“Build it tight, vent it right.” It’s a phrase commonly used by high performance building experts to describe the two most crucial design tenants of energy-efficient home construction. Without a virtually airtight, well-insulated building envelope, achieving the energy performance levels now required by building codes is nearly impossible without a massive investment in renewable energy systems.
The good news for builders is that air sealing the building envelope right is one of the lower-cost, higher-return investments when designing for net-zero performance. It all boils down to good building practices.
What Is Air Sealing and Why Should You Care?
In a typical residence, there are nearly 5,280 feet of potential problems. That’s one mile of exterior joints that can leak air, increasing heating and cooling costs while allowing moisture, cold drafts, and unwanted noise to enter a house. The solution? Air sealing.
Air sealing ensures that all the effort put into constructing a tight and well-insulated structure, doesn’t go out the window (… or through the walls, ceiling, or foundation …) due to leaks that create an unwanted exchange of interior and exterior air, heat, and moisture.
What does that matter? Because air leakage…
- Is typically the largest driver of energy use in the home, comprising 30% -70% of energy wasted on heating and cooling;
- Is is usually the biggest cause behind drafts, hot/cold spots, and other comfort issues in your home;
- And, is often the largest contributor to moisture problems, especially mold and mildew.
Plus, stringent new IECCC 2015 building codes make air sealing a priority for construction professionals. Indeed, for builders and contractors in California, Title 24’s ambitious policy is that all new homes be designed for net-zero-energy operation by 2020. Once enforced, a mere two years from now, they will be the strictest air sealing codes in the United States.
So, at ECHOtape, we are spending a lot of time thinking and writing about air sealing, green building and sustainability. Obviously, because tape has an integral role in sealing the building envelope, so we’re heavily invested in developing products to meet the challenges imposed by stringent building codes. But there’s a second, more personal reason. When homes are air sealed well, they reduce noise from the outside; less pollen, dust and pollutants enter the home; there are less drafts; and your heating/cooling system is much more efficient. Sure, air sealing impacts the greater environment, but it’s means a lot more comfort for the homeowner… something I, personally, have come to really appreciate.
Why Air Sealing & Comfort Go Hand In Hand
My first Massachusetts home, a Victorian, was forever drafty during the winter and sweltering in summer. Over the course of 20 years, we worked to improve its efficiency, adding tons of insulation, replacing windows, getting a high-efficiency boiler, putting in an A/C system and installing a gas stove. The effects were minimal at best. We were constantly turning things on and off in a desperate attempt to get comfortable.
Turns out, because older homes are not air sealed properly, it’s virtually impossible to manage temperature. No matter what you do.
So when it came time to buy a new house, I was smarter. Or so I thought. My “new” dream house was a perfect, 1897 New England colonial, just the right size with the perfect yard for lots of gardening and enough room for a dog! The first order of business upon moving in? Insulation, updated thermostats and even solar panels. [I qualified for a great program by Solar City no upfront expense and for several months of the year, I generate more power than I use!]
Still, this lovely new home that is more “efficient” than the last, is nearly impossible to regulate so that all three floors are comfortable at the same time. On most days, it is often cold on the first floor, comfortable on the second, and too warm on the third. In the summer, the first floor is comfortable and often cool, the second floor is sweltering, and the third floor, suffocating.
All of this to say that I have come to understand that “comfort” is not the same thing as “efficiency.” By the same token, you can be “green” and not be energy efficient. There is only one way to ensure comfort and sustainability and efficiency in a home, and that is via proper air sealing.
What About Moisture Management?
We mostly think of air sealing as a critical step to prevent heat and cooling losses; but air sealing can also be an important means to prevent moisture and mold damages. Because moisture is transferred predominantly by air currents — accounting for more than 98% of all water vapor movement in buildings — air sealing your home is essential. Generally speaking, installing insulation reduces heat transfer, so it also moderates the effect of temperatures across your home. In most U.S. climates, properly installed vapor diffusion retarders can be used to reduce the amount of moisture transfer. Except in deliberately ventilated spaces such as attics, insulation and vapor diffusion retarders work together to reduce the opportunity for condensation in a house’s ceilings, walls, and floors.
Indeed, the potential for moisture problems exists anywhere building components are below grade, whether you have a basement, crawlspace, or slab-on-grade foundation. Most basement water leakage results from water flowing through holes, cracks, and other discontinuities into the home’s basement walls or water wicking into the cracks and pores of porous building materials, such as masonry blocks, concrete, or wood. These tiny cracks and pores can absorb water in any direction—even upward. To create an energy-efficient and comfortable living space in your basement, you will need to insulate as well as properly control moisture.
Many old codes recommended ventilation to prevent moisture damage; but that’s not the best approach to avoid moisture from getting into the house through the basement. Ventilation can help, in some climates, but is not a remedy and can make things worse, in moist climates. Building codes from 2012 forward require a comprehensive air barrier, ground-moisture barriers and water control around the home’s foundation as key elements of an airtight approach, intended to transform basements and crawlspaces into healthier and more comfortable spaces.
For more on moisture, humidity, mold and indoor air quality as it relates to air sealing, check out this post by Green Building Advisor.
Air Sealing Best Practices from High Performance Building Pros
Personal feelings aside, there are several techniques and considerations that we have found in our field research with builders that have proven to provide efficient air sealing – most of these add very little additional cost to new home construction, and require little to no specialized training.
