Previously, we discussed how to choose the right kind of flashing tape, but another key consideration is installation. These days, every manufacturer seems to have a specific set of installation guidelines that must be followed to uphold each respective product’s warranty. Sounds easy enough, but there’s not one single “correct” way. Guidelines will vary between manufacturers, making a contractor’s job that much more difficult. When in doubt, though, follow the manufacturer’s instructions. The International Residential Code (R613.1) requires windows to be “installed and flashed according to manufacturers’ instructions.” If there’s ever a problem, you’ve done what was required by the building code.
The folks at Fine Homebuilding give a fantastic tutorial here: Installing and Flashing Windows Correctly
When it comes to using flashing tape with these installations, temperatures and compatibility of materials is critical, especially on hard to bond materials. We’re going to cover the basics below, but you can also find great information and case studies here and here.
Temperature. Again, weather and temperature play a critical role in installation. Why? Well, modified-bitumen products do not fare well in cold weather. Most become less sticky at around 50°F and will not stick well below about 40°F. Unless you are working with a tape product specifically formulated for low-temperature usage, a butyl- or acrylic-based product is a better choice in cold weather.
High temperatures can also be a problem. For example, standard modified bitumen can ooze at high temperatures, especially when installed under metal exposed to direct sunlight. For example, under metal roofing or on south- or west-facing windows. In general, butyl tapes are more stable at higher temperatures, but also have upper limits. Unless specially formulated for high temperatures and labeled as such, flashing tapes can begin to soften at somewhere between 120°F and 180°F. Some high-temperature formulations made for commercial applications can tolerate temperatures over 200°F, but are generally not as sticky and may be difficult to find. If the manufacturer does not publish the highest temperature value, contact them directly or look for another product that does.
Substrates. Each manufacturer specifies which products are safe to stick to and which require special attention. Generally speaking, solid wood, plywood, vinyl, and metal are usually fine as long as they clean, i.e. free of oil, dirt or dust. Some manufacturers suggest that concrete, masonry, and OSB will have better results when primed, while others will recommend that all substrates be primed for best performance, especially in cold weather
That said, it’s worth noting that priming is only one solution; if you choose the right tape, you may be able to reduce this step and save labor.
Shingle. According to Building Advisor, you can’t go wrong following the shingle principle: “Given all the factors that can affect the longevity of an adhesive bond, it’s best not to rely on on a taped joint to keep water out of your home’s exterior. Every flashing detail, adhesive or not, should follow the age-old “shingle principle.” In this approach, the upper material is always lapped over the lower material so water will naturally flow down and away from the building structure, even if the adhesive bond fails. This is how materials like roof shingles, cedar shingles, and horizontal sidings work – they shed water naturally. Peel-and-stick flashings still simplify many flashing joints, but they are not magic.”
All told, when it comes to flashing installation and choosing the right adhesive, keep in mind that moisture management is the major consideration with any type of airtight construction. Alex Lukachko, a researcher with Building Science Corp., recommends making sure that subconctactors clearly understand the importance of maintaining a continuous drainage plane and the continuous air barrier.
“For each hole in the building enclosure, subcontractors need to know that the hole is a break in the continuous rainwater control, air flow control, moisture control and thermal control layers in the building enclosure,” says Lukachko.
Lukachko recommends sealing penetrations on the interior with low-expanding foam sealant or caulking, depending on the size of the gap that needs to be filled. On the outside, flashing and flashing tapes are used as part of a well-constructed weather resistant barrier.
Diligence paid to sealing techniques, whether in windows, doors or elsewhere is crucial in creating an airtight enclosure and achieving the energy performance.
Be sure to keep reading the ECHOtape blog for more on flashing tape.