Last month, Coastal Connection stopped by a Roxbury, Mass., jobsite under construction by the innovative Boston firm PlaceTailor, where we got a look at an interesting solution to providing drainable, breathable strapping under the siding in a rain-screen wall assembly ( "Easy, Low-Cost, Drainable Strapping for Rainscreen Siding," July 22).
Last week, the European-made Schuco super-windows for the Passive House project arrived, and it was "all hands on deck" for a day while the project managers and crews came together on site to install 27 windows in three hours, says company Strategic Director and co-owner, Declan Keefe. "We have it down to where two people can set a window in about 20 minutes," says production manager and company co-owner, Evan Smith.
The design calls for the windows to sit flush to the outside sheathing of the drainable wall assembly. A system of bolts through the jamb makes setting the tilt-and-turn windows a simple operation: The crew screws temporary rails across the opening to keep the window from falling out; sets the window in place; screws temporary blocks to the inside buck jambs to hold the window steady; then opens the window to plumb and level the unit and set the supplied self-tapping lag bolts (see slideshow).
A set of framed window openings in the northwest corner of the two-family in-fill building in Roxbury, Massachusetts. Walls are 16-inch–deep, double-stud construction, with inner and outer walls joined with plywood gussets. Exterior sheathing and window bucks are ZIP System structural panels.
Window labels call out the different solar gain characteristics and heat emission values for the window glazings used for different wall orientations and solar exposures. Higher solar gain windows are placed on the south side, while the east and west windows are chosen for reduced heat loss.
A crew member tapes the exterior window edge to the wall sheathing after the window is placed.
The bolted connection also makes sealing the windows into the wall relatively simple: The crew tapes the outside edge of the window to the wall sheathing, fills the gap between the window and the framing bucks with expanding foam insulation sealant, trims the sealant flush on the inside and tapes the inside edge to the window buck.
The building, set on a heavily-shaded urban-infill lot in a wooded section of Roxbury, has limited solar exposure. It's also a two-family design (the lower unit has the entire ground floor and half of the second floor, while the upper unit gets half the second floor and all of the third floor). To make this design work, the building needs windows on all sides—the option of placing most of the glazing on the south side, typical in U.S. northern climate Passive Houses, wasn't practical. But Smith says that by selecting window glazing carefully, the designers were able to hit the required heating and cooling demand for the building (walls are 16-inch-deep double-stud frames, insulated with dense-blown cellulose). The south-facing windows on the street side of the house have a higher solar heat gain coefficient than the east-, west-, and north-facing windows. But this also means that the non-southern glazing has a lower center-of-glass U-value, making for a warmer wall during the heating season. Overall, says Smith, the windows provide the equivalent of an R-9 or R-11 wall in the glazed area of the building.