Thermal Continuity in Window Design

08:52:00 AM on 07/07/2009

I’ve always hated drinking coffee through a lid.  It’s too much like a “sippy cup”.  But as I burned the skin off my upper lip this morning, I realized just how important thermal continuity is to the  entire coffee mug system.  Thermal continuity is important to a lot of things,  just as it is with Kawneer’s new single- and double-hung window, the AA®3350 ISOPORT® Window.

You can position the thermal break in many products almost anywhere you want and get decent results.  With Casement Windows for example, the ones that open and close like a door, the operable sash is nested in its frame, making it quite easy to align the thermal breaks and get good performance.  Single and double hung windows, where the top sash is in a different plane than the bottom, is an entirely different story. There’s two questions here, “How do you maintain a consistent  thermal break from the top to the bottom?”, and  “How do you keep the thermal break in the two sashes aligned with the thermal break in the frame? “  In fancier words - How do you maintain the thermal continuity?  It’s simple.  It’s all in the unique thermal break design of the AA®3350.

451PandD_White Thermally broken aluminum windows have been around for a long time.  Some use a method called “P&D” or “pour and de-bridge”.  With P&D,  a liquid resin is “poured” into an extruded channel, the resin quickly hardens and then the back of the channel is ripped out or “de-bridged”.  This splits the aluminum extrusion into two halves joined by the thermal break. (A typical pour and de-bridge extrusion assembly is shown at left - click image to enlarge.) Other thermal products, like the AA3350, are designed with stiff plastic strips or “dog bones” clamped between two individual aluminum extrusions.  This method allows much more design flexibility.


When you look at the outside frame of the AA3350, the first thing you notice is the large black plastic (actually polyamide) thermal break. (View of AA3350 polyamide thermal break used in frame jamb members shown at right - click image to enlarge.)  Because this type of thermal break is not nearly as limited as P&D, we can design it large enough to maintain alignment or continuity with the thermal break in the top and bottom sash.  A closer look at the unusual thermal break design  where the top at bottom sash meet in the middle shows how the thermal continuity is maintained from one plane to the other.  In the end, everything exposed to the weather on the outside is consistently separated from the inside.

  AA3350_Meeting_Rail Kawneer-234_webGr
Polyamide thermal breaks
used in frame members of
Kawneer's AA3350 ISOPORT Window.

Note how the thermal continuity is maintained between the frame and sash members .
(Click images to enlarge.)


So there… problem solved.  The next time you burn your upper lip on an aluminum window look for thermal continuity.  Now, I'd love to hear from you so, be sure to share your thoughts and comments.



Mr. Holcombe,

I am writing from the great area of Buffalo, New York. Notorious for having lots of snow and blizard conditions. If only our weather lived up to the reputation that has put us on the map, I would have a lot more fun with my passion of snowmobiling.

I am reaching out to you to know if you consider the 1600 wall to have a thermal break. Can you comment?

Also, can you describe the difference between the 1600 wall systems that you have. I believe there are a total of 4.

Thank you for your assistance.

Kirk Fitscher
Vice President - Construction
Ellicott Development
Buffalo, New York
(716) 854-0060



Excellent question Kirk. As far as the thermal breaks go, it depends on which 1600 Wall System we’re talking about.

Technically speaking, 1600 Wall System1 is thermally “improved”. A true thermally broken framing system is one that fully separates exterior exposed surfaces from interior exposed surfaces. This particular version of the 1600 Wall family of products is exterior glazed, which means the glass is installed from outside the building with screw applied pressure plates. The pressure plate fasteners are typically located at 9” on center. Upon closer inspection you can see the fasteners penetrate the pressure plate, pass through a thermal separator, and thread directly into the interior mullion. The threads of the fasteners bite into the mullion on two sides. Even though this is only creating incidental contact and a bridge (or short circuit) between the exterior and interior metal surfaces, it’s the thermal separator that provides the true benefit.

And… You are correct; there are a number of different “Systems” within the 1600 Wall family of products. In a nut shell:

1600 Wall System2 is simply the two sided structurally silicone glazed (SSG) version of System1 which eliminates the exterior vertical metal and provides an uninterrupted glass surface.

1600 Wall System3 is another thermally improved curtain wall where the glass may be set from either the exterior or interior. This makes the system quite suitable for low- to high-rise applications.

1600 Wall System4, a true “thermally broken” product, is an inside glazed system that utilizes a different type of thermal separator. System4 also has a narrower 2-1/4" sightline rather than the typical 2-1/2" sightline of our other 1600 Wall Systems. Inside glazing eliminates the need to stage a building on the outside to set glass and less exposed exterior metal improves thermal performance.

And lastly, 1600 Wall System5 is another inside glazed system, with yet a different type of thermal separator and a 2-1/2" sightline. This system has options that allow it to be used as a full curtain wall and also for horizontal ribbon windows or “punched” openings - providing a “one system fits all” solution.

Regardless of the application, there should be a 1600 Wall System that fits your need. Thanks for asking and trade your snowmobile for a Sea-Doo and come south sometime.

Best regards,


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