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Installing a Nail-Fin Window Over Zip System Sheathing

This tutorial will show you how to install a flange window in a wall that already has zip system sheathing. The goal is to connect the WRB of the wall to the WRB of the window, making one continuous environmental separator.

Creating the Opening for a Nail Fin Window

This tutorial will show you how to install a flange window in a wall that already has zip system sheathing. The goal is to connect the WRB of the wall to the WRB of the window, making one continuous environmental separator.

First, you will prep the sill pan below the window. You will start by babbling the sill. There is two different ways that you can do that.

  1. Use a piece of cedar beveled siding, creating a positive slope to the outside
  2. Add a 5-degree pitch to the outside in the rough framing sill, creating a positive slope to the outside in the event there is ever moisture

Take a couple roofing nails to tack it into place and hold it for the moment. Once the sill is installed, utilize the stretch tape. The contractor in the video starts with a centerline layout, and layouts up each jamb to the point that he needs the tape to go. That way he does not make any mistakes on placing his tape.

Mark the center on the sill and six inches up each side. Going six inches up each side gives you enough space to turn the corner and a good point of reference, so you are not trying to push a small piece of tape around the corner. You want it high enough to get good adhesion.

Moving on to sill pan flashing. There are a couple of different ways you can do this.

A. Stretch Tape (Preferred Method) - Use a stretchable tape that will flash from the sill out and onto the wall. This will allow you to turn the corner up both sides so that you are able to go from the layout line down, around, and back up to the layout line in one piece.

    1. You have a layout line on the center and have a centerline layout on the tape. That centerline means that you will end up with the same amount after you try to turn the corners. Peel the tape one side at a time. This can be a little unwieldy to do by yourself, especially on a larger window. Peel the tape back and all the way down, trying to keep it from sticking to itself or anything else. Now, you will start on that centerline most of the way back in the opening, giving you the ability to lay at each direction. Tack it temporarily, then work your way back this direction before making the turn. Use a speed square to push it right into the corner so that you know it’s not rounded. Push up once you are at this point. You should be able to turn starting at the corner, working your way out. You may see it start to try to return to its original position, but once you give it a little bit of pressure it'll stay where you want it. You want it to be able to shed water from the sill out and down. Now, do the same thing in the other corner. Once the tape is down and where you want it, start rolling it, then wet the surface.
    2. After your sill is installed and rolled in place, you will work on the vertical. Push the vertical seam/vertical connection from the WRB on the wall to the inside and connect it to the rough framing. This will prevent any error water moving in between the connection of these two things. Use the seam tape to accomplish this task. On the vertical, still overlap everything below it. We will be concerned with any seams on the head and will cover them when we get there. Start by putting down layout marks. Measure two inches out and keep in mind that the tape is three and three quarters wide. You will also need to add a small reference mark at the top as a point for when you start this tape and that run to come down. You do not want the tape to go beyond that two-inch mark. Continue and mark both sides. You will now be ready for the tape. Do not pre-cut the tape because it does not have a backing on it. Get in the habit of rolling each piece of tape before you move on to the next one. Make a small slice to fold in and a small slice at the top to fold in. Press everything in place with your hand first because if you don't the tape could actually shift a little. Start in the middle and work your way out. It's not a major concern if the stretch tape or your sill pan tape protrudes past the sides because they're still overlapping the correct direction. Fold the tape in. Everything should get some hand pressure to make sure that it is seated in the place that you want it before rolling it. Pressure sensitive tape will not stick long-term if you don't allow it to grab by actually rolling it. You don't want to use your hand as the roller because you won't get even pressure. Now that you have your jams installed, you will address the head flashing.
    3. The tape they use in the video is not required by most window manufacturers, Pella, or to get your warranty from the makers of the zip system sheathing. However, if you are sealing from the sheathing down to the jamb it accomplishes the same thing that you have done on the sides (stops an air leakage at that framing). Put your line across the layout line for the tape so that it can be nice neat and straight. That layout line will also give you a reference for where you should cut the tape off because you will want the tape to come down and lap over it in the end. So, you should cut that off or peel it back, giving it the ability for everything to shingle into place. So again, you will start with the layout marks, take your knife and go up roughly a quarter of an inch. That will give you plenty of room to get the tape in there, roll it, and when you add another piece at the end, covering over that. You will need to do one more step before the head flashing tape. Address the joint between the header and hack studs. Simply put a piece of tape that turns the corner. That tape will run lengthwise through the opening. Lightly tack the tape to something to make it easier to cut. Once a piece is cut, tuck it into the corner, slowly work it in so that it's straight, use your hand again to make sure you like where it's touching, then repeat on the other side. Roll the pieces out before moving to head flashing. This will limit the ability of air inside the opening in the corner to migrate out and in between jack and king studs. Allow the last piece of tape to fly a little past your vertical jams on each side, ensuring that you are covering fully. It also gives the ability to make your cut away from that piece of tape. Press it in place with your hand, make the vertical cuts, then fold it inward. While pressing it in place with your hand, make sure that you limit the amount of air bubbles that you are trapping inside of it or just poor placement. Roll it in place and you will be ready to unpack the window.

