How To Prepare For High Performance Windows
Windows might make you nervous. They're often big and heavy, yet fragile. And in a high performance building, windows are the most expensive components.
But that investment in great windows has a big payoff as well. High performance windows deliver on interior comfort and building efficiency - so you don't have to rely on energy-sucking HVAC systems to make you comfortable. Whether it's heating your home in winter while keeping out the cold, or preventing overheating in summer - high performance windows perform many core building functions. And unlike HVAC systems, windows have zero operational costs and no machines that will inevitably break.
Your Windows Are Nice, But How's Your Install?
When you pay for all that performance, you also want to make sure windows are properly installed. It's not just about protecting your highly engineered, triple-gasketed, triple-paned window investment. It's also about your building enclosure: one wrong move and your exterior walls can also suffer expensive damage. You need window installations that are airtight and correctly flashed - and as a result will last forever. For optimal window installs, you also need to account for vapor drive at different times of year, and take steps to super-insulate the window frames for the best thermal performance.
Even if you didn't spend a fortune on your windows, a proper window install will bump up your building's comfort and efficiency, while ensuring that your walls stay dry. This post provides the tools for simple and effective high performance window installations.
The words we use to refer to window sealing tapes may be a little different from what you've heard. So let's first review our terminology. The fact is, windows come in untold varieties - many of them with different installation requirements. Therefore 475 provides a number of different tapes to deal with all the possible conditions.
In the diagram above:
- Method of Connection is the way windows are taped for airtightness and moisture control. Most windows are Face-Taped (upper left), in which tape is bonded to the front face of the window frame after the window is installed. Increasingly, high performance windows are Zero-Reveal-Taped, where tape is bonded to the outside of the window frame before the window is installed (this is explained below).
- Adhesive Surface describes which parts of the tape contain adhesive. Full-Surface Adhesive tapes have one full side coated in adhesive from edge to edge (with continuous or split-release backing paper). Adhesive Strips tapes come in different flavors. Some adhesive strip tapes are actually narrow membranes with several adhesive strips.
Tools of The Trade:
- Vapor Permeance: 8 perms (vapor open)
- Interior/Exterior: Both
- Method of Connection: Face-Tape
- Adhesive Surface: Full-surface
- When to use: Excellent all around window tape for face-taping at interior and exterior. Tough fabric backing and easy to use. Sticks great to all surfaces including OSB & plywood sheathing.
- Vapor Permeance: Vapor closed
- Interior/Exterior: Exterior
- Method of Connection: Face-Tape
- Adhesive Surface: Full-surface
- When to use: At every window sill. ENCORS is the ultimate self-sealing, waterproof sill protection. Super flexible for continuous leak-proof sill pans. Great for connections to masonry.
- Vapor Permeance: EXO = 38 perms; SL = 1.4 perms
- Interior/Exterior: EXO for Exterior
- Method of Connection: Zero-Reveal-Tape or Face-Tape
- Adhesive Surface: 3 adhesive strips
- When to use: When you want the most vapor-open exterior and vapor-retarding interior, and like the option of either face-taping or Zero-Reveal-Taping. Ideal for connecting to interior and exterior membranes. Use Primer RP or CONTEGA HF caulk when connecting to rough or uneven surfaces.
- Vapor Permeance: EXO = 8 perms / SL = 1.2 perms
- Interior/Exterior: EXO/EXO-D for Exterior / SL-D for Interior
- Method of Connection: Face-Tape or Zero-Reveal-Tape
- Adhesive Surface: EXO = Full-surface EXO-D & SL-D = Full-surface + 1 adhesive strip on opposite side
- When to use: When you're really serious. Modified solid acrylic adhesive doesn't need a primer, even with masonry. Thin fleece backing is great for integrating into plaster. SOLIDO EXO-D / SOLIDO SL-D have an additional adhesive strip for Zero-Reveal-Taping.
- Vapor Permeance: ~6.5 perms
- Interior / Exterior: Exterior
- Method of Connection: Zero-Reveal-Tape
- Adhesive Surface: Full-surface expanding foam for Zero-Reveal-Taping
- When to use: When you want to use an exterior expanding foam, and you're using one of the above interior airsealing tapes. FIDEN is "windtight", which means it's airtight in the real world, but will allow air through when pressurized with a blower door test.