That said, not all air leaks are created equal. As we heard throughout the 2017 IBS Builders Show in Orlando, builders really want to know where and what to seal to get the optimal result, pass blower door testing and meet new code standards. The best bang for the air sealing buck, if you will.
With that in mind, Owens Corning’s Building Science team conducted a comprehensive 12-month study that recorded and measured where and how air leakage occurs in a typical home. The result: an “air-leakage-bang-for- your-buck” ranking of every opening and joint in a home.
We suggest reading the full report here, but the five most effective air sealing regions are:
- Top Plate-to-Attic;
- Recessed Lights;
- Duct Boots;
- Band/Rim Joist;
- Garage-to-House Common Wall.
These key areas will yield the greatest amount of air tightening for a blower door test for the least amount of applied sealant.
ProBuilder.com presents another approach — to make air sealing your top priority, concentrate on insulation. “Focus on sealing the areas along the top and bottom plates, particularly around the perimeter in the attic area and along the foundation, whether it’s a basement, crawlspace, or slab, so that you’re not getting convective loops in your walls.”
The article highlights these five key focus areas:
- Continuous air barrier from the basement slab to the attic floor. That means the basement slab to the basement walls needs to be air sealed); the foundation to the floor system needs to be air sealed, whether through housewrap or another material; and the walls to the attic floor need to be air sealed. Anthony Grisolia, manager of quality and performance with IBACOS, advises builders to pay particular attention to the attic “lid,” or floor. “When we sealed that area in the Energy Efficiency Lab Home (a test home built near Pittsburgh), it was the biggest one-step decrease in infiltration,” he says.
- Advanced framing.Good structural design means less framing costs and more room for insulation in the shell.
- Proper insulationaround openings, even small ones like outlets and junction boxes. Make sure you’re both air sealing and insulating.
- Draft-stopping.When using fiberglass or cellulose wall insulation, it should be enclosed on all six sides. “Double walls, ceiling height changes, and areas behind tubs and showers are often missed,” says Rich Baker, building performance specialist with IBACOS. “The insulation should be sheathed with a rigid material and sealed around the edges.”
- Attic hatch sealing. Make sure the attic opening is fully gasketed and that the pull-down stairs, or door, come into full contact with the gasket to provide a thorough seal.
Last, but not least, using a simple checklist is helpful for systematically documenting every possible air leak during blower door tests. This Thermal By-Pass Checklist helps to identify areas that need sealing.
Top 10 Reasons Contractors Should Use Tape To Seal the Building Envelope
As customers demand more energy-efficient homes and building energy codes become stricter, more and more contractors are using tape to seal the building envelope and get the job done correctly. Today’s newer and higher-performing adhesive tapes offer builders better choices and multiple advantages over conventional building materials. These tapes actually stick better over time, are more durable and are more weather resistant. Indeed, modern adhesive technology is much more sophisticated as a whole.
But don’t just take our word for it. Here are 10 more great reasons to seal the building envelope with tape.
- No holes. Unlike nails or rivets, tape does not make holes. Less holes means less opportunity for air leakage.
- Clean, easy application. Unlikes liquid and foam sealants, tape is not messy and it’s easier to apply.
- It’s affordable. Using tape to seam is more affordable than spray foam or liquid adhesives.
- Versatility. Unlike other construction materials, tape has a unique ability to withstand extreme temperatures, harsh environments and to bond securely with a host of different substrates and materials
- It’s energy efficient. Using tape to seal the building envelope is standard operating procedure in Europe where passive house (a.k.a. Passivhaus) is the norm. Passive Haus results in ultra-low energy buildings that require little energy for space heating or cooling. In fact, tape experts cite Europe as the best example of overall utilization of acrylic tapes in construction. “In Europe, they tape up everything when building or retrofitting to create an air-tight seal,” says David Joyce, nationally known construction and tape expert, and owner of Synergy Companies Construction LLC. “Energy costs are much higher there, and it’s a matter of necessity.”
- The Department of Energy recommends it. Direct quote from Building Energy Code Resource Guide: To limit air leakage, builders use tapes to seal the seams of a variety of membranes and buildings products, including housewrap, polyethylene, OSB, and plywood. Tapes are also used to seal duct seams, to seal leaks around penetrations through air barriers — for example, to seal around plumbing vents — and to seal sheet goods to a variety of materials, including concrete.
- The Green Building Advisor is obsessed with tape. Check out these articles: Backyard Tape Test and Air Sealing Tapes and Gaskets.
- Leaders in performance building, like Matt Rissinger, use it all of the time. Check out Tight House Construction and 4 Tips to Building an Efficient , for example.
- And Hank Spies, who uses tape in metal roof sealing. Quoted here: The most effective approach is to seal all joints with butyl sealing tape… It is more effective than caulk, and since the butyl does not cure, it tends to creep within joints to absorb the movement of the metal with changes in temperature.
- Twice as nice. More and more builders are using double-sided tape as a housewrap tape so they can overlap seams and ensure no water gets through.
Like a windbreaker over a sweater, our homes need both good insulation and a continuous air barrier for the system to work right. As we build and remodel toward much lower energy use, construction professionals need to build skills in air sealing, blocking thermal bridges, and good thermal details to make houses really perform. Building codes may not demand it yet, but savvy homebuyers certainly will. If you’re need help finding the right seaming tape for air sealing, contact us. We love solving tape challenges!