Walls and Insulation
Energy Efficient Walls “Dress in Layers”
Driving through new subdivisions, you’ve probably seen homes wrapped with a home wrap and maybe some that weren’t. That’s because there are many ways to frame and insulate a home – many of which are not the best way, but they’re less costly initially. Yet, in the long run, end up costing homeowners extra money in energy bills, and potentially, in home repairs.
It may help to think of new home construction in grades such as good, better and best. Here are the five essential “tools” for constructing the best wall system for our region:
- 2x6 wall studs at 16” on center. – 2x6 vs. 2x4 wall construction allows more space for insulation, resulting in a more efficient home. Don’t be misled – the benefit of studs at 16” OC vs. 24” OC is additional strength.
- R-board sheathing. R-board applied to stud walls with metal wind bracing creates a continuous surface of insulation along the entire exterior. An R-3.5 insulation rating increases the home’s energy efficiency and is superior to an exterior wall made of OSB, which is not insulated. An alternative is polystyrene insulation (i.e. styrofoam) over OSB, but this product is not as durable and is easily punctured during construction. Some also use polystyrene without home wrap to cut costs, but it’s not a wind or water barrier.
- Tyvek HomeWrap over all exterior walls. Tyvek should be wrapped over the entire house, including gables and the garage. Tyvek resists bulk water and air penetration while allowing moisture vapor to pass through. Often it’s is not used on the garage, but why would water penetration be acceptable in the garage, or in the bonus room above it? Moreover, most siding manufacturers require a home wrap behind their product to maintain their warranty.
On the left, a home with Tyvek HomeWrap properly installed all the way to the gables, covering the garage and wrapped around the inside of window openings. The home on the right is an example of what not to do -- an example all too common in many subdivisions.
- Extra protection at windows. Look closely around the windows of homes under construction – note how the windows are installed. If there’s a way for water to get in, it’s usually at windows and doors. The DuPont™ Flashing System provides an extra layer of protection. One of the components, Straightflash™ tape, creates a heavy-duty seal to prevent driving rain from penetrating the heads and jambs of windows. FlexWrap under window sills and doors prevents moisture from entering the home’s interior. To be effective, the framing must be constructed with the proper pitch to help water drain away from the interior.
- Above average insulation. In Wisconsin, insulation isn’t a place to cut back. The industry standard insulation is R-19, but an R-21 high-density fiberglass batt insulation installed between wall studs is the premium grade. Combined with the R3.5 exterior sheathing, the wall system has a total of insulation rating of R-24.5. Some feel that newer blown-in cellulose insulation is a better alternative, but with cellulose or even foam insulation you have to weigh the cost/benefits.