©2013 Green Building Advisor. From The Taunton Press, Inc., publisher of Fine Homebuilding Magazine.
[Editor's note: Roger and Lynn Normand are building a Passivhaus in Maine. This is the tenth article in a series that will follow their project from planning through construction.]
Enough suspense on windows.
It’s a Bieber ! And yes, that’s our final decision. We’ve made a sizable cash deposit and started precise shop drawings for the windows.
It had been a tortuous four, yes, four long months working with the local Unilux window retailer, Hancock Lumber, to get the right configuration of these German manufactured windows to meet our performance requirements. And that was only to specify the windows.
In defense of Hancock Lumber, this was a new line of windows recently added to their more traditional line of Andersen and Eagle windows. And there was certainly a learning curve on our part, particularly regarding the importance of high Solar Heat Gain Coefficient(SHGC) The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. glazingWhen referring to windows or doors, the transparent or translucent layer that transmits light. High-performance glazing may include multiple layers of glass or plastic, low-e coatings, and low-conductivity gas fill. – a high SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. enhances the interior heat gain we need in winter to meet the Passivhaus standard.
Still, the Hancock window team never seemed to grasp our need, and how the Unilux windows could best fit that need. Would matters improve after ordering, through preparing shop drawings, shipping, importing, customs, delivery, install, and any potential warranty issues? We lost confidence in the product and the distributor last October and decided to move on, despite having sunk much time and money in design and consultant fees.
We looked at Thermotech windows, which are made of pultruded fiberglass. This material is said to be as strong as but less costly than wood. It’s also stronger than vinylCommon term for polyvinyl chloride (PVC). In chemistry, vinyl refers to a carbon-and-hydrogen group (H2C=CH–) that attaches to another functional group, such as chlorine (vinyl chloride) or acetate (vinyl acetate)., but unlike vinyl, expands and contracts to temperature changes at the same rate as glass, thus ensuring a better long term seal between glass and sash. We heard mixed views from a few builders and homeowners we met with Thermotech windows. But after seeing the beauty of the Unilux wood core/aluminum clad windows, we knew we would not want to get a uPVC or fiberglass window.
We only looked at Passivhaus-certified wood-core, aluminum-clad windows. We narrowed our search to Intus  and Bieber  windows. (Intus also manufactures a Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. certified uPVC window at a much lower cost.)
Intus is manufactured in Lithuania, with a U.S sales office located in Washington D.C. Intus is a visible presence at many Passivhaus events. Maine Green Building Supply , located in nearby Portland, Maine, recently became an Intus retailer. How convenient!
Bieber is manufactured in the Alsace region of France, and has U.S. sales offices in Newport Beach CA and New York City.
Both Intus and Bieber are European-style tilt/turn windows. Both use high quality hardware with multiple locking points between the sash and frame and several gaskets around the perimeter to securely close the window. Both have thermal breaks in the window frame and sash: Intus uses foam between the aluminum claddingMaterials used on the roof and walls to enclose a house, providing protection against weather. and the wooden frame; Bieber uses an inert material routed into the core.
I traveled to the Intus sales office in Washington DC, and then the Bieber sales offices in Manhattan New York in early December. What a refreshing change: the sales staff were thoroughly knowledgeable about the technical details of their windows, AND were conversant with the Passivhaus standard.
I looked at window samples and asked dozens of questions: How is the frame assembled? Can the glazing be replaced without replacing the sash? Can gaskets be replaced? How is the cladding applied to the wood core? How do you adjust the hinges so the sash aligns perfectly within the frame? What glazing options are available? Can the windows be factory stained? What is the shipping, customs, and delivery process? Will a factory rep be present for unloading and offer technical assistance to install the first few windows? How are the windows installed? What is the warranty? How are warranty and replacement issues handled?
