Windows and doors are inherently the weakest link in our buildings' enclosures. Even with the use of great triple pane glass, super-spacers and thermally broken frames, you would be hard-pressed to get an effective R-value higher than 8 (or a Uw below 0.7W/m2k). The good thing about glass is that it is airtight. While the frame portion of a Passive House window is weaker, most frames employ multiple air sealing gaskets as well as multi-point locking mechanisms to ensure tight closure and get you to your airtight goals. (Yes, tilt hinges cause small residual leaks, but these are so small that your 0.6ACH50 shouldn't be compromised).

Retrofit window installation detail. INTELLO making an airtight connection with TESCON Profil and Vana tape to the window frame.

But what's the use of specifying a high performance window if it's installed poorly? A poor installation alone can reduce the window's performance by as much as 25%. Therefore tight insulation around the frame edges and special attention focused on the air tight connection between the frame and the building envelope is a must.

In this example, the INTELLO Plus membrane is used on the interior face of the framed wall. There are two ways of transitioning the interior INTELLO membrane to the window frame in a verifiable and airtight manner. In this case we use a brick/brownstone rowhouse retrofit as an example, but the same approach works in new or existing wood-frame construction:

1. Strips cut to the window box depth

3d exploded view of INTELLO strips mounted from interior airtight layer to window frame

Strips of the INTELLO membrane, cut to the size of the depth of the recess of the window frame, are used to connect the airtight layer to the frame. TESCON Profil tape is applied at membrane overlaps in corners, releasing the strips for a 50-50 width distribution. TESCON Profil is also used to tape the membrane to the interior face of the frame, applying the narrow strip of the tape to the frame first, followed by the remaining strips that connect to the membrane.

TESCON Profil showing the 3 release stips (narrow on right for frame application - or wide papers (1 left, 2 right) for equal corner application)

After the window frame is taped to the INTELLO along all sides, terminate the Profil tape as close to the corners as practical. Then make "pre-made" corners to assure the corner connections are 100% airtight. This corner technique is explained in detail in this blogpost.

2. Membrane cut and folded toward the frame and patched in the corner

Step 1 - INTELLO is run over the window opening first. The membrane is then cut at 45 degree angles from each corner:

1 - INTELLO is run over window opening - it is cut from corners at 45 degree angle

Step 2 - INTELLO is folded inward and trimmed just shy of the window frame, then stapled in place:

2 - INTELLO is folded inward and secured with staple close to the frame

Step 3 - Corner patches (made with INTELLO scraps) are then taped into the corners to assure full and airtight coverage:

3 -Corner patches made from membrane scraps are placed in the corners and taped on all sides.

After the window frame is taped to the INTELLO along all sides (ending the Profil tape as close to the corner as possible), use "pre-made" corners to assure the corner connections are 100% airtight. Video for window installation

(video by Pro Clima partner in Ireland & UK - Ecological building systems).

Exterior

Pressing down TESCON Profil with PRESSFIX on exterior for weather seal and wind-tight connection.

Depending on the location of your window in relationship to the exterior brick, it is also recommended to make a weather- and wind-tight connection between the window and the brick. This can be made using Pro Clima's TESCON primer RP on the brick and then face taping the window with TESCON Profil.

Finishing

Both on the interior and exterior, the tape will be covered with sheetrock or a brick-mold. With it's split release paper, TESCON Profil tape lets you quickly and easily apply the tape deep into the corners - making sure that any finishes won't interfere with the tape. It also assures that the tape will only be applied to the parts of the frame that will be covered by a finish.

A word of caution: it is very hard to remove the tape after it has been applied and pressurized. If you make a mistake or wish to re-align a portion, resetting the tape is possible for a few seconds.

With the window fully connected at the interior and exterior, the window installation becomes a fully integrated element of the airtight layer.