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SHEATHING, FOIL FACED - VENTS
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STAIRS, RAILINGS, LANDINGS, RAMPS
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SURFACE GRADING, SITE DRAINAGE
THERMAL EXPANSION CRACKS in BRICK
TREES & SHRUBS, TRIM OFF BUILDING
TRIM, EXTERIOR CHOICES, INSTALLATION
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WATER BARRIERS, EXTERIOR BUILDING
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WINDOWS & DOORS
Window condensation problem troubleshooting & repair: this article discusses problems with excessive condensation on windows and skylights and reviews the causes and cures of window condensation, secondary effects (mold, rot, decay), and also the condensation resistance of window glazing materials.
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In this article series we discuss the selection and installation of windows and doors, following best construction and design practices for building lighting and ventilation, with attention to the impact on building heating and cooling costs, indoor air quality, and comfort of occupants.
We review the proper installation details for windows and doors, and we compare the durability of different window and door materials and types. This article includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons.
To rate a window’s resistance to condensation, NFRC recently developed a method that evaluates the window’s frame, glass, and glass edge at a standardized set of temperature and humidity conditions.
Based on the coldest part of the window assembly, it is assigned a rating from 1 to 100.
The higher the rating, the better the window is at resisting condensation, but the rating doesn’t predict condensation under specific conditions. The voluntary minimum for a “thermally improved window” under the AAMA/NWWDA standard is 35.
The best protection against condensation is low-E glass with gas fill, combined with warm-edge spacers and a nonmetallic window frame, such as wood, vinyl, fiberglass, or one of the newer composites. Table 3-6 (below) provides a general guide to when condensation is likely to form on different types of glazing. Without warm-edge spacers, condensation will occur at window edges first.
[Click to enlarge any image, photo, or table]
Because warm moist air is carried upward by convection currents, skylights are often one of the first places to develop condensation. This can lead to dripping and staining of the frame, well, or furnishings below.
The best defense against skylight condensation is to choose high R-value glazing with warm-edge spacers. Good insulation of the skylight well also helps by keeping the surrounding area warmer. Several manufacturers offer skylights with integral condensation gutters, a helpful feature in cold climates.
The NFRC (National Fenestration Council) in discussing solar heat gain at windows, describes the Condensation Resistance of Windows (CR) as follows:
American Architectural Manufacturers Association (AAMA) www.aamanet.org
Efficient Windows Collaborative www.efficientwindows.org
National Fenestration Rating Council (NFRC) www.nfrc.org Sustainable by Design www.susdesign.com
Shareware calculators for sun angles, solar heat gain, and shading
Window and Door Manufacturers Association (WDMA) www.wdma.com
-- Adapted and paraphrased, edited, and supplemented, with permission from Best Practices Guide to Residential Construction.
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