We learned a lot about windows…hence this post to pass it on.
First, we priced a number of European windows that would work for our demands: we needed glass at about U=.09, frames at about U=.15, solar heat gain coefficient of .5, and insulating spacers. We learned that the UPVC windows (Intus, Unilux Isostar, Zola) fit the bill at the lowest price. Great prices, actually, as in, competitive with good US wood/clad windows (I recently heard around $34/s.f. for UPVC units). Our clients preferred aluminum clad wood, though, and we wound up choosing Zola’s Thermo line. Their performance was great, and their price beat the competition easily. They’re made in Poland with German Roto hardware. Florian Speier, the architect who founded Zola, helped develop the THERM protocol for determining installation thermal bridge values, so he’s a good resource to the Passive House Consultant as well. By the way, I’m not going to name “the competition” here, because the pricing we got might not be indicative of where their products stand today, or with other project specifics, and I don’t want to prejudice anyone unfairly.
A few logistical items to note:
– Shipping from Europe didn’t allow for an exact delivery date: plan for flexibility.
– The shipping container was packed excellently for safe travel of the windows, but not for jobsite storage (the windows weren’t individually crated).
|Inside the crate|
– You typically have to pay to hold a shipping container on site, so either unload the windows to a safe location (for us not easy on the small job site) or install them right away.
– These are beautiful, finished, furniture-like pieces of equipment, so they need protection for the duration of construction.
– Powder-coated Zola screens were expensive–we’re going to have them made locally instead.
For installation we had two options: screw through the jambs into the bucks, or use metal clips that slotted into the jambs. Since we had solid concrete behind the jambs, and didn’t have close enough tolerance on all the shim spaces, we chose to use the clips.
|Clip is just below green tape, which is covering buck anchor|
That meant we had another blip to deal with in our airtight layer, but by this time we were so Siga-happy we didn’t worry about it. As you can see, we used the Siga Corvum to tape the jamb to the buck (Corvum is pre-folded with two peel-away strips on the back, made for corner air sealing), and the Wigluv to cover the clip-blips.
|Air sealed window. Note: interior overinsulation will cover tape.|
Initially we were concerned about the airtightness strategy at the windows, but having done it, it’s actually pretty easy and entirely visible and accessible, making it easy to fix if there are any weak points.
The weathertightness on the outside was handled with more traditional flexible flashing. Here’s Brandon Weiss, the GC, explaining how that was done:
And here’s an exterior view, with a window awaiting the overinsulation on which to tape off the flexible sill flashing:
|Exterior: west family room window|
Man, I should offer CEU credits for this blog post! Hope it’s helpful to those out there detailing. Your comments are welcome…this is a learning experience for us.