Thanks to their preset thickness and impressive ability to shield a building envelope, sheet-applied air and vapor barriers are a favorite of many commercial installers. They’re a much more durable option than low-budget weather-resistant barriers.
But that doesn’t mean you’re totally off the hook for hard work. Sheet air barrier installation takes a little more prep time and carefulness vs. liquid-applied barriers. (Learn how to install those here.) The little details matter, and can snowball into serious quality issues if you rush your work.
Fortunately, with a little guidance, each step of the installation process is very doable, even if you’re fairly new to this construction product.
There are do's and don't’s for every step of the air barrier installation process:
As always, a successful construction job starts with setting yourself up for success.
Ready to work? In addition to the air barrier membranes themselves, you may need:
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Primer |
Improves adhesion |
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Roller |
Pushes sheet against substrate |
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Sealant & applicator |
Detail, prep work, & terminations |
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Cutting tool |
Detail work (penetrations, rough window openings, conduits) |
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Through-wall flashing |
Directs water away from interior & structural elements |
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Sheathing |
Rigid backing for attaching barrier |
Most, but not all, sheet membrane installation products require you to prime the sheathing. A primer makes the base more uniform and stable, reducing the risk of air leaks through gaps or poorly adhered sections. Most primers for self-adhered barriers come in roll-on form, but if you’re fully in fire-drill mode, track down a spray-on primer to speed up installation.
When you’re ready to cut the sheets themselves, a utility knife is a handy tool for getting clean, precise cuts in tough places. Some subcontractors use scissors if the material is especially thin or flexible.
Later in the project, a two-handed roller is a godsend. This tool will help you ensure 100% of the membrane attaches to the wall.
Before lining up labor, tools, and a schedule, make sure the environment looks conducive to the material you're using. Actually, your environment matters both in the lead-up phase and the installation date.
In the days leading up to installation, find acceptable storage conditions for your air barrier materials. Liquid-applied products are prone to job-site damage from:
Even on installation day, don’t drag the products out first thing in the morning and leave them naked and alone for several hours. Cover them up.
When the time to get to work is near, check the area’s:
One sheet barrier installation may have a different safe temperature range vs. another product. (Interestingly, it’s actually the detail sealant and any primer you use that limit the range, rather than the sheet itself.) Most sheet materials tempered indoors are safe to use as long as it’s 12°F or higher outside. You can go lower if you’re using a special low-temp product with a tackier adhesive.
All products come with manufacturer guidelines to ideal day-of conditions. A distributor with technical expertise can also answer any concerns leading up to the installation.
By spending a little extra time prepping the sheathing base now, you’ll help the barrier adhere and seal against the surface much, much later.
Many sheet products require a primer or adhesive to make the bond stronger. Primers are doubly important when the sheathing surface is porous, dusty, or otherwise tricky to bond to.
Whether you use a primer or not, the substrate isn’t ready for installation until it’s:
It doesn’t have to look like silk curtains, but the working surface must be at least somewhat smooth for the primer and barrier to stick. This may require sanding or other treatments to eliminate sharp edges and mortar droppings.
Accurately measure the space where the barrier will be installed. Sheathing of any kind should have:
When you’re certain you’re ready, cut the material to size. Use appropriate techniques to cut the material without damaging it, keeping in mind the material type and thickness. Allow for some overlap at the seams to ensure a continuous barrier.
If your detail sheets aren’t preformed, you’ll need to cut them now too.
If your primer is dry, or you used no primer, it’s time to address the air barrier itself.
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Primer cure time depends on the weather and the product itself. The best way to determine if you can start applying is to place a (preferably gloved) hand on the primer. Pull it away, and see if any material ended up on the glove. If it hasn’t, then the primer is ready to accept the membrane. |
Starting from the bottom of the substrate ensures that overlapping layers shed water correctly and prevent moisture from trapping between layers or penetrating the barrier.
Sheet barrier installation requires roll pressing the product into place. If not, “fishmouthing” (poor adhesion) and unwanted overlaps might occur. Apply the lowest sheets first, working your way up the wall or across the floor. Set each piece over the one below it to create proper drainage and prevent water intrusion.
Securing the sheet barrier to the structure is essential to performance and service life as the product itself.
Think it through. The alignment and spacing of materials will determine whether they work correctly and merge seamlessly with other building components.
For sheet-applied barriers, the fastening method depends on the specific product. On the cheaper end, It could be:
A higher-quality product is almost always self-adhering.
Use the attachment method the barrier manufacturer recommends. Fasteners should be flush with the sheathing. Cover the fasteners with tape or sealant to keep the barrier fully intact.
As you install the air barriers:
Don’t stop rolling until every square inch of the sheet is on the surface!
Proper sealing at this stage keeps the integrity of the air barrier intact – otherwise, what’s the point?
Contractors attach sheathing to the framework first to give the air barrier a solid and continuous home. If the installation is vertical, make sure that neighboring sheets are lapped tightly as you place them on the sheathing.
Naturally, you’ll be looking at seams and penetrations as potential trouble sites:
Any area you fail to secure could create an opening for moisture and air to rush in.
You’re not ready to hit the Wendy’s drive-thru just yet. Before you say “mission accomplished,” closely inspect the sheet air barrier.
Check for any:
Use the appropriate tape or sealant to make repairs immediately.
Note the emphasis on “immediately” – swift action is key to maintaining the barrier’s effectiveness. Regular inspections during construction and after any significant repairs to the building envelope will help your work last longer.
Sheet-applied air and vapor barriers take a little extra work and diligence, but in many commercial construction projects, they’re worth it. Plan ahead, take your time, and check your work – it’s better to nail it now than hear from an angry property owner later.
If product installation is still tripping you up, seek out the manufacturer or distributor. We offer a suite of training services for contractors working with a new material or project type: