window installation details

i know, the title of this post will attract lots of new followers!  in spite of this seemingly mundane topic, it is of vital importance to the performance of the building envelope.  windows are great.  they provide natural light and air.  windows provide a connection to the outside and are critical to human comfort and enjoyment.  windows can also be bad.  inadequately constructed windows can admit unwanted cold air and allow the loss of costly conditioned interior air.  a window can also leak water which can lead to unsightly water stains or decay/rot.  so, we must be careful when designing, detailing and installing windows.  the following documents the chosen window installation at 363:

typical window rough-in

this view shows the basic window rough-in.  the components include the window, Vycor tape (the black stuff at the perimeter of the opening), sub-sill (the black plastic thing at the bottom of the window), and the strip of house wrap (the mostly white paper thing at the bottom of the opening).  the components are layered top to bottom to provide positive drainage.  eventually, the entire wall surface will receive house wrap which will be the drainage plane – it will shed any bulk water that finds its way behind the siding.  then, 1×3 wood strapping will be applied over the house wrap to provide a rain screen behind the clapboard siding.  all of these layers provide durability by shedding unwanted water.  a future post will detail the rain screen components.

bottom corner detail

close-up showing the layering of the various components listed above. the black “GRACE” tape is the Vycor.  its doing two things in this application – one, providing primary weather (water) seal and, two, providing air barrier.  the piece on the “outside” corner (not next to window) is primarily an air barrier.  the SIPs opening has a 2×12 “buck”.  i’m concerned that this field marriage of dimensional lumber to SIPs cut-out will not be a perfect union (even with the two beads of sealant applied under the 2×12).  so, this “extra” piece of Vycor tape is cheap insurance against air leakage.  also note the black plastic sub-sill. it has sloped horizontal sections to provide positive drainage should any water find its way there.  this product is SillGuard, formerly manufactured by Marvin Windows and Doors.  “formerly” because i just learned that Marvin no longer is making this product.  we were able to buy out some remaining stock from EBS in camden. too bad as i have found this product to be a good sub-sill solution.  i guess the next project i’ll have to resort to site-built sub-sill.

interior bottom corner

now, we jump to the inside.  here you can see the 2×12 buck inset into the SIPs cut-out.  the metal clip is screwed to the side of the window and into the 2×12.  three clips per side and two at the top provide a secure window installation.  the gap between the side of the wood window frame and the 2×12 will be filled with spray foam insulation for thermal and air barrier.  the gray caulk at the bottom of the wood window frame reinforces the bed of caulk under the window frame – again, thermal and air barrier.

just in case you haven’t figured it out yet, ITS ALL ABOUT THERMAL AND AIR BARRIERS!  oh yeah, and water (bulk and vapor), too.  remember, we must negate those bad things listed in the first paragraph so the occupants can experience unfettered comfort and enjoyment of their beautiful windows!

4 thoughts on “window installation details

  1. Great post, John. Have you explored tapes? We’ve only really used them once but are super-curious, especially with the euro windows.

    • hi phil, thanks for the thoughtful question. not sure i can say i have explored tapes, as in a “deep-sea exploration”! my experience with tapes is more akin to an “excursion”, as in snorkeling perhaps?! my previous experience with Vycor has been mixed, as it has been on this job. where the Vycor is applied to “real” wood (not OSB) it presents satisfactory results. adhesion to OSB can be a different story. we have had some adhesion failures at the head air-barrier tape, esp. with the recent cooler temps. at those locations, we have replaced with 3M All Weather Flashing Tape – definitely “stickier” but, IMO, lacks the robustness of Vycor’s bituthene-ness. further to the tape-front, the SIPs tape applied to the interior joints is great – it has that robust bithutene quality i like and it really STICKS. but, its not rated for exterior application. nonetheless, we are applying to exterior SIPs joints as a “belt and suspenders” air barrier approach. well, that’s probably enough “tape-talk” for this forum. hope this helps! jpg

    • hi bill. yes, houeswrap/Typar will be applied as the weather barrier/drainage plane. a forthcoming post will detail the rainscreen – basically, an air space behind the siding to promote drainage/drying. jpg.

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