so I think that I can do so safely.

  2. Those shims are pinched pretty good... how do I remove them? I could reach a saw blade in and just chip them out I suppose...

  3. Should I be worried about the sag? The house is 32 years old and with those shims any sag would be immediately felt by the door frame, so I can confirm the sag isn't that much since the door can still open and close.

Thanks very much for any help! This is outside my normal DIY home repairs and experience, so any advice would be appreciated!

  • Photos would be worth a million here. I'm having trouble imagining what a 12 foot wide patio door even looks like.
    – isherwood
    Commented Nov 2, 2020 at 22:22
  • 1
    Are you saying that there are two stationary panels and two sliding panels?
    – isherwood
    Commented Nov 2, 2020 at 22:28

2 Answers 2


Without a full mental picture, here are my initial suggestions...

Can I remove those shims?
Probably. Head jamb anchor points are sometimes needed to prevent horizontal (in-out) movement in the frame, but if you have mounting flanges or something else on the door to do that they aren't needed. Most doors I've installed have been done without head jamb shims for just this reason.

How do I remove them?
A reciprocating saw (Sawzall) will cut the nails or screws and leave a bit more space to remove them. A flatbar as a lever can also relieve pressure.

Should I be worried about the sag?
You haven't told us what the header is, nor how much sag you're seeing. Chances are it has sagged all it's going to sag, unless the header was drastically undersized. Do you see evidence of sag above the header? If that's substantial and growing you should get an expert on site.


You have an XY Problem.

I firmly believe the problem is not that the shim are there but that the header is sagging under the load of the building above. If there is a floor above this doorway, put a marble on the floor and see if it rolls toward the spot where the shims are. If it does, this guarantees that you've got a sagging floor/header. If there is no 2nd floor above, it'll be harder to prove, but holding a level across the top of the door and across the bottom of the header will show where any lack of straightness is. You may need a 6' or longer level to test this out. (There is a store that goes to the Harbor for its Freight that sells 6' levels for all of about $20, other stores sell 'em for $80 or more - your call.)

The shims are there because door and window openings are always roughed in bigger than the item designed to go in them. This allows the door to be installed nice and square so it operates properly, then the shims are installed and the door frame is nailed/screwed through the shims to hold it in place.

Removing the shims will allow you operate your door for a while longer. Then the header will sag enough that it's directly pinching the door frame. When that happens, you won't have any more shims to remove to use as another band-aid to temporarily fix the problem, so you'll have to address the actual issue then. Better, IMHO, to do it now before it impacts other things.

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