Understanding the Critical Role Air Barriers Play in the Wet Pacific NW Climate
With energy costs showing no signs of abating, architects and builders everywhere are factoring energy efficiency into every aspect of their projects. Indeed, minimizing energy use is a key component of building standards gaining in popularity among policy makers, home building professionals, and homeowners alike.
In the U.S., nowhere is this more apparent than in the Pacific NW, which continues to lead the way in the adoption of such energy-efficient building standards. The Built Green® program, a non-profit, public-private partnership between the Master Builders Association and several Washington counties and agencies, is one of the country’s most successful initiatives that sets forth guidelines for green building certification. In Oregon, Earth Advantage leads the way with it's stringent certification program and push for zero energy and zero energy ready construction. When building new homes in this progressive market, energy efficiency isn’t just an afterthought – it’s a core design principle. And ensuring an effective, continuous barrier between a home’s interior and the famously wet environment outside is a top priority.
But how can builders create the “tightest” envelope to minimize air leakage and energy use? And how can they achieve this tightness while preventing condensation in their wall assemblies, a common cause of mold, mildew, and structural decay?
Conner Campanella, Residential Building Envelope Manager at Henry® Company, provides some insight into understanding the role house wraps play in the construction of a home to ultimately help make it energy efficient as well as protect the inside from the outside elements.
Why do homes need a housewrap? What is the primary benefit of a housewrap?
Homes need a housewrap for two main reasons – to create an energy-efficient structure and protect what’s inside from the outside elements.
A home would not be energy efficient if it only consisted of siding, sheathing, insulation and drywall. All of these products are susceptible to something building scientists call “Diffuse Flow and Channel Flow.” Diffuse flow is when air travels through porous materials or materials whose characteristics are not intended to prevent air infiltration. Diffuse flow is common and often is accepted among these materials because they are not intended to be an air barrier. The bigger problem is channel flow. Channel flow is when air seeps through the cracks, holes, breaks and imperfections in a structure’s walls. Gaps in sheathing, nail holes, pipe and vent penetrations, the mudsill, etc. are most susceptible to channel flow damage. Not only does channel flow contribute to expensive heating and cooling, but it also allows vapor/humidity into the home. With vapor/humidity entering the wall cavity, you now have to worry about water and mold damage.
Why is the installation of a housewrap just as important as the housewrap itself?
Quick and careless installation of housewrap is very common. Improper laps, incompatible sealant use, incorrect installation around pipes and penetrations, mismanagement of rips and tears, and poorly taped seams are all too common. Some of these issues are on the installer, but many are the result of poor communication amongst other trades. For example, common issues include plumbers cutting into walls in order to pass pipes into the house and not sealing the penetration correctly, or roofers applying underlayment over the house wrap and not addressing laps properly.
Another problem we see in the field is when builders leave the house wrap exposed for extended periods. Not only do you have issues with UV rays breaking down the material, but wind creates bigger holes where the staples are fastened to the wall, allowing water to flow behind the mechanically attached house wrap. Some house wraps aren’t breathable enough to allow it to escape. How seams are taped is another common issue. Seam tape starts to lose its effectiveness as it is exposed to rain over time. The adhesion begins to wear off and water can flow behind the house wrap, ultimately making it less efficient.
What makes your housewrap different than what is offered by other manufacturers?
Henry® Blueskin® VP100 Self-Adhered Water Resistive Air Barrier Membrane, a vapor permeable air barrier, adheres directly to the sheathing, eliminating holes created by the staples used to attach traditional house wraps. Also, Blueskin® VP100 is self-adhered, allowing it to bridge the gaps of the sheathing. A 2,500-sq. ft. home has over a half mile of gaps in the sheathing. Those gaps can directly result in energy loss and moisture issues, as well as create an easy entrance for insects. Many older homes have poor to nearly no insulation in the wall cavity. Often replacing or adding to your interior insulation is not an option when residing or remodeling your home. Blueskin® VP100 will help a home’s insulation perform at its intended R-Value while contributing to reduced energy costs and eliminating uncomfortable air drafts. On top of all that, Blueskin® VP100 includes a self-sealing technology, automatically creating a seal around nail penetrations and eliminating additional areas for water and air infiltration. Traditional “mechanically fastened” house wraps cannot make this claim.
Does the performance of your housewrap depend on the climate in which it is installed?
Henry® Blueskin® VP100 Self-Adhered Water Resistive Air Barrier Membrane, a vapor permeable air barrier, is engineered to work in all climates regardless of the temperature and moisture levels both inside and outside the home. From below freezing temperatures in Canada to sweltering summers in Arizona, Blueskin® VP100 helps keep heating and/or cooling working efficiently. Blueskin® VP100 seals around siding nails and allows homes to breathe from the inside out.
Does the performance of your housewrap depend on the cladding that will be installed?
Generally speaking, no. In fact, Henry® Blueskin® VP100 Self-Adhered Water Resistive Air Barrier Membrane, a vapor permeable air barrier, can extend the lifespan of the material and finish of your cladding. Blueskin® VP100 creates a natural air gap between stucco and masonry products that allow water to drain down and air to flow between the sheathing and the cladding. Blueskin® VP100 is a certified drainage product, which means it will help dry out whatever cladding is installed on the home.
What other factors do you take into consideration when developing your new housewrap?
Hygrothermic issues, breathability, U-Value and R-Value enhancements, decreasing the effects of wind-washing, drainage, and ease of use.
What trends are you seeing in housewrap? How does your new or most recent housewrap address those trends?
Many housewraps will find it difficult to meet the new ICC-2015 code for air barriers which focuses on air leakage. Traditional housewraps require staples to adhere it to the wall and all seams to be taped which might impact air tightness. Henry® Blueskin® VP100 Self-Adhered Water Resistive Air Barrier Membrane, a vapor permeable air barrier, eliminates those staple penetrations and seam tapes, all while offering a self-sealing technology that seals around siding nails.
What materials or resources do you offer contractors to make sure that they install your housewrap correctly?
The Henry® Company offers videos posted at www.Henry.com showing proper installation of our product and addresses common applications like window details and pipe penetrations. If the job is within driving distance of a Henry® representative and reasonable notice of the application date is provided, a Henry® representative will spend time on the jobsite applying the material with the crew. They will go over every detail applicable to the job and leave behind a general installation guide. The Henry® representative will also have step-by-step guides and pictures that they can provide.
Additionally, some lumberyards have personnel who’ve undergone installation training by The Henry® Company. These lumberyard employees will walk through installation best practices with you when you purchase material from them.