Outdoor joinery question

[billmeyer]

Robinson,

I like your idea of a sweep. I have had many storm windows with weep holes, and always thought that the holes let in cold air, which the storm windows are supposed to keep out. Your solution would fix that.

Bill

[charlese]

It can suck up into the end grain of the side rails like a straw which is exactly how the tree moved its sap. Trees don't really have hearts pumping that stuff you know.

You are right on Francis! Here's a short note to speak for the trees:

Yeah, Trees don't have hearts to pump the water up, but they do have leaves or needles that when respiring, are pretty efficient pumps in themselves. Trees must pump the sap up in order for it to reach 100 or more feet high. Capillary action just won't do the job alone.

Capillary action can cause bad things to the stiles of storm windows, but capillary action is limited to a couple inches or so.

[TFF]

This would be my vote.
On another note: I would make the storm window a tiny bit shorter (maybe 1/4") than the opening and use something like a vinyl sweep at the bottom to seal it. Even when the sill slopes well it always seems like water collects between the sill and the storm window (usually from condensation or frost) and soaks into both of them. Many old storm windows were built with vents to let that moisture out but it still collects at the bottom. Several windows I have that need some repair now are from that. If they are too tight the water will be held in that bottom space by capillary action. On the sides gravity will drain it out but on the bottom the gentle slope will not prevent the capillary action from retaining the water. It can suck up into the end grain of the side rails like a straw which is exactly how the tree moved its sap. Trees don't really have hearts pumping that stuff you know.
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On gluing exterior joints I have noticed that Tommy on This Old House now often uses regular caulk in mechanical wood joints. Seems logical...

Francis, I think you hit the nail on the head with the capillary description. I hadn't considered that. The current configuration has two slots (1/4" saw kerf cuts) spaced 1/3 in from each side through the base to weep. They also have a 15 degree bevel on base bottom (short side of base facing inward). I suspect this was meant to curb the capillary action. I wonder if I could rip a membrane material that I tack to the beveled bottom edge (full length of base bottom). This would not be viewable from exterior or interior and might stop the capillary action.
TFF

[TFF]

iClark, Thanks for the suggestions. I had tried the PVC product -nominal 1 1/16" depth, same as the wood. The problem is flex. When you rip down to 1 1/2' w, there is way too much flex in the stiles versus wood. I had to scrap the whole machined run of 12 windows on the chance that wind conditions could bow the sides and result in a free falling glass storm window. Not a good outcome. Machining PVC plastic material creates nasty air. I had to wear a dual stage filter mask the whole time and that was with my 3 stage ceiling filter and my high volume dust collector running. The particles are fine and become magnetic from static.
TFF

[iclark]

TFF,

thanks for the feedback.

as luck would have it, I've only cut the PVC with machines sitting out on driveways or sitting in the grass. I noticed the static cling but I was sloppy about the respirator. the fine particles never even occurred to me (and I am definitely trained to know better:o ). thanks for pointing out what should have been obvious to me.

as for the flex issues, you are absolutely correct. I had not considered the small cross-section size in terms of flexure. I wonder if there is a good PVC to plexiglass glue. the thermal expansion coefficient might be close enough between the 2 plastics (might not, though, I don't have tables here) that one could glue-up a sealed, double-pane storm window that would be stiff enough and also have the double-pane insulation advantages.