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VENTILATION in BUILDINGS
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Window or skylight flashing & sealant application: here we provide best-practice details about flashing and sealing around windows to avoid air and water leaks. 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.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
See WINDOWS & DOORS our home page for window and door information, and also see WINDOW TYPES - Photo Guide for a photographic guide to window and door types and architectural styles. Ourlinks listed at Related Topics provide in-depth articles on window and door selection, inspection, installation, problem diagnosis, and repair.ction Chapter 3, BEST PRACTICES GUIDE: WINDOWS & DOORS:
While modern flange-type window frames appear to simplify window installation, how best to integrate the nailing flanges with the sheathing wrap and siding has been a subject of debate, and recommendations vary among different window manufacturers, sheathing wrap manufacturers, and contractors. The approaches shown below represent a broad consensus of leading manufacturers and experienced contractors, but other approaches that follow the same basic principles can also work. These are:
All clad and solid-vinyl windows come with an integral nailing flange or one that is friction-fit into a slot in the frame. In addition to simplifying the nailing, the flange helps to create a weather-tight seal at the head and sides of the window.
The most critical details are the head flashing, which should seal to the sheathing to pick up any dripping water from above, and the sill or pan flashing, which should freely drain to the exterior. The following approaches take advantage of the newer peel-and-stick flashing tapes, which have simplified the flashing of flange type windows.
Watch out: as our window photos above demonstrate, installing any window without proper flashing and sealing is likely to result in leaks into the building interior. The owner of this new home was very unhappy that each time it rained water ran down the inside of her walls at this window.
Figure 3-13 above shows how to flash a window installed after the plastic housewrap is in place. After cutting a modified “I” in the plastic housewrap, fold in the flaps, staple every 6 inches, and trim the excess.
When windows are installed before the building is wrapped, the key is to detail the pan flashing so it can properly lap over the housewrap. One approach is to leave the paper facing on the outer flap of the pan flashing so it can layer over the housewrap when installed.
Another approach, shown in Figure 3-15 below, is to seal the pan flashing to a flap of sheathing wrap that will be layered over the housewrap when installed.
Whether to seal the side window flanges directly to the sheathing or the housewrap is a matter of personal preference. Since few leaks originate at the sides of windows, either detail can work well as the flashings are detailed so each sheds water to the layer below.
When using felt paper, paper up to the bottom of the window. Then install the pan flashing, window, and side and head flashings as shown in Figure 3-15 just above.
To create a head flashing on round-top windows, one approach is to patch together several short pieces of flashing tape, making sure to start at the bottom and lap each upper piece over the preceding lower piece. Another option is to use a flexible membrane such as DuPont’s Flexwrap® tape, which can be bent to conform to the curve without cutting.
Where multiple windows are mulled together in the field, treat the space between the windows like a small section of sidewall. Make sure horizontal mullions are lapped properly so the sill flashing above laps over the cap flashing below. Use peel-and-stick flashing tape on vertical mullions, overlapping the vertical tape onto any horizontal mullions that intersect.
As an extra precaution against wind-blown rain entering behind the side casings, you can fold back the inside edge of the spline to form a one-inch hem, a detail developed by Pennsylvania contractor Carl Hagstrom.
At the head casing, a metal drip cap is required to protect the brickmold and provide a watertight seal. Slip the metal drip cap under the sheathing wrap and seal it to the sheathing with flashing tape.
-- Adapted and paraphrased, edited, and supplemented, with permission from Best Practices Guide to Residential Construction.
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