Weather Resistant Barriers Part 2: Window Install Best Practices
"When it comes to installing windows, it's important to develop and execute a system of best practices—it is critically important that you install your windows correctly"
I have been on this planet long enough now to understand there are some things that really need to be done correctly, and at the same time, we may not do them often enough to fully commit them to memory. In the building materials business, selling a skylight comes to mind. Depending on the brand and functionality, it can be a fairly involved process. And if you don’t do it very frequently, it is easy to forget some of the details and make an error.
When it comes to remodeling, installing windows falls into that category (for me). Most of the time, I am smart enough to review my trusted resources before I go to the job—but on occasion I don’t for some reason, and sometimes I pay the price. For a variety of reasons, it is important to develop and execute a system of best practices. On some projects, you can get away with missing a step or making an error. But for those high-exposure situations, it is critically important that you install your windows correctly.
Use a total system
As far as WRB (weather-resistant barrier) systems go, there are multiple ways to accomplish the task these days, ranging from black paper to fluid applied systems. Like many things in life, it can help to create a go-to system for how you install windows on your projects—the key word here being “system,” meaning a system of products from one manufacturer that are designed to be compatible. Using a system designed by a single reputable manufacturer will increase your likelihood of desired performance and also provide you with a warranty and a single point of contact should you ever face a challenge with the products.
Consider a drainage wrap
In a perfect world, we would all be installing a true rainscreen system on every project, but that isn’t always an option. Instead of defaulting to a traditional homewrap, I would encourage you to upgrade to a “drainscreen” product. Drainscreen products are manufactured to help excess moisture find its way down the wall and escape out the bottom. The product Tyvek makes (DrainWrap) looks “crinkled”—as one author put it, “It looks like it needs ironing.” They have a 9’ roll, but I tend to buy their 5’ roll (StuccoWrap) as I find it is easier to work with if I am alone on the job.
Think about air sealing
The concept of air sealing has become much more prevalent in recent years, primarily due to the bang for the buck. Spending a few thousand dollars in this area can sometimes deliver energy savings on par with a window replacement project. For WRB systems, there are a few things you can/should do to help in this area.
- Seal the top edge of the wrap where it meets the top of the wall. I have been taping this edge, but the latest best practice is using a bead of sealant.
- Seal the edges of the wrap where they roll into window and door openings. I have to credit Rick Arnold’s video for this tip. I like to staple the wrap to the framed opening, cut it halfway back, and then seal it with tape.
- And lastly, tape any vertical seams created due to overlaps, and tape any unintended holes, cuts, or tears that happen during construction.
Use a flexible adhesive flashing
The invention of flexible adhesive flashing has been a game changer when it comes to creating a simple and reliable way to protect the sills of your rough openings. Admittedly, it takes a little getting used to, but the scoring of the release paper on the back allows you to expose a limited section of the adhesive, which helps when placing it on the bottom of your framed opening.
Apply sealant behind the top and side window flanges
Although it can seem like overkill (knowing that you will be using flashing tape and properly layering your drainage wrap), applying sealant behind some of the window flanges is best practice. The big takeaway is to not apply a bead behind the bottom window flange. This goes back to our goal of providing any excess moisture that accumulates in the framed window opening with a way to escape.
Choose a butyl-based flashing tape
There are many flashing tapes on the market these days. The key focus here is compatibility and quality. Once again, utilizing a system within the same product brand goes a long way toward keeping you out of the weeds. One of the things to take a closer look at is the composition of your flashing tape. Asphalt-based flashing tapes can be incompatible with the nail fins/flanges on many window lines. Although rare, this can lead to having a gooey mess drip out onto the face of your cladding. And with this type of challenge, you can imagine the negative impact on your WRB system. Choosing a butyl-based flashing tape can avoid these types of challenges as well as provide better performance (adhesion) before the cladding goes on the wall.
Consider the Construction Instruction app
Wouldn’t it be great to have all this information at your fingertips? Well, now you can! Our good friend Mark LaLiberte and his business partners offer animated video content featuring installation best practices. One of the benefits of this type of education is it helps overcome mistakes that can happen due to language barriers on job sites. The Construction Instruction App allows tradespersons to have access to detailed install content for many commonly-used building products.
As you can see, there are lots of things to think about when installing windows. Window manufacturers don’t like to talk about it, but at some point, windows start to fail and potentially leak. The goal of installing your windows properly is to make sure that when they do start leaking, the moisture is channeled away from the window opening and never has an opportunity to enter the wall cavity.
