Net Zero Energy Virginia Home and best practices...

As you tighten the envelope of the home, control of moisture becomes much more important, and standard practices become too low a target. the last thing you want is to have your tight envelope trapping wayward water. The dark material you see here coming up behind the brick is 30lb felt underlayment. Although the SIS already forms a vapor barrier, our builder, Mark Waring, prefers the redundancy of additionally installing the felt on top of the SIS.

The green material you see is GreenGuard® RainDrop® Housewrap.
RainDrop’s innovative drainage channels keep water out of the wall system. The channels won’t crimp, collapse, or flatten, ensuring water will drain no matter how tightly cladding is nailed to the wall. Because it’s not perforated, RainDrop resists air and water infiltration. Plus it breathes to allow moisture vapor to escape. With its high tear resistance and translucent design, installation is quick and easy with no job site waste. And it stays UV-stable up to 4 months. RainDrop is an ideal secondary weather barrier for fiber cement, vinyl, foam-backed vinyl, and wood sidings and meets the National, Standard, Uniform and International Building Code requirements for air barriers, moisture protection barriers and weather-resistive barriers. It is used on top of the SIS and behind any of the areas to be covered with shingling.

ZEH, SIS, and other energy-friendly acronyms to know

The envelope of the house is rapidly developing, so its time to highlight a few key products. The house will have an exterior sheathing of a new product from Dow, Styrofoam SIS (Structural Insulated Sheathing). Winner of the 2009 Green Product Awards from Building Products Magazine, STYROFOAM SIS™ Structural Insulated Sheathing from Dow combines a structural layer, a moisture barrier, and foam insulation, providing R-values of 3.0 at ½ inch or 5.5 at 1 inch. Made of up to 80 percent post-consumer recycled content by weight, STYROFOAM SIS™ Brand Structural Insulated Sheathing is ENERGY STAR-qualified. And, at one-third the weight of OSB†, it is easier to handle and quicker to install. One judge summed up the products benefits as, "This appears to be an excellent product, providing wall bracing, energy performance, and the potential for weatherization all in one. The labor savings alone is huge." Our builder chose to use the 1/2 inch product, after an analysis revealed relatively little energy gain for the thicker product in our build (rule of diminishing returns). The panels are nailed or stapled in place to the outside of the studs and the seams are taped with WEATHERMATE™ Construction Tape (2-7/8" wide) .

WEATHERMATE Construction
Tape is pliable, ensuring a tight
seal, even at extremely low

temperatures. The oriented
polypropylene backing is
formulated with a UV-treated
film to help resist degradation
from exposure to sunlight.

The garage is not insulated, but covered with WEATHERMATE™ Plus – Housewrap to serve as an air and moisture barrier. It is significantly superior in water resistance, air porosity, vapor permeability and tear resistance than the more commonly used Tyvek. It also possesses prolonged UV ray resistance, allowing it to be exposed up to 120 days before significantly degrading (hopefully our garage will not test that limit).