How to Install an Airtight, Watertight Window with DELTA®
In this post, I want to show you some of the important details for installing DELTA®-VENT SA. I will walk through all the steps of installing the house wrap and then focus on what it takes to flash a window, using the DELTA® line of products from Dörken Systems Inc.
Dörken is a German company that produces this DELTA® wrap. The “VENT” part of the name refers to the fact that it’s vapor permeable (around 50 or 31 perms, depending on which ASTM test method is used to evaluate the material’s permeability). “SA” stands for “self-adhering.” This is a peel-and-stick, but it’s unlike any peel-and-stick that I’ve used before. The material feels almost like a denim cloth, or jeans material – it is very light and allows vapor to drive to the outside.
I love that it’s peel-and-stick on the back, and that at the overlaps, it also has a peel-and-stick on the front, at the edge, so when the two sheets overlap you get a very tight, air-tight bond. That adhesion is vital to me: I am really looking to get as airtight a shell as possible on my projects and that’s the beauty of this material – it’s both a water-resistive barrier and an air barrier.
Why stick-on house wrap? One thing to think about with conventional house wraps that are applied loose over the sheathing and pinned in place with cap fasteners: to get any type of air barrier at all with a loose house wrap, you need to tape the seams. But this only provides limited airtightness. Air moves in both directions through a wall. When the house is depressurized, it pulls the house wrap tight to the sheathing. Or when the wind blows into a wall, of course, it pushes the house wrap tight to the wall and stops air coming in through the seams in the sheathing and all the other gaps the house wrap is covering.
But what about when the house is positively pressurized? Or what’s happening on the leeward side of the home? Well, positive pressure inside a home is pushing out through the gaps in the wall and, in effect, ballooning the house wrap out to let air escape. And wind on the leeward side of a house is creating a negative pressure against that wall that pulls the house wrap away from the wall, and once again this gives air a chance to escape. Over the course of any day or a week or the year, air pressure inside and around the home is constantly fluctuating, pushing and pulling on the wall, bringing air in and pushing air out through any gaps. If you want a reliable air barrier, it makes good sense to stick the house wrap tight to the sheathing.
So here’s how the installation procedure works:
We first use their primer, rolling it right out of the bucket onto our wall sheathing.
The primer we’re using on the project shown in the photos and the video with this post is called DELTA®-ADHESIVE LVC – a rubber-based adhesive that comes in a five-gallon bucket. They also make DELTA®-HF PRIMER, which is water-based and solvent free.
The primer goes on our sheathing, and creates a sticky surface, so once we peel off the backer on the house wrap and apply it, we’ve got sticky on sticky. It forms a very tenacious bond that is going to maintain air tightness. To be clear, the primer isn’t an actual adhesive, but it is great for wall preparation.
Applying the wrap.
We snap a line to align the first course at about 5 feet – the width of a roll of DELTA®-VENT SA – on the wall.
We install the first course, adhering it first along the layout line, holding the material out flat and then smoothing it out to avoid any wrinkles.
We then install the next course up, overlapping this one with the bottom course. Note here we run the house wrap right across the window rough opening, as if the window wasn’t there.
Prepping the window opening.
Once the house wrap is applied, our next step is to cut out the window, creating a 45-degree cut from all four corners towards a vertical center cut.
This gives us flaps that we fold in on all four sides.
An important note here is that our sill has been pre-sloped. We do this at the framing stage. My framers cut a 5-degree angle on the cripples, so the sill goes in at a slope to the outside. Any water that gets past the window is going to roll with gravity towards the outside and drain out.
Flashing the windows.
The first step is to create a sill pan by installing DELTA®-FLASHING on the sill.
This is not a flexible flashing so we need to treat the corners. We do this by making a “dart” with DELTA®-FLASHING to cover the corner.
We apply one more piece of DELTA®-FLASHING to cover the dart, making sure everything is shingled correctly.
Completing the sill pan.
The last step for completing the sill pan is to apply a strip on DELTA®-MULTI-BAND across the top piece of flashing on both sides of the rough opening. This final piece on the sill pan helps ensure complete airtightness.
With the sill complete, the final step to our window install is treating the head. All we need now is DELTA®-MULTI-BAND: We run it on both 45-degree cut corners, along the corner at the top of the window rough opening, and one more piece on the very front, just to make sure everything remains nice and watertight.
At this point the window is ready to install, and we’ll use our standard window install method, beginning with a few horseshoe shims on the sill.
We then run a bead of DELTA®-TILAXX adhesive sealant around the very edges of the opening, so it ends up under the window flange.
We apply the sealant in a U-shape around the sides and the head of the rough opening. We do apply any sealant or adhesive along the bottom edge, as we want any water that gets behind our window to have a chance to drain out at the sill.
Once the window is installed, we then apply DELTA®-FLASHING over the window flanges on the sides and across the head.
Here we are careful to press the flashing tight with a J-roller to ensure good adhesion on all the flange and wall surfaces under the flashing.
Again, we will not flash across the bottom flange so we allow a chance for water to drain out at the sill. (We will rely on a foam sealant applied from the interior to address air sealing here.)
Lastly, we apply a strip of DELTA®-MULTI-BAND across the top of the head flashing just to make sure the very head is totally sealed.
That’s it. Super easy, super water and airtight. These top-quality waterproofing materials that are vapor permeable. They’re going to work in all climates zones. I’m down here in Texas (CZ 2), but these materials would work just as well in a cold region, be it Minnesota (CZ 6 and 7) or Alaska (CZ 7 or 8).
About Matt Risinger, CEO & Chief Builder at Risinger & Co.:
Upon graduating from Grove City College in Pennsylvania with a degree in Industrial Management, Matt began his construction career at NVR in Washington DC.
In 2005 Matt and his growing family relocated to Austin where he started Risinger & Company. Matt is dedicated to Building Science and is a recognized expert & thought leader in the industry.
He also has a large following on his YouTube channel, where you can find videos on installation techniques, product reviews, and everything in between. You can find additional details on Matt on our About the Blog page.