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Looking Through Windows — Part 2

The next window manufacturers we investigated were Thermotech Fiberglass and Unilux

Image 1 of 2
Triple-glazed Unilux UltraTherm windows at the Coastal Maine Botanical Gardens. Unilux windows are manufactured in Germany.
Image Credit: Roger Normand
Triple-glazed Unilux UltraTherm windows at the Coastal Maine Botanical Gardens. Unilux windows are manufactured in Germany.
Image Credit: Roger Normand
Side view of a Unilux Ultratherm triple-glazed tilt-turn window. Traditional casement windows have a crank mechanism to open and close the window; the crank also serves to restrict any further movement of the window. There is no similar restrictive mechanism with European tilt-turn window like this window from Unilux.
Image Credit: Roger Normand

[Editor’s note: Roger and Lynn Normand are building a [no-glossary]Passivhaus[/no-glossary] in Maine. This is the sixth article in a series that will follow their project from planning through construction.]

In my last blog, I explained why we decided against using Schüco windows (quality and reliability concerns) or Pella windows (great windows, but with inadequate performance specifications for our needs). We reviewed the other 13 candidates under consideration, and opted to pursue two other high-performance, triple-pane window manufacturers: Thermotech and Unilux AG. (Note: unless you are proficient in German, consider clicking the British flag in the upper right corner of the Unilux homepage to translate most web pages into English.)

I had read about Thermotech windows in several articles on top energy performance homes published in the Journal of Light Construction and Fine Homebuilding, two highly regarded residential construction and remodeling monthly magazines that I read regularly. Thermotech is a North American window manufacturer with traditional crank casement windows that open outwards. Their frames are made of pultruded fiberglass, which my readings suggest is superior to wood, wood-clad, fiberglass, and PVC windows in terms of strength, and resistance to heat transfer. Pultruded fiberglass boasts similar expansion/contraction rates with glass.

Thermotech Fiberglass is slow to respond

Thermotech’s window performance specs were a bit better than Pella’s, but still not in the league of the European window manufacturers. Although a local distributor had dropped Thermotech because of alleged poor responsiveness from the manufacturer, we decided to go directly to corporate headquarters in Ontario, Canada.

Our architect, Chris Briley, has batted e-mails back and forth and played phone-tag with the corporate rep, but with little traction so far. We have insisted on being able to see and operate installed windows, and the corporate rep has promised, but not yet delivered, on opportunities to see homes with Thermotech windows.

Unilux windows from Germany

We will also pursue German-manufactured Unilux windows. Fortunately, Hancock Lumber, a major regional building material supplier with nine locations, is a Unilux distributor. We have been to Hancock’s Home Again retail location in Portland to view window samples of the Unilux Isostar PVC and Unilux UltraTherm wood-core aluminum-clad windows. We were quite impressed with the rugged construction of the samples. Even the tilt-turn feature of European windows is growing on us. The Hancock sales rep has given us two locations to go look at these windows installed in nearby buildings; one was the Coastal Maine Botanical Gardens in Boothbay Harbor.

So we set off to visit the Botanical Gardens. The Unilux rep had told me that I could see the Unilux UltraTherm wood-core triple-pane aluminum-clad window at the newly dedicated Bosage Family Education Center. This 8,000-square-foot two-level structure earned LEED Platinum status, features larges curtain-walls of windows, and numerous energy and environmental design elements like nano-gel filled energy-efficient skylights for daylighting.

There’s also a very unobtrusively designed rainwater collection system that feeds several underground cisterns for irrigation as well as flushing toilets. The 45-kW solar array is designed to meet the full electricity demand for the building, making it the first public building in the Maine to attain net-zero energy use.

Impressive! There’s even an interactive monitor that compares the features of the building to plant functions. Neat!

The heft of the Unilux windows is substantial and satisfying

We saw lots of Unilux UltraTherm windows. There were French doors, hopper windows, fixed windows, and tilt-turn windows. There were individual window units and several large curtain-walls – individual window units mulled together to form a massive wall of windows. The screens were nicely integrated into the outside of the venting windows.

I spoke briefly to the executive director, and several of the administrative staff, who all independently praised the quality of the the windows. Indeed, you can readily feel the very satisfying, substantial heft in opening or closing the heavy triple-pane windows. Yet despite their considerable weight they move easily and smoothly in “turn” mode on well-machined door hinges.

I was very impressed.

The windows need wedges to hold them open

One quibble: Traditional casement windows have a crank mechanism to open and close the window. The crank also serves to restrict any further movement of the window. There is no similar restrictive mechanism with European tilt-turn windows. Think of the wind swinging a door open and closed, unless you place a door stop under the door. I saw several wedge-shaped wood blocks used to pin the window in a fixed open position. The bottom gasket had detached from the slot in the sash in a few of these windows from the friction of the wedge.

The Europeans would likely say use the “tilt” function if you just want ventilation. Sure, but that only provides a small fraction of the ventilation area compared to the window “turned” fully to the open position.

A few days later, I went to Portsmouth, N.H., to view Hancock-supplied double-pane Unilux wood-core aluminum-clad windows being installed in a penthouse condo. I spoke to the crew installing the windows, who said they easily installed the units using a gasket around the outer perimeter of the window and were going to foam the gap between the window and the rough opening.

I am very impressed with the Unilux wood core windows! And will certainly return to Coastal Maine Botanical Gardens.

The first article in this series was Kicking the Tires on a Passivhaus Project. Roger Normand’s construction blog is called EdgewaterHaus.


  1. user-626934 | | #1

    Tilt/turn details

    It's my understanding that most of the tilt/turn window manufacturers can offer (as an upgrade) a locking mechanism for the "turn" feature, so the window can be turned open and secured in place at any point in its operating range.

  2. user-1024963 | | #2

    locking a tilt-turn in place
    Yes, a tilt-turn can have what we call a "lever operated brake" which allows you to lock the sash in any open position by turning the lever back to the locked position when the sash is open. We now offer this as a standard option. Another option is a "90 degree friction brake". It has a friction setting to allow the sash to open/close less freely, and also stops the sash from opening more than 90 degrees...helpful in most PH/NZ projects where windows are installed in the center of the wall.

  3. user-2069108 | | #3

    Appreciate the information
    Although this blog isn't generating a lot of discussion, I am sure that many people find what you are writing of great interest.
    Having looked into PH windows, I can understand your frustration. I contacted about 4 Canadian manufacturers via their internet "contact us" pages, and only Thermoltech got back to me. I wasn't asking for much other than to see their products when I take a trip to Canada (NS) later in the year.

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