Replies

1. GBA Editor
   Martin Holladay | Sep 21, 2012 04:16pm | #1

   Roy,
   As you probably know, Enviro-Dri is a liquid-applied WRB. In case you didn't see them, here are two relevant articles. First, a review of Enviro-Dri; second, an article on liquid-applied WRBs.

   The problem encountered by another GBA reader in a house with Enviro-Dri was unrelated to the Enviro-Dri.

   I haven't heard any negative reports about Enviro-Dri. However, if you are nervous about using a product that is relatively new, you can certainly stick with a tried-and-true WRB like asphalt felt. There are other ways to reduce air leakage in walls than by using a liquid-applied WRB.

2. Expert Member
   Dana Dorsett | Sep 21, 2012 04:47pm | #2

   The spec says its vapor permeance is ~12 perms, which is plenty of drying capacity, comparable to Typar, but not as permeable as most Tyvek products.

   Mold in a basement has nothing at all to do with the housewrap & WRB unless for some reason it's mis-installed and leaking. In general it's a lot easier to screw up the lapping of sheet goods than it is to miss spots and leave gaps in spray-on stuff. But it's the lapping of the window & door flashing at the WRB that's most critical to get right.

   In the temperate rainy Kitsap Peninsula putting a "rainscreen" gap of at least 1/4" (3/4" is even better) between the siding and housewrap is good insurance against moisture buildup even wiht imperfect housewrap/WRB. Even when the windblown rain penetrates the siding it has room to drain and dry quickly. (10mm or about ~3/8" of rainscreen is required by code in Canada.)

   Bigger roof overhangs (18-24") also limits the amount of rain penetration too, especially on single-story construction.

   Building into a slope always has some drainage issues, be sure that's treated well both at the footing and in the waterproofing. Going with insulated concrete forms (ICF) for the sub-grade part of the wall is more expensive than insulating only from the inside, but can be a cost savings from a scheduling point of view. It's worth putting an inch (~R5) of XPS or EPS under the slab too, fatter at the exterior edges, which keeps the slab warm enough to not worry about mold growing under rugs or other susceptible finish flooring.

   For the above-grade walls I'm a big fan of 2x4" framing + 2" of rigid foam (any type) in that climate, which may affect your choice of WRB. With unfaced batts or blown cellulose and 2" of EPS you end up with an R19 whole wall (with the thermal bridging of a 25% framing fraction factored in), and it's the same thickness as a 2x6 wall that comes in at only R13 after thermal bridging, making detailing around windows fairly straightforward. If you go with polyiso instead of EPS you'd be somewhere around R22 whole-wall, and it's a bit easier to air-seal the foil-facers with FSK tape than it is to tape/foam seal EPS. If you go with an R16 (2" of foam each side) ICF foundation, aligning the above-grade wall's foam makes for very low thermal bridging at the band joists, but an R20 (2.5") ICF can still work fine with 2" of foam on the frame-wall + rainscreen gap, with some flashing at the transition. Use Core-a-Vent &/or a mesh type screening at the bottom to keep the bugs & critters from setting up camp in the rainscreen gap, and it works a bit better if you detail some top vents to the rainscreen under the eaves.

   That's more than you asked, but your general concern is about moisture-management, so I went for it.

   Taking it even further afield...

   If you're off the natural-gas grid and were considering a propane furnace, note that at your power utility rates heating with ductless mini-split technology costs about 1/4 that of heating with propane, and with better than code-min windows one ductless head per floor usually works pretty good with an R20-ish whole-wall in your climate. (I have a relative in Port Orchard heating with a single-head mini-split in a less well insulated house than that, and it beats the ducted air predecessor hands-down on both comfort and operating cost.) With U0.28 or better windows and a <15% glazing/floor area ratio the room-to-room temperature differences won't get out of hand between the area with the mini-split head(s) and the doored-off rooms.

   If you build tight and have a heat recovery ventilation (HRV) system those differences can be further minimized by exhaust-only in the doored off rooms and supply only ducts to the area with the mini-split head, with jump-ducts or door grilles, etc for the ventilation supply to the doored off rooms. If you build tight you WILL need active ventilation, but building tight with HRV would further limit the mold hazards, since you would otherwise have some amount of mold risk at the infiltration/exfiltration paths.

3. 
   mathwonk | Sep 24, 2012 04:36pm | #3

   Wow! Thank you!