ASHRAE Journal - June 2020 - 82

COLUMN BUILDING SCIENCES

risks if implemented incorrectly. One approach to controlling ductwork sweating and burying standard ductwork and boots (insulated to less than R-13 in IECC Climate
Zones 1A, 2A, 3A) is to seal (or not install) sofﬁt vents, and to
install a "vapor diffusion vent or vapor diffusion port" at the
upper part of attic spaces and sloping rafter roof assemblies
(Figure 2) and yes we were here before ("No Sweat," ASHRAE
Journal, April 2016). Doing this we get "unconditioned
unvented attics." Yup, add a new phrase to the vocabulary.

Danger! Danger!†
Because there is so much condensation occurring on
ductwork in vented attics in hot, humid climates folks
are retroﬁtting the attics to be unvented. When both
constructing conditioned unvented attics and unconditioned unvented attics and retroﬁtting attics to become
conditioned unvented attics and unconditioned unvented
attics, it is critical that only sealed combustion appliances

such as gas furnaces and gas water heaters are installed
in such unvented attics. Let me repeat this a little differently-if you are stupid you can die. Please don't be stupid.

Bibliography

Lstiburek, J.W. 2015. "Venting vapor." ASHRAE Journal (08).
Lstiburek, J.W. 2016. "No sweat." ASHRAE Journal (04).
Lstiburek, J.W. 2017. "Hybrid assemblies." ASHRAE Journal (10).
Ueno, K., J.W. Lstiburek. 2015. "Building America Report Field
testing of an unvented roof with ﬁbrous insulation, tiles, and vapor
diffusion venting." Building Science Corporation, https://tinyurl.
com/ya25tclh.
Ueno, K., J.W. Lstiburek. 2015. "Building America Report Field
testing of unvented roofs with asphalt shingles in cold and hothumid climates." Building Science Corporation. https://tinyurl.
com/y6vjm3b4.
Ueno, K., J.W. Lstiburek. 2016. "Monitoring
of two unvented roofs with air-permeable
insulation in Climate Zone 2A." Thermal
Performance of the Exterior Envelopes of Whole
Buildings XIII International Conference. https:// https://bit.ly/2YUre1l
Rate this Column
tinyurl.com/y7fhu9oq.

†Phrase

TIME IS OF THE ESSENCE

ArmaFlex Ultra
®

with FlameDefense™ technology - the first elastomeric
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emergency, it gives you time.
www.armacell.us

ASHRAE JOURNAL

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J U N E 2020

uttered by Robot B9 from the TV series "Lost in Space" when someone is about to do something stupid. Robot B9 is not to be
confused with Robby the Robot from the movie Forbidden Planet. Robby the Robot came to life in 1955-the same year I did. Robot B9
was on television in 1967, the last year the Toronto Maple Leafs won the Stanley Cup.

https://tinyurl.com/ya25tclh https://tinyurl.com/ya25tclh https://www.buildingscience.com/documents/building-america-reports/ba-1409-field-testing-unvented-roofs-asphalt-shingles-cold-and https://www.buildingscience.com/documents/building-america-reports/ba-1409-field-testing-unvented-roofs-asphalt-shingles-cold-and http://www.tinyurl.com/y7fhu9oq https://www.bit.ly/2YUre1l http://www.tinyurl.com/y7fhu9oq http://www.armacell.us https://www.ashrae.org/

ASHRAE Journal - June 2020

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