Air-Sealing Tips for Efficiency That Lasts // Part 3: Planning for Intentional (and Some Unintentional) Holes in the Air Barrier
This is part 3 of a series that describes how to air seal the most difficult parts of buildings.
We’ve emphasized throughout this series that continuity is the top priority for your air barrier. Holes and penetrations are the enemy. So how do we deal with doors, windows, and utilities—“holes” that are necessary for the design of a habitable building? Even a perfect air barrier must have penetrations for windows, doors, electric cables, water and sewage lines, telecom lines, and ventilation. Beyond these indispensible penetrations, some buildings have to be designed to accommodate pet doors, appliance exhausts, and fireplaces. Although we think you can and should limit or eliminate as many penetrations as possible from that second list, the first can’t be shortened. Good planning and workmanship at these penetrations is critical to ensure robust air barrier performance.
As a general rule, we recommend that you reduce and collect penetrations. Every planned penetration is a possible site of air barrier leakage and a construction challenge; the fewer you have to manage, the better. Try to eliminate as many penetrations as possible, and bundle the ones that you need as much as you can. For those must-have penetrations, good planning and smart sequencing will make the process of bundling go much more smoothly, and will ensure that you have a high-performance air barrier for years to come.
Even if you use airtight high-R-value triple-pane windows and high-performance doors, your air barrier will be compromised if these windows and doors are not continuous with the rest of your air barrier. A poor installation can reduce overall performance of the assembly significantly—so what’s the use of investing in high-performance windows if they aren’t properly installed? Here are the products and techniques that we recommend to ensure reliable airtight connections between your windows and the rest of your air barrier.
It’s tricky to plan a simplified connection when juggling bucks, sills, thermal bridging issues, and a variety of details specific to each window manufacturer. We have found that the best method is to use solid acrylic adhesive tapes. They adhere to a wide array of materials, and can therefore serve many different functions on the jobsite. Solid acrylic adhesives aren’t water soluble, so the seal won’t be affected by moisture over time. And perhaps most importantly, some of these tapes can survive for the lifetime of your building. Make sure to ask your supplier for supporting evidence of long-term durability [link: https://foursevenfive.com/what-we-mean-by-permanently-airtight/].
To help describe our methodology, we’ve developed a few terms of art for taping windows. Face-taping involves running tape along the interior or exterior face of the window frame and over the buck or sill after the window has been placed into the rough opening. Zero-reveal-taping involves pretaping around the outside edge of the window before it has been placed into the rough opening (see Figure 1). In this method, you run the air barrier into the rough opening and then attach the prepared window to the air barrier once it has been fastened into the window. Zero-reveal-taping leaves your window jambs clean and free of visible tape. It also facilitates a tight connection by allowing you to apply tape around the outside of the window frame before it’s inserted into the rough opening. Some Pro Clima tapes have adhesive strips that facilitate this multistep taping process, and these pretaped windows are the best guarantee of a long-lasting, high-performing air barrier. If you are using a flexible air barrier, folding that membrane into your rough opening and taping to the barrier rather than to the sill itself will further ensure continuity in your system (see Figure 2).
Continuous Window Seal
Effectively taping airtight window frames is the most important part of ensuring air barrier continuity at these penetrations. But a number of other steps should be taken to ensure continuity as well.
Plywood end grain leaks. If your window bucks are plywood, the end grain isn’t airtight. Tape your window to the buck all you want, but if the buck itself isn’t airtight, it’s going to be drafty. Taping the plywood end grain, the interior corners of the buck, and even over window clips ensures a robust air barrier and leaves no possible sites of air leakage unaddressed.
Read the labels. When using a material that’s new to you, make sure you know how to use it. Pro Clima tapes are pressure-sensitive adhesive (PSA) tapes, meaning that the adhesive is activated and the seal is set when pressure is applied. One benefit of this is that you can adjust the tape when you apply it—as long as you haven’t pressurized it yet. Unfortunately, problems can arise if the tape isn’t applied properly, though they can usually be easily rectified with a little pressure.
Pre-make tape corners to simplify. Corners are challenging. If you pre-make corners out of tape, windows can be easily and fully connected to window bucks, ensuring that even at the difficult junctions, your air barrier is continuous with your airtight window frame. This simple trick can save you time, headaches, and performance issues later on, so it’s well worth the effort and planning. Watch our brief video tutorial here.
Use a primer if you’re taping to an uneven or porous surface. It doesn’t matter how airtight your connection is if you’re taping to a material that isn’t itself airtight. For example, rough, uneven masonry isn’t an ideal surface for taping. By priming such a surface and filling in all of the cracks and air barriers, you ensure a robust, airtight connection between the tape and the surface—and therefore between the window and the rest of your assembly.
Choose high-performance windows and doors. It may seem obvious, but it’s critical that your windows and doors be airtight and well insulated. Inert-gas-filled triple-pane windows with panes separated by superspacers are the best performers out there, and triple-gasket sealing for operable windows ensures that when your window is closed, it’s airtight. Although it’s true that these windows and doors cost more, that cost is more than offset by the energy savings associated with a robust air barrier, the increased longevity of your building, and the peace of mind that these high-performance materials ensure.
Pipes and Wires: Use Appropriate Tools to Ensure Air Barrier Continuity
Utility pipes and wires that run straight through your air barrier can present significant air-sealing challenges. We’ve found that gaskets are the best solution for running these pipes and wires through your building envelope. Airtight EPDM gaskets, which fit snugly around circular (or near circular) penetrations, can be taped airtightly to your air barrier and used interior or exterior for every duct, pipe, and wire. Gaskets form a seal that is tight but flexible and isn’t compromised by the movement of pipes or wires—you can pull a mile of wire through one of these without springing a leak. These gaskets will take care of the majority of point penetrations. The rest (such as square or irregularly shaped penetrations) can simply be taped.
Multiple utility lines can be bundled together and funneled into your building, minimizing the overall number of exterior penetrations. But once they’re through the exterior, they should be individually gasketed through the air barrier. Dan Hines, of Habitat for Humanity DC, came up with a great method that he discusses in one of our videos. He bundled multiple utility lines into a PVC pipe through the exterior sheathing, and then split the lines for individual penetrations through the air barrier so that each could be tightly fitted with a gasket.
Although some people may advocate using foam around wires, pipes, and tubes to seal holes in the air barrier, foam is not ideal at these junctions. Bundling wires becomes impossible, as small air gaps between tubes end up becoming major leaks. What looks like a complete seal really isn’t. Foam cracks and shrinks over time, so any air seal is temporary. And because foam is inflexible, it doesn’t allow for wire movement. Flexible gaskets are a far superior choice.
Other Strategies to Minimize Penetrations
Beyond the means and methods described here, there are other steps you can take if you want to compete for tightest building in state. Choosing appliances wisely can help to eliminate penetrations. An electric stove and water heater, for instance, will eliminate the need for a gas line, and a condensing dryer provides an alternative to a vented dryer system. These up-front investments will pay dividends in the long run; the tighter the air barrier, the longer the life of the building, the better the occupants’ health, and the lower the heating and cooling costs.
To learn more, go to www.foursevenfive.com.
Finally, it bears repeating: Good planning and smart sequencing can make all the difference. By making smart decisions during the planning stages and by building deliberately and carefully, you can make small but powerful choices that will dramatically improve the simplicity, longevity, and performance of your air barrier.
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