Mitered joints in casings opening up - what to do?

Recaulk, and get a humidifier.

Take the trim off and rebuild the door opening making it smaller at the bottom. When you reapply the trim the joints will close. You will also have to trim the door at an angle.
If that's too much work, then just caulk it and repaint.

Take the trim off and rebuild the door opening making it smaller at the bottom. When you reapply the trim the joints will close. You will also have to trim the door at an angle.
If that s too much work, then just caulk it and repaint.

- jbay

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This seems like a great idea!

Will the caulking be flexible enough to expand and contract with the seasonal movements? Or will get squeezed out when the summer comes?

Call it character

Do you use o humidifier to maintain moisture levels in the house during winter? This will help the house and the people in it, as well as make a given temp feel warmer. You can get a % RH / temp meter cheaply at the bbs. I try to maintain mine at 40% min, its usually in the mid 40's. Keeps moisture in all the wood maintainings door and window weather seals. Its not just the trim moving but also what it is attached to. I've had good luck with flexible non shrinking paintable sealant in an app like yours.

A number of things could be causing it (casing movement, door frame movement, etc.).

What I do is spline the miters so there is no way they can separate. After this, it just comes down to a mounting method that allows for movement.

Typically I'll avoid any fasteners between the casing assembly and door frame that are within 6" of the miters. This allows the casing to bend a tad without breaking the miter.

My splines are really a form of lap joint. I cut away about 1/4" from the rear of each piece and then glue in a 'spline' that laps into the cuts. The spline grain direction is perpendicular to the miter for maximum strength.

One could just do a half lap with the two trim pieces, but I found that doing the spline on the back to be easiest since the front of the trim is rarely flat 8^)

Your glue/pocket screws method should be fairly ridged, perhaps just keep the nails about 6" away from the miter and see if that cures it?

No, we don't currently run a humidifier. It's a good point and something we should probably do for comfort purposes.

At some point, I had the idea of using my biscuit jointer to reinforce the mitered joint. But due to the profile, there isn't enough wood in the center of the casing. This led me to pocket hole screws, on the edges of the casings. Another option I considered was bowties (or dutchman), though wasn't knowledgable enough to know how to pull that one off.

Leaving some space for flexing and wood movement is a good idea. I'll be sure to do this in the next ones I do.

When I was putting in trim in a condo, where nothing was square, vertical, or horizontal, the painter showed me his tube of painter's caulk and told me not to worry about it.

Please don't use caulking. It will shrink, discolor and look awful in a few months.

Not real thrilled with fillers either.

I would run a saw blade to even out the crack and then inject epoxy and put a nail through miter from top to draw together. Wipe off squeeze out immediately any gaps will be filled with epoxy.

You could also clamp from side to side there will be enough flex to draw it together the diff in reveal won't be that noticeable.