My Cape-Window Installation

It’s been a while since I last posted about my home.  Exterior work continues…north and west siding is complete and I’ve started work on the back yard or east side of the home which requires removal of a deck and sliding patio door, replace three windows, installing the water resistive barrier (WRB) with rain screen and re-side.  I am also planning on extending the roof eave to move the rain drip line further from the foundation.  More than enough weekend work for the summer.  First pic was taken right before I purchased the home.

There are three different siding types on this side of the home.  The original asbestos lap siding, from 1952 is on the second story dormer sides, a wood batten and board type around the back entry door, which I believe was installed around 2000, and vinyl siding which was installed around 2017.  I removed the sliding patio door late last fall so I could finish the master bedroom closet.

The windows were delayed a couple weeks so I installed the Henry Blueskin around the old window units with the plan to cut the Blueskin and replace pieces when the new windows arrived.   I’m not replacing the door, it’s in good enough shape but will eventually add a new storm door.

The subject of this post is the challenge of installing a new window when using both a self-adhered WRB and vented rain screen.  The home is sheathed with board sheathing, which is the one of the reasons I had such a poor blower door test, around 12 ACH50.  I am hoping to greatly increase the home’s comfort and efficiency.  Air sealing is a big part of the master plan and sealing all the gaps and cracks from the board sheathing is one of the steps.

The self adhered Blueskin will seal the face of the board sheathing, but where the boards are cut for the window openings, there’s the potential for lots of air movement.  Normally I would just extend the Blueskin membrane into the window jamb rough framing.  Because of the window delay, the Blueskin was cut around the old window.  Removal of the window left what you see in the picture above.  What I decided to do was add a piece of flashing tape around the sides, top and bottom.  I needed to add a little additional framing to slightly decrease the window rough opening to fit the new window.  I also pitched the sill a few degrees to allow any water that should enter the around the window to drain outwards.

I was given a sample of Siga’s Wigluv which was used for the air sealing.  If you’re not familiar with Wigluv, it’s one of the high quality European tapes being sold in North America, a very impressive tape to work with.  It’s air and water tight but still can allow outward drying if needed.  One of the few tapes available with a perm rating.  After taping the edges and framing joints, I added the 3/8 inch fir strips as window bucks to extend the window plane so it’s even with the vented rain screen fir strips.  I then cut narrow pieces of Blueskin and wrapped over the buck and into the sides of the window opening.

The top of the window will be addressed later.  The bottom was flashed with Henry’s FortiFlash Butyl flexible window flashing.  A product similar to Tyvek’s FlexWrap.

Next was to install the window.  I placed a bead of Henry’s Crystal Clear Sealant around the top and sides of the window opening (not the bottom) and then installed the window as recommended by the manufacturer.

The windows themselves are from a local manufacturer called Walsh Windows, manufactured in Duluth, MN.  These casement windows are made from uPVC or unplasticized-poly vinyl chloride which is an improvement over the older PVC type windows.  I ordered a slightly upgraded window with better performing glass which decreased the window’s U-factor to .26, giving the window a total of R-3.85.  Not great, but better than most code minimum windows being installed which are U-.3 or R-3.33.  Read more about windows here.  Another thing I like about the Walsh Windows is they have a 100% sash replacement, no questions asked.  I installed these windows in a customer’s home several years ago, he later broke a window while mowing lawn.  They sent a new sash free of charge.  How many window companies offer that?

The next step was to install Henry’s butyl flashing tape designed for sealing the window to the Blueskin.  Taping the two sides and head are standard details for most WRB’s.  Never tape the bottom window flange.  This must remain open to allow any water that should leak into the window assembly a place to drain out.

Best practice recommends installing an additional metal head flashing at the top of the window and then wrapping the WRB over the flashing.

This detail becomes more complicated when using a self-adhered WRB.  Henry’s instructions are to install the head flashing before the butyl tape, a bead of the Crystal Clear Sealant would then be applied at the top of the top butyl flashing tape.  I’m not a fan of relying on a caulk or sealant to keep water out of exterior assemblies.  I instead added a second layer of Blueskin over the head flashing and extended the WRB up to the roof eave.

I have heard the saying, “There are two types of windows, one’s that leak and the one’s that will leak.”  I have confidence that this install is in the “will leak” category, hopefully far into the future.

Last pic shows the final prep, installing the remaining 3/8 stripping used for the vented rain screen.  Will have a short post showing the finished East side sometime this fall.

4 Replies to “My Cape-Window Installation”

  1. Nice job on the window install. I like the extra layer of blueskin over the top of the metal head flashing up to the first floor eave. I like this approach for wi Dow heads in fairly close proximity to eaves.

    1. Thank you. I followed Blueskin’s directions on other windows on my home and didn’t feel good about using a sealant over the top of the butylene window tape at the head. Much more confident in this detail.

  2. Great detailing on the window installation. This is critical for long term water resistance. I use DuPont flex wrap for the undersill. It is expensive but a roll does many windows and gives me assurance of building longevity. You rightly point out the sill plate needs to be sloped outward so any water will drain via gravity out and over the WRB. I have been into a lot of walls and removed many old windows and it is the bottom corners and sill that show most of the water leakage to the exterior sheathing. The new WRB’s and flexible flashings put an end to that.

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