    B. Straight Tape - If you do not have the stretch tape, using a straight tape will allow you to achieve the same thing. You will have to use more pieces of tape for this method. How this works:

      1. First cut a bowtie shape piece of the flashing tape. That will be your piece that bridges the connection from the sill to the wall, flashing the pan. *Side note: The contractor in the video uses the Hueber Family products. It is recommended to stick with one manufacturer throughout the process, so you only have one rep or one warranty to go through if you ever have an issue.
      2. The second step is cutting a V or a triangle out of both sides of the six-inch piece of tape. Once you make the cut, apply the tape so that when you turn the corner a lot of that material is gone. This will take care of what would have been a pinhole gap. Put a vertical piece of tape over the piece you just placed in the corner making a cut so it can fold in over the edge. The three pieces of tape you put in place will manage the water at the edge.
      3. Take one more run of the tape in the back of the sill to protect it as far back as you can.
      4. Roll the whole system into place with a pressure-sensitive adhesive. You need pressure to make it adhere to the substrate.

      Placing the Window

      Now that the rough opening is flashed, it is time to install the window. The first step is adding shims to the sill. The sill in the video has sloped cedar, so they use other pieces of that sloped cedar and turn them around the other direction. That is going to do two things. First, it is going to create a level platform for the window to sit on, supporting the jamb coming down. It is also going to help center the window in the opening. Centering the window in the opening is the best way to get equal insulation or air sealing around the interior side. After those cedar shims are sitting in place, check them with the level to make sure that you like their location. Make sure the windows will sit level in the opening. If you need to make any adjustments, place shims underneath or on top of the pieces of cedar. Once you are happy with their placement, use a couple pieces of the leftover tape and tack those in place so that they do not shift. Once you are done sliding the window into place from the outside and have the second shim in place, you are ready to prep the window.

      In the video, the contractor folds the nailing fin up. There are a couple different ways that a fin might ship to you:

      1. Already in a 90 degree orientation
      2. Integrated, but needing to be folded
      3. Shipped separately depending on the size of the window or patio door, that way you would see it in a bead of sealing

      Resting it on a couple stacks of two by fours will allow you to rotate and fold the flange out without having any worries. Pick the window up and do a temporary fit. The reason for this temporary fit is you will want to make sure that the window is going to fit. Get it centered in the opening with the help of an interior carpenter and trace three sides of the opening around the fin. The reason for tracing is it gives a clear point of where you want your sealant to go after you set the window back down. This will allow you to avoid putting your hands in sealant and avoid putting the window in the wrong location. Now, you can set the window down and get your sealant.

      Apply a bead of silicone sealant to both sides in the top of the opening. Do not apply any to the bottom so there is a pathway to the outside if water find its way in. Check to make sure that your sealant is approved by the manufacturer of both the substrate and your window. It is not required by all window manufacturers but is a good belt and suspenders approach. You are ready to place the window.

      Tack the window in two places at the top corners and check if it is level plumb and square. Once you know if the window is level plumb and square, finalize your fastening depending on manufacturer recommendations. It may be every hole, or every other. Check with the manufacturer and the instructions they have provided. The unit in the video is every opening. Now that you have the window securely fastened and it is level plumb and square, move on to final flashing.


      The final flashing for the window involves a few more pieces of tape. Leave the sill open so it is available for drainage. Have a piece of tape on each side and a couple across the head. The contractor in the video will show you how that looks with an integrated flange.

      Make sure the tape turns from the wall and in the flange onto the edge of the window, protecting the joint between the flange and the window. Start by working in small sections, making sure that you are in the location you want on the WRB and the window. You should be pushing it in place with your hand, seating the tape where you want. Do not rely on the placement of the roller to hold the tape where you want. Make a simple cut on top and where the tape transitions from being on the edge of the window to needing to lay. Roll that piece of tape in and get it completely seated before moving on to the next piece of tape. Same thing on the second side. By doing this, you are ensuring that the transition from the WRB to the edge of the window is covered and one continuous surface.

      Now that the sides are flashed, it is time to move on to the head again. This will use a couple pieces of tape. In the video, the contractor has simulated a vertical seam. They will peel that tape back, fold it to the side, and apply one run of tape the same as they did on the sides. This allows them to be flashing from the WRB to the edge of the window, past the flange joint. They will then come back and add a second one that is a little wider and a little higher, allowing it to fold back over the top and everything will shingle as if it were a roof. Take the first run past whatever horizontal you have, that way you are completing the taping a little further out each time in the opposite direction of the verticals. Cut that piece a little bit so that it will lay flat. Continue to work the flat down, onto the top of the window. It should bridge from the WRB, past the nailing fin and on to the edge of the window. Seep the other piece of tape with your hand, the next piece will roll both at the same time. Get a little wider and a little higher with each pass. You can seat that tape one more time and finalize its install with the roller. You will want to make sure to get on both sides of the window. Now you are ready to bring the head flashing tape back down.

      Just like the horizontal it gets rolled in place as well. After that vertical seam is rolled, attached to our head flashing and down our sides, we are completely managed for water. You could add a head flashing and that head flashing would be taped horizontally with the vertical legs sitting over top of it. Now let us go inside and talk about air sealing.

      Air-Seal and Insulate the Window

      Now that your exterior is watertight, you're going to go inside to deal with air and thermal. Use a spray foam application around the perimeter of the window. This method will apply no matter what your WRB is on the outside. The goal is not to completely fill the void, but to fill the first inch or so from your side towards the outside. It leaves an open area on the outside of the window so that if you ever have any moisture in that assembly it can migrate out. Take special care to be using the correct foam in the assembly. The contractor in the video uses a formulation made for windows and doors which means it will not cause the jams to bow or bind in any way. Once your foam is installed, let it dry. Trim back any that needs to be cut away and then you have one more air ceiling detail.

      After giving the foam a few moments to skin over, apply a sealant over any shim that will bridge from foam across the shim and back to the foam making one continuous air seal. With those last beads of sealing in place, the interior and exterior are detailed and you can be confident that this will be a leak-free installation.

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