Zero-reveal-taping is the simplest and most robust way to air and weather seal. Pro Clima has put a lot of thought into airtight window installation methods, and it's the only company that offers additional adhesive strips integrated into their tapes to simplify Zero-Reveal-Taping. They figured out that you can save an incredible amount of time by doing much of the airsealing and flashing BEFORE the windows are installed into the rough opening.
Whether by necessity or choice, Zero-Reveal-Taping allows you to leave the window jambs free of tape. In the photo at left, an aluminum-clad window is Zero-Reveal-Taped at the exterior with CONTEGA SOLIDO EXO-D. First the back-side adhesive strip is attached to the outside of the frame. Then after window installation into the rough opening, the full-surface adhesive connects to the SOLITEX MENTO 1000 airtight housewrap/WRB.
The diagram on the right shows how to do the pre-install taping:
- Set the windows on saw horses.
- Remove one adhesive strip and bond all the way around the outside of the frame, ending back where you started. Leave extra material at corners as shown.
- Flip it over and do the other side. You can leave the remaining release strips on the tape - they'll be ready to attach to your air barrier at a later time.
Get Faster and Better: Think Before You Start
It's a good idea to prep your buck and your hardware before you jump into airsealing the window itself. Sequencing can make all the difference between a complicated job, and a fast and sturdy job.
Below are some lessons learned on the interior side of a window installation:
- On the left, Plywood endgrain leaks - so tape it! An easy but important step.
- On the right, we've used TESCON PROFIL to tape our plywood endgrain, as well as the inside corners of the window buck. If your buck isn't airtight, and you then tape to it, your window isn't airtight either!
- Another lesson here: we taped the window fixing clips after the window was secured, but before we face-taped the window with CONTEGA SOLIDO SL The sharp edges of the fixing clips can cause a pathway for air under the tape. Remove those leaks by covering the clips with TESCON PROFIL, TESCON PROFECT or TESCON VANA before you airseal.
Pressfix, Pressfix, Pressfix
A Pressfix is a little blue square that you should always have in your pocket when you're working with Pro Clima tapes. Remember, these are Pressure Sensitive Adhesive (PSA) tapes, which means that the adhesive is activated with pressure.
Pressure activation works to your advantage on multiple levels. First, it gives you time before pressurization to carefully and precisely place the tapes. If it's not exactly where you want it, you can pull off the tape and re-position it. Only when you pressurize is the adhesive activated - and grows stronger over time. Pro Clima tapes have been advance age tested to hold for 100 years. That century begins when you pressurize it.
Pressurization also helps with the smallest details. Once your tape is in the right place, to finish the job you often need to pressurize the tape into the tight corners and small crevices that are found everywhere on windows. Our fingers aren't well-suited for this intricate work - but the Pressfix is. As an example, take the window shown at left. The way the frame is mitered at the corners leaves a tiny passageway for air to leak. With a little swipe of the Pressfix edge, it's pressurized and airtight.
Windows are often the weakest link in your air sealing, so taking a moment to re-inspect the details while you're taping will allow help you avoid searching for that leak during the blower door test.
Now you've got the tools you need to look at a window and judge the best method for weatherproofing and airsealing. You still need to get your hands dirty and wrap your head around a real installation. We've got plenty more to get you covered. Soon to come: another blog post on window installation case studies, which we'll link here when completed. Also check out some of the following videos to help it all sink in.
- Pre-Make Your Window Corners: If you're face-taping with TESCON PROFIL, TESCON PROFECT or CONTEGA SOLIDO tapes, pre-make your corners for the tightest, cleanest window corners on the block.
- Install EXTOSEAL ENCORS to prep your sill: We show a couple of different options. Watch Floris show the basics of using EXTOSEAL to cover the sill and face-tape to the bottom of the window frame. Or watch Chris Corson of EcoCor in Maine cover a rough open sill in preparation for a floor-to-ceiling window.
- Watch How Real Builders Do It: We have a variety of videos that look at window installations in the real world. One of our favorites was with Chad Mathrani of Vermont Natural Homes. He guides us through his installation that uses CONTEGA EXO to connect his window bucks into exterior plaster, and EXTOSEAL ENCORS at the sill.