Jamie asks:I'm trying to locate the data for thermally broken window walls. I've seen LEEDS (sic) literature showing numbers for the savings when using thermally broken aluminum systems. Can you direct me to any LEEDS (sic) items regarding thermal breaks?

Answer: Hi Jamie, obviously there are several advantages of thermally broken window systems (as well as thermal breaks in the building envelope) as far as energy management and control strategies are concerned. Unfortunately I’ll preface with saying that I’m not familiar with any specifically referenced material in regard to thermal breaks in any LEED reference guides that I’ve seen (beyond a proposed fenestration description under EAc1 in the BD+C reference guide.)

For those that are unaware, a thermal break is essentially a measure implemented in building envelope construction to inhibit the passage of heat (or thermal energy) in or out of a building or space. Thermal breaks include low-conductivity materials of various types. Examples of various thermal breaks include:

1.A continuous metal structure that extends from outside to the inside of a building.

2.A u-shaped EPDM weather seat at the bottom of an exterior door

3.Insulating material between aluminum frames in windows

Aluminum window frames are popular for a large variety of reasons. It’s relatively inexpensive, can be extruded into a variety of shapes, typically very durable with lower maintenance concerns, and is relatively easy to anodize. All that being said, aluminum is also a great conductor. This increased conductivity can dramatically affect a building’s overall heat gain or loss without inclusion of a thermal break.

For a residential home, installation of insulated glazing with thermally broken frames can result in total yearly energy savings up to 20%. Energy cost savings for windows with various properties can be calculated through construction of a building energy model (typically the route for commercial building design) or, alternatively quick comparison calculations can be performed through online tools such as The Efficient Windows Collaborative (http://www.efficientwindows.org/selection.cfm) or the National Fenestration Rating Council’s Certified Products Directory (http://cpd.nfrc.org/search/searchdefault.aspx).

While LEED does not certify or endorse specific building products, there are a number of programs out there that do. I do know that PPG, for one, has established that its entire line of high performance architectural glass product should be Cradle to Cradle Certified at the Silver level. Cradle to Cradle Certification “provides a company with a means to tangibly, credibly measure achievement in environmentally-intelligent design” more information at http://www.c2ccertified.com/

The bottom line on thermal breaks is to take them into consideration whenever you’re building a high performance building. It’s just one additional strategy that adds up to the end goal of energy savings.

Hope this helps,
Sarah Gudeman, LEED AP

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