Bottom of Window Trim: Caulk or No Caulk?

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Supporting Member
Supporting Member
Jun 17, 2023
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Detroit, MI
Hello All!
I am doing painting and found that the bottoms of some window trim had water behind them when I removed the caulk. I am wondering if it is wiser to leave the bottoms open to let water out, or caulk them closed to keep water & snow from blowing in.

The sides of the trim are still sealed well, so I suspect moisture is entering at the seams in the siding shingles and wicking sideways. (Just a guess)

I'd hate to remove the brittle 125+ year old trim and wreck it. I'd also then have to have made new trim the size of the gap between the frame and the asbestos siding. That's too big a project for me.

It is very ugly with them open, so caulking is preferred- if if won't cause damage. Or, perhaps caulk with a small weep hole.

Thank You For Your Advice!

Here are some photos of the ugliness:


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It helps to find the source. Is it just pooling at the bottom because of failed caulk, or is the source from separated trim of the window, or from the caulk between the trim and the siding.

Were it I, I would temp. seal the openings where the jambs meet the sill and then, with a hose, emulate rain fall, flooding the window and
adjacent siding.
Thank You Snoonyb for your advice.
I studied all the way around each window, frame and trim and found no gaps, cracked or loose caulk. I tried your temporary seal idea and the water still arrived behind the temporary duct seal "caulk".

The only thing that I can think of is that somehow water that gets between the joints on the siding goes sideways until it gets behind the window trim, then rolls down to the sill.

Should I leave the bottoms of the trims un-caulked to let water out, or will that cause more problems by letting water, wind and insects in?
I'm not a fan of leaving weep holes in caulk, however not doing so could eventually result in the leak affecting the interior finish.

I've found that a visual inspection does not always reveal caulk that has loosened, but that physically pressuring and attempting to manipulate the caulk will.

Also, and it appears so, if both of the sashes are movable there could be window parts, such as parting beads, which are loose.

The possibility that you weather membrane, behind the siding, has failed, and the water is migrating along the studs and framing members, without it affecting the interior finish, seems remote, but can be mitigated by checking for and calking separations in the siding.
Thank You Soonyb for your excellent instructions. I really appreciate it.

Per your advice, I checked all the caulk on each window by pulling and with a dull putty knife. A whole lot that I thought was good pulled away. I primed and re-caulked with Big Stretch.

The wood parts, such as parting beads were tight and adhered, so that was one less prep step to do.

You mentioned the weather membrane. On the parts of my house that have asbestos shingles (rest is brick), it is certainly not a good seal.

From doing repairs and adding windows over the years, I found that it is tar paper and the butt joints where pieces meet are not overlapped. Also, it has many holes from nails that held the original wood siding, plus those for the asbestos shingles. (The wood was removed before somebody shingled it, but they left the old paper.) Also, at each shingle's vertical butt joint to the next shingle, there isn't a strip that is usually between shingles.

The big mistake they made was that at the bottom z-strip, instead of lapping the tap paper over the vertical leg of the strip, they tucked the paper behind the strip. All water that gets behind the shingles or in the gaps between the tiles rolls down and goes behind the z-strip. It is a real problem for the band board. Water gets in and soaks the wood.

Someday I hope to ideally brick these 3 walls to match the other three. Depending on cost, perhaps (probably) I'll side them with something that is not vinyl & looks like wood siding. Perhaps a cement composite like Hardie would suffice. (To me, vinyl or aluminum siding doesn't belong on this old Craftsman style house.)

After caulking everything, I was quite comfortable following your advice and didn't leave any weep holes. Time will tell if I still have water getting in. So I'll keep an eye on things.

Thanks Again To All!
It's good to hear that you're, "tuned in", so many just assume, until some long coming, fails.
All windioows in a modern home will have condensation which runs down the glass and onto the sill. This may be the source of your water.
All windioows in a modern home will have condensation which runs down the glass and onto the sill. This may be the source of your water.
Thanks for mentioning that. It's a good place to verify caulk integrity.

We've got old replacement sash pack windows that do exactly what you described, but only on the hottest few days when the inside air conditioner is on "Ice Rink" mode. Fortunately, on those sash packs, the old sills are tilted severely so water runs fast.
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