I liked what I heard and saw about both the Intus and Bieber windows. My overall impression was that these windows were exceptionally beefy, well engineered, meticulously assembled, and very attractive European-style windows. Since both windows were Passivhaus-certified (Unilux was not), both had reasonably similar performance in terms of frame widths, frame and sash U-factors, glazing U-factors, SHGC, and VT factors for PHPP input.
That’s not to say there are not differences between the two. The Intus windows can be factory stained (you choose from among a handful of stain options) at no additional cost, and overall the Intus windows were less costly than those from Bieber.
Bieber offers a very attractive concealed hinge for venting units at no additional cost, but there is an an additional charge for factory staining. Bieber also offers slightly better glazing (0.63 vs. 0.62 SHGC). Spread across an expansive south-facing glass, that 0.01 improved SHGC makes a noticeable difference in a cold climate when trying to attain the very low Passivhaus heating goal of 4.75 KBTU1,000 Btus.
Bieber offers other customization options, such as milling an angled slot to receive the side jambs when the window is installed in the rough opening. The window also features a very narrow exterior cladding profile; it’s designed to be “packed” with exterior styrofoam insulation during installation. This improves the frame U-factor, eliminating a thermal bridge within the window frame.
They are both very nice windows that would offer performance, comfort and elegance if installed in Edgewaterhaus. So how did we decide?
Screens! Screens were the primary tipping point in favor of Bieber. Screens are an absolute necessity here in Maine from late spring to the first frost. Mosquitos, gnats, horse flies, deer flies, and black flies abound, feasting on warm blooded skin. These tiny to large size buggers leave a bite trail of rose colored pinpricks to large welts on your exposed skin.
If you don’t have window screens in Maine, you might as well get non-venting windows. Edgewaterhaus is perched on a bend along the intertidal area of the Saco River, and the large marshy area by the river bank provides a prolific breeding ground for ‘squitos. So having screens on all venting windows was de rigueur.
As well made as the Intus windows appear, the fixed screens seem to be an engineering afterthought. (In our travels to Europe, we have noted few buildings had window screens.) The Intus fixed screens attach to the frame with a series of brackets that overlap and compress the outermost gasket on the window. At best, they look clunky when the window is open, and I wondered if the compressed gasket affects performance. Intus offers an exterior mount pull-down screen, but Edgewaterhaus has many windows units with a mix of fixed and venting window panes. We did not like the aesthetics of an exterior screen mounted over just the venting pane. The Intus sales rep said the factory is working on an improved fixed screen design.
In contrast, the Bieber screen mounts from the inside with a clasp that fits into a slot in the frame. We also liked the concealed hinge option for the sash. With this no cost option, all you see from inside is the wood sash and frame with no visible “door style” hinges typical of European style tilt-turn windows. Very nice!
So we decided to go with Bieber windows. The photo at the top of the page shows the Bieber Passivhaus window that we have selected for Edgewaterhaus: Bieber Optiwin window Wood/Aluminum series.
Our architect, Chris Briley, started to replace the Unilux windows in the CAD drawings with Bieber windows. The Bieber window has a much narrower exterior aluminum clad profile than the Unilux, as it is designed to be “packed” with exterior insulation. Chris said packing the frames would slightly reduce the thermal bridge in the wood frame, but would also move the window frame further into the wall, complicating exterior weatherproofing around the window frame. Bad tradeoff. So, no “packing” for us.
But the Bieber design also lent itself to be installed higher in the window rough opening, effectively adding several inches in height of higher performing glass within the same rough opening dimension. Now several inches of additional glass doesn’t seem like much, but spread it across the entire south facade, and now we’re talking something more substantial. The redesign of the west wing of the house, described in my previous blog, “cost” us 25 square feet of glass. Moving from Unilux to Bieber recaptured nearly all of this glass, which will surely help in the Passivhaus certification analysis.
Equally important, Chris has designed a recessed cavity to conceal shades above each window (at the interior side of the header). The detail still leaves some 6 inches of wall showing above the window. A very nice touch. The detail drawing (below) shows the recessed cavity.