Double-Stud Walls

Basement windows
by Martin Holladay, GBA Advisor

David,
If your basement windows are "partially above grade" and partially below grade, the exterior of your basement walls cannot be insulated with Larsen trusses, since Larsen trusses include wood components that shouldn't be used below grade.

I recommend that you transition to a different method of exterior insulation for the below-grade portions of your walls. Most builders use XPS foam to insulate the exterior of basement walls. The above-grade portions of the the XPS need to be protected from damage by UV light and weed-whackers with cement backerboard, fiber-cement siding panels, pressure-treated plywood, metal flashing, stucco, or proprietary plastic panels.

Basement windows with Larsen truss retrofit
by David Argilla

How do you detail basement windows with a Larsen truss retrofit. We need to remove siding on our house, so Larsen truss looks interesting for insulation retrofit. I can see how to deal with above ground windows, but how do you incorporate basement windows that are partially above grade?

Excellent suggestions
by Martin Holladay, GBA Advisor

Jamie,
Thanks for your excellent suggestions. We'll do our best to address these questions in the months ahead. Stay tuned.

...and the openings?
by Jamie Wolf

Martin has covered the innie-outie debate regarding placement of windows in thick walls. I find thinking about the opening details - including doors - related to these important decisions to be an often glossed over part of this discussion. The wall section alone is the easy part. I'd love to see a series on thick walls and roofs that digs into the harder parts, i.e. the openings with flashings in three dimensions, the foundation/floor/ceiling/roof interfaces, the thermal bridge issues, and maintaining the continuity of air, vapor, weather, and thermal boundaries in all of the above.

... oh, and doing all of the above durably, simply and efficiently with as little foam as possible!

Translation
by Anonymous

translate.google.com did an acceptable job of translating the german PDF. Thanks!

The document is no longer on line
by Martin Holladay, GBA Advisor

TrusJoist Macmillan developed engineering details for using their TJIs as joists; however, the method was promoted only in Germany. The German document containing the necessary details had a curious title: "Balloon und Platform Framing Details" — with all of the title's words in English except "und."

When I wrote an article that referenced the document for the May 2004 issue of Energy Design Update, the German document was posted online. It has since been taken off-line.

Fortunately the document can still be accessed through the miracle of the Wayback machine. Try this link:
http://web.archive.org/web/20051111012117/http://www.trusjoist.com/PDFFi...

Of course, to read the document, it helps to be fluent in German. I'm not.

TJI as studs
by Anonymous

"The manufacturer of the I-joists that Sindelar used, Trus Joist/Weyerhaeuser, has developed details allowing their TJI floor joists to be used as studs."

Can you point to a source for this? A link in one of the PDF files at the Passive House US site detailing the use of TJI's as studs is no longer functioning. A search of ILevel.com site turned up nothing as well.

double wall double plate
by Robert Swinburne

I have done a number of double wall houses. my preferred method is to frame the house as a normal 2 x 4 exterior wall house then space what is basically an interior wall 1 1 /2 or 3 1/2" inside the exterior wall. stud alignment is for sheetrock and only has to line up at windows and doors. It helps to think of it as just another interior wall. Flash and batt (spray 1" to 2" foam then cellulose) works very well for this system.

Double framed walls vs. SIPS
by Michael Shubat

Great idea for using a 'standard' process to increase U-values, but I have to disagree on the cost comparison to SIPS. In particular when the cost of insulation is factored in, I have found 6" SIPS panels to be barely more than single wall 2x6 with batts. The labor savings of SIPS in the framing and sheathing stages (remember, every wall is framed AND sheathed when you stand it up...) combined with the low thermal bridging and 'super insulating' qualities inherent in SIPS easily offsets the tried and true balloon framed shell.