Air-Sealing Tapes and Gaskets
Which products stay sticky and flexible?
After this article was published, Martin Holladay conducted a test of eleven air-sealing tapes on a variety of materials. To read the results of Holladay's testing, see Backyard Tape Test and Return to the Backyard Tape Test.
It’s hard to create a tight air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both. without using tapes, gaskets, caulk, or spray foam. In this blog, I’ll look at two of these categories — tapes and gaskets. I’ll be focusing on air-sealing products, so I’ll ignore flexible flashing tapes used for waterproofing. (I'll address duct sealing in a future blog.)
I’d like this blog to be a work in progress, so I strongly urge readers to post information on products that work well.
A multitude of tapes
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 goodsMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. to a variety of materials, including concrete.
Needless to say, no single tape works well in each of these applications, so builders need to familiarize themselves with a range of products.
Sealing seams in housewrap or Tu-Tuf
Lots of manufacturers make housewrap tape. Manufacturers include 3M (Construction Seaming Tape #8087), Berry Plastics (Barricade Seam Tape, Nashua Seam & Seal Construction Tape #628), Dow (Weathermate tape), DuPont Tyvek (Tyvek tape — formerly sold as “Contractors' Tape”), Johns Manville (Seal-It Housewrap Tape), Typar (Construction tape), and Venture (Sheathing and housewrap tape #1585CW). Venture tapes are available from Energy Federation Incorporated.
Maine architect Jesse Thompson has high praise for Dow Weathermate tape; according to Thompson, it has a “good and strong adhesive, and is readily available.”
Most housewrap tapes work well to seal seams in Tu-Tuf ground covers.
Housewrap tapes have aggressive adhesives and are suitable for use on a variety of materials. If you’re not sure what tape to use for a particular application, you can always try housewrap tape.
Sealing polyethylene seams
Polyethylene can be tough to seal, especially because some manufacturers coat their polyethylene with a slippery, powdery substance that resists adhesives.
I’ve heard good reports about two Venture tapes that successfully seal polyethylene. The first is Venture #938, a clear polyethylene tape with an acrylic adhesive. This tape may not work with all types of polyethylene, however; if it doesn’t work, try Venture #1585CW sheathing and housewrap tape, a polypropylene tape with a cold-weather acrylic adhesive.
Many builders distrust tapes for sealing polyethylene seams. The time-tested method for sealing a poly seam is to lap the seam over a piece of framing lumber, and to install a bead of Tremco acoustical sealant at the seam. The airtightness of the Tremco sealant depends on the seam being compressed between the framing lumber and a subsequent layer of material (such as drywall or plywood).
For sealing seams in crawl-space ground covers (and for sealing ground covers to concrete walls), some builders recommend the use of fiberglass mesh tape embedded in duct mastic.
Taping rigid foam
According to some sources, housewrap tape is the best tape for seams in extruded polystyrene (for example, Dow Styrofoam). However, 3M representative Shawn Prestegaard recommends a different (and more expensive) tape for this application: 3M All Weather Flashing Tape #8067. This tape (#8067) is three times thicker than 3M housewrap tape (#8087).
According my backyard testing I performed in 2012 and 2013, the best tape for XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation. is Siga Sicrall.
For sealing the seams of foil-faced polyisocyanurate (for example, Thermax, Tuf-R, or Energy Shield), many builders prefer to use a foil-faced tape with an acrylic adhesive (for example, Venture 1520 or Venture 1521). Others use Dow Weathermate housewrap tape.
Sealing seams in OSB or plywood
Whether or not housewrap tapes are effective at sealing seams in plywood or OSB is a matter of debate. (All experts agree that taping OSB is more effective when the OSB has been primed.)
Many manufacturers of housewrap tape, including Venture, recommend their tapes for use on sheathing seams; other manufacturers, including Berry Plastics, advise builders that their housewrap tapes should not be used to seal plywood or OSB seams.
Tyvek warns against the use of Tyvek tape for sealing seams in plywood, OSB, or XPS foam. “The tape is designed to stick to Tyvek wrap,” said Alan Hubbell, a residential marketing manager for Tyvek. “Plywood and foam will expand at different rates from the tape, and over time it will crinkle and wrinkle and pull off.”
