Replies

1. 
   andyfrog | May 31, 2023 01:30am | #1

   He says it's a wick, so wouldn't it also transport incidental moisture upwards?

2. 
   user-1116814560 | May 31, 2023 02:47pm | #2

   With gravity working in your favor, probably not a concern. I’ve heard landus actually spayed a hose directly onto the wicking and did not have aN issue with water getting up and into the window even when saturated .

3. 
   Malcolm_Taylor | May 31, 2023 04:16pm | #3

   I'm sure it works well, I'm just not convinced it's necessary. Sill-pans are much like rain-screens: If you have enough water accumulating on the pan, or in a wall, that it needs to actually drain, as opposed to dissipate or diffuse, something has gone very wrong.

   The damage I've seen to the framing around the window R.O. has always been from prolonged wetting, without enough capacity to dry. Even in cases where the framing and sheathing were completely rotten, there was never enough water at one time to drain.

   What I think is important is the presence of an impermeable membrane to protect the lower jamb and sill, and a drying path for any moisture that gets in there. That's a simple as slightly gaping the un-caulked flange at the sill. I'm also unconvinced that any bulk water that gets into the rain-screen cavity could move upwards onto the sill behind the flange. If it can then we need a similar product for every other detail that relies on lapped joints, like head-flashing, etc.

1. Expert Member
   Michael Maines | May 31, 2023 04:30pm | #4

   Malcolm, it's the "slightly gapping the un-caulked flange at the sill" that this product is made for. While I have carefully inserted shingle tips and bamboo skewers to space the bottom flange off the wall enough to drain if necessary, it's finicky work and a detail I rarely see builders doing. When the windows are large and the lower flange is supposed to be fully nailed, providing a gap can be tricky. There's also the issue of maintaining airtightness; while I transition the air control layer to the window interior, and leave the area under the sill uninsulated, most builders are still foaming all sides of the window. The wicking material helps on all of these fronts. But if you are a knowledgeable, conscientious builder, you probably don't need to use it.

1. 
   Malcolm_Taylor | May 31, 2023 05:00pm | #6

   Micheal,

   If you are slightly gapping the window to provide a space at the sill-flange, you need to slightly gap the head and jambs too or the window will not be sitting plumb in the opening and all your interior trim would need to be different widths. If you are using some material to slightly gap these other areas, is there any real advantage to using the wicking material at the sill, or just use the same stuff there intermittently?

   One way to create the gap is to mount the windows outboard of the rain-screen strapping. The other, which I do, and avoids having to fur any of the window out is to set my circular saw about 3/16" depth and hog out two gaps in the sheathing at the sill. The sill-pan membrane gets pushed back into them creating a drainage path for moist air to escape into the cavity.

   While I do that, and slope my sills, I'm fairly sure the vast majority of the improvement in the durability of that area comes from adding the membrane as a sill-pan. If we had just added that detail, and never done any of the other things we do now, I think we would have achieved much the same results.

1. Expert Member
   Michael Maines | Jun 01, 2023 08:38am | #8

   My walls are usually thick and often have drywall returns, so interior extension jambs are custom-made anyway, but I agree that avoiding tapers is best. Your idea of sawing out channels is smart; like I said, conscientious builders have lots of options. I see the wicking material as something I could spec for the builders I avoid working with, or that a builder can give to a relatively inexperienced carpenter and get an acceptable result.

4. 
   user-1116814560 | May 31, 2023 04:52pm | #5

   Malcolm there is an inherent tension between ‘impermeable ‘ and ‘drying path’..this is reflected by fact most American window manufacturers push to leave the bottom open, whereas most euro window manufacturers seal tightly around entire window. However, the euro windows are typically innies more or less, and they like a vapor permeable tape - you pretty much have to go to euro tape manufacturers though hUber now has (finally) a somewhat permeable tape (3 perms) I also get confused when architects and builders obsess over air sealing three sides of a window and then just (excuse the pun) blow off the bottom side- i I also don’t like vapor impermeable walls taped with vapor impermeable tapes. I can’t say it’s a critical concern, but Vapor permeability is always a desideratum , let’s not kid ourselves, when you can use a vapor permeable sheathing, insulation WRB, tape, on wallls, use it-its better; I can accept the compromise but not the excuses. Michael points out rightly the ease of application, I think this helps close the air gap so to speak , retards water penetration , and facilitates water evacuation ESPECIALLY sill is not sloped. Sticking this tape on beats cutting your cripples with 5 degree slope, cutting a cedar shingle or using shims. Now that’s a really good compromise. And arguably superior to a strictly barrier approach. And I think we all have to admit all windows leak eventually.

1. 
   Malcolm_Taylor | May 31, 2023 05:10pm | #7

   deuceadvantage,

   I agree. The only place it makes sense to use impermeable materials is as a sill-pan where some moisture may accumulate. My only point was that while there needs to be a drying path, I don't think it doesn't needs to be a drainage plane, so I'm not sure another specialized material is necessary when there are alternatives.

5. 
   user-1116814560 | Jun 06, 2023 02:45pm | #9

   There are several factors to why my Wic-Dri will not wick moisture up (capillary action) into the window opening even thou it wicks water out and down. Wic-Dri was specifically designed for wicking moisture and is made from a matrix of spunbonded impermeable synthetic microfibers that are nonporous that resist moisture absorption, therefore helping prevent a capillary action. Capillary action can be controlled and limited by a nonpermeable material, because it needs adhesion, cohesion and surface tension like paper toweling to draw moisture upward. Plus, capillary action will not overcome gravity pull which is a stronger force in this scenario.

   I could go on, put this pretty much explains why moisture will not wick back up into the window opening. You will also notice that my installation instructions say to apply Wic-Dri 1/2" down from the sill, so once water starts pouring over the sill edge, gravity goes into action. I hope this answers the question.

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