How To Install Nail Fin Windows Over Rigid Foam Insulation

In this studio mock-up we're gonna install a flange window in a wall with exterior insulation. When you get to the project this foam actually won't be in place. What we have here is two inches of foam and a buck so that you can see where we're gonna wind up, however the starting point of this assembly is we're gonna waterproof from the substrate behind the foam around the buck and to the inside creating a weather tight at window installation. Now that we have the foam moved away you can see that we're gonna be utilizing the zip system sheathing is our WRB in this assembly that means that we're going to need to connect this WRP to the inside of our opening. There's a couple different ways that we can do that. One, we could use their stretch tape we could use their straight tape with a bow tie in the corners but in this instance I find it way easier to use the liquid flash to make all these transitions turns and connections in one piece. My liquid flash application starts with a few layout lines around the buck, that way I can ensure that I'm getting solid coverage all the way around. I'm gonna make three passes on the outside of each unit and then I'm gonna spread that to make sure that I have even coverage. I'm going to try to push my spreader into the opening where I'm really sharing it with that corner. I'm sharing it with that joint but I'm also trying to cover both the WRB and the and the framing but at the same time I'm not trying to jam it into the corner where I have a square corner. I'll have enough room around my insulation that I can handle making the transition from the framing buck to the WRV without it having to be really struck hard in the corner. The entire purpose of everything that we're doing here is to make one connection from the WRB of the zip sheathing down and into the opening. So we want to take special care when we're turning corners. We want to take special care when we're moving between different types of material or between different sections of the material. You don't have to worry about getting it in one pass the cure time for this liquid flash is somewhere between 20 and 40 minutes depending on temperature, so you have plenty of time to to work the product into place. The liquid flash is a moisture cure product so temperature's going to affect it but humidity will also affect it so if you're working low temperatures with low humidity it's going to take longer to set up. If you're working on a hot day with high humidity it's going to set up quicker, so you can see that our liquid flash is actually bridging across our horizontal tape seam. We have to be careful here this tape is shipped without a backing which means that this tape has a release agent on this side to keep the outer run of tape and the roll from sticking to it so we've taken acetone and wipe down the face of the tape there just so that we're sure that we get adhesion from our liquid flash to our tape. So there's a couple reasons that I started at the head and then worked one side. I'll move to the other side next and finish down here. the reason is this is kind of like painting I don't want this product to skin over so if I were to start say at this bottom right hand corner and work my way around I would be ending at the place that I started. It's more likely to have skin on it or starting to cure at that point then it would be if I start at the top work down and then do the bottom. Now that we have our sides and our head flashed we're going to add a piece of cedar bubble siding to the sill that will give us a positive slope to the outside in the event that we ever have a moisture. So when I'm working on this bottom sill I would rather start at the bottom and work my way around. That way even if I'm dragging horizontally if I need to turn the corner I can be pulling the material uphill rather than trying to drag downhill and cause drips. [Music] Now we're detailed to the backside of that cedar bevel siding we don't have to go beyond because we won't have water getting that far back and that cedar extends beyond where the inside of the window will actually be. We're ready to let this skin over and then install our window.

Now that our jam and our buck are both waterproof of the liquid flash we're able to add a couple shims one on each side. These are just a piece of that cedar bubble siding that we were using before we'll put them in the reverse orientation of the piece below them creating a level plane for our jams to sit on, on each end. As you can see we're standing the last of these nailing fins up. There are a couple different ways that you'll get a flange window. One they might be integrated like this but fold it over for shipping purposes. Two they might already be in this 90 degree orientation or three they might be separate and you'll be responsible for beating it in silicone and then tapping it in place. Now that we have all the fins up we're ready to test fit the window. The first time now that we have the windows sitting in place temporarily will have a carpenter on the inside of the building help us. Center it in the opening that'll help us maintain our insulation line all the way around. I'm gonna take a red or a silver permanent marker and I'm gonna draw a line around that flange so that once we set this unit back out I have reference for where I want to run my bead of sealant behind the flange. Now that we have that reference line from where our flange will sit at final installation we're gonna lay out a bead of the liquid flash behind the flange. It's not required by all manufacturers but it will give us a belt-and-suspenders approach because we'll seal all over top of that flange after the window is installed. Now we've placed our window in the same position using the reference marks that we made earlier we'll tack it in a couple places and check it for level plumb and square. Now that we know the unit is level plumb and square we're able to go ahead and fasten the fin or the nailing flange. The only thing that's different on this assembly is we're not gonna be using a tape here and since we're using this liquid flash that has a slight tack to it we're gonna put a couple of horseshoe shims underneath the bottom flange that'll keep it from sticking. It'll give it a clear path for any water that might find its way in to migrate out. I like the horseshoe shims because they'll hang on the fastener when I go to put it through the supplied opening but the other thing is this is a synthetic shim so we don't have to worry about this shim swelling due to water like say a cedar shim. Then we'll fasten every bassinger hole. You want to check with your window manufacturer on each window type some of them it's not every hole some of them add something different but they'll have a prescribed method.

Before we install the last layer of liquid flash we're gonna take the time to mask off the side of the window. This liquid flash is actually going to roll past where the fin connects and onto the main substrate of the window. So we want to protect that from being covered in black liquid flash at final installation. So we're doing this sealing process in two beads I add a little bit more in the squiggly shaped pattern on the fin than I do on the edge of the window because I need a little bit more material for that bridge but all of this is literally connecting the side of the window frame back out to in our original framing buck. I'm going to take special care to make sure that I really do cover everything and this time I'm okay with wiping a little bit more out of the corner because it's more about the connection between the silver flange and the color of the window. Now we can call our exterior water management of this window complete. The only thing that's left is removing our tape. I like to wait until the liquid flash is dry that way I don't risk any of it being on the tape and getting it on the glass or the window but at this point we're ready to bring our foam in. Now we'll take our seam tape and we'll just detail out our seams. We're gonna leave the top open in case any water ever migrates in above our window. We want a place for it to get out same at the bottom. If we get anything in we want a place to get out. Now that we have our masking tape removed this would be the time to add a head flashing. If you wanted for the purposes of this mock-up we're not going to do that but let's go inside and talk about how we manage for thermal and air.

Now that our exterior is watertight we're inside and we're gonna deal with air and thermal. We're gonna do that using a spray foam application around the perimeter of the window. This method will actually apply no matter what your WRB is on the outside. Our goal here is not to completely fill the void we're just trying to fill the first inch or so from our side towards the outside. It leaves an open area on the outside of the window that if we ever have any moisture in that assembly it's able to migrate out. We're taking special care to be using the correct foam in this assembly. This is a formulation made for windows and doors which means it's not going to cause our jams to bow or bind in any way. Now that our foams installed we'll let it dry trim back any that needs to be cut away and then we have one more air ceiling detail. Now that we've given the foam a few moments to skin over we can apply a sealant over any shim that we have that will bridge from foam across the shim and back to the foam making one continuous air seal. [Music] But those last beads is sealing in place the interior is detailed the exterior is detailed and we're confident that this is going to be a leak-free installation.