Jesse Thompson, a Maine architect, suggests using 3M All Weather Flashing Tape (8067) to seal plywood seams. “It's thinner and more flexible than Vycor,” Thompson said, “but seems to stick even better to rough surfaces, especially in cold weather.”
Marc Rosenbaum, a respected energy consultant who often advises builders to establish an air barrier at the exterior sheathing, doubts that the adhesives in housewrap tapes are aggressive enough to last the life of the building. Rosenbaum prefers to use a rubberized asphalt product (in other words, peel-and-stick tape like Grace Vycor) — a more expensive option than housewrap tape, but likely to be more durable.
Ben Cross, a marketing manager for construction products at Berry Plastics, recommends that OSB or plywood seams can be sealed with either Barricade #732 butyl peel-and-stick tape, or with Nashua #330X Extreme Weather tape, a foil-faced tape with an aggressive acrylic adhesive.
Another option for sealing sheathing seams is ZIP system tape, a tape designed to be used with proprietary OSB panels called ZIP System sheathing.
Sealing SIP seams
Most manufacturers of structural insulated panels (SIPs) recommend a belt-and-suspenders approach to air sealing. Seams should first be sealed with spray foam; later, interior seams should be taped.
One manufacturer of SIP tape is R-Control.
Gaskets are better than caulk
When builders first learn about air sealing, they often depend heavily on caulk. After inspecting a home for leaks during a blower-door testTest used to determine a home’s airtightness: a powerful fan is mounted in an exterior door opening and used to pressurize or depressurize the house. By measuring the force needed to maintain a certain pressure difference, a measure of the home’s airtightness can be determined. Operating the blower door also exaggerates air leakage and permits a weatherization contractor to find and seal those leakage areas., however, they learn that caulk has a few downsides. That’s when they usually graduate to gaskets.
If you are following the Airtight Drywall Approach — that is, establishing an interior air barrier — gaskets are particularly useful. Typical locations for gaskets include:
- Between the top of the foundation and the mudsill;
- Between the subfloor and the bottom plate;
- Between the window frame and the rough opening;
- Between the bottom plate and the drywall; and
- Between the top plateIn wood-frame construction, the framing member that forms the top of a wall. In advanced framing, a single top plate is often used in place of the more typical double top plate. and the drywall.
For sealing cracks around windows, Conservation Technology recommends the use of “gap gaskets.” The two most useful sizes are #BG44, a 13-millimeter gasket that seals gaps from 1⁄4 inch to 1⁄2 inch, and #BG46, a 21-millimeter gasket that seals gaps from 3/8 inch to 3⁄4 inch.
Conservation Technology also sells Teno Tape, a “tacky rubber double-stick tape supplied in 3/4 inch by 132 foot rolls” that is “best for general-purpose seaming, provided there is a firm surface behind the seam so pressure can be applied to the tape.”
Iowa builder Rollie Peschon is a fan of Denarco gaskets. “I use Denarco SureSeal gasketing in between the plates and the subfloor,” Peschon wrote on a Web forum. “It’s a 3/8 by 3/8 inch, open-cell, urethane-impregnated gasket that becomes airtight when under at least 60% compression, I believe. Being open-cell allows it to be compressed to almost flat, yet still remain resilient if there is some shrinkage of the framing members. We tried closed-cell gaskets, but when remodeling later, found that once they are under compression, the closed cells were ‘popped,’ leaving the gasket with no memory. Denarco also has a UltraSeal, which is 3/4 by 3/4 inch gasket that we use for between sill plates, and top of foundation walls, where the potential for a larger leakage area is greater.”
Illbruck Sealant Systems sells Willseal 600, a pre-compressed, self-expanding polyurethane foam gasket. “It’s an impregnated sealing tape that comes in different widths,” says Hans Porschitz, a building systems associate at Bensonwood Homes in Walpole, New Hampshire. “It’s a memory gasket. As it gets warm it swells up and seals the joint airtight.”