|
|
How to Install Window & Skylight Flashing & Sealants
|
InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
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.
Installation Guide to Window Flashing & Sealing
This article includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons.
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:
- Always lap higher flashings over lower to shed water.
- Do not rely on caulking as a waterproof barrier, as it is
likely to fail over time. (CAULKS & SEALANTS, EXTERIOR)
- With heavy exposure to wind-driven rain and snow,
use pan flashing to protect the sill and use flashing
tape to seal the head flashing to the sheathing.
- Leave horizontal joints unsealed at the top and bottom
of the window frame to allow trapped water to escape.
Window Installation, Flange-Type
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.
Installing Housewrap at Window Openings Before Installing the Windows
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.
- Pan flashing. The next step, the pan flashing, is often
omitted but is critical for leak-free performance in
harsh weather exposures. The pan flashing can either
be a custom metal pan, an adjustable plastic pan, or
one formed in place from flexible flashing tape, as
shown (Figure 3-14 below). If using flashing tape, first add a
piece of beveled wood siding to the rough sill, sloping
to the exterior. Remember to increase the rough opening
height by
1/2 inch. Add patches of flashing tape to
bridge the gap at the cut corners.
- Install window. Next install the window, slipping the
top flange under the housewrap. Most manufacturers
recommend bedding the side and top flanges in a bead
of high-quality sealant to create a backup seal, a good
idea in harsh weather exposures. Do not caulk the
bottom flange, however, which must be left unsealed
so any trapped water can freely drain. To facilitate
drainage at the sill, set the window on shims.
- Side and head splines. Side splines of peel-and-stick
flashing tape go on next, sealing from the window
flanges to the sheathing wrap, extending 6 inches
above the top of the window opening and lapping over
the pan flashing. Finally, the head spline is slipped
under the housewrap, sealing the window’s top flange
to the sheathing. Patches of tape seal the diagonal slits
in the housewrap.
- Drip cap. If the window is trimmed on the exterior
with wood casings, use a metal drip cap on top of the
head casing and seal the drip cap to the sheathing tape
with peel-and-stick flashing tape. When the siding is
installed, do not caulk the horizontal joints above or
below the window, which would create a water dam.
Leave all horizontal joints unsealed to drain away any
trapped water.
|
Figure 3-14: Formed-in-Place Pan Flashing for Windows or Doors.
As we note above, the pan flashing can either
be a custom metal pan, an adjustable plastic pan, or
one formed in place from flexible flashing tape, as
shown (Figure 3-14 below).
If using flashing tape, first add a
piece of beveled wood siding to the rough sill, sloping
to the exterior. Remember to increase the rough opening
height by
1/2 inch.
Add patches of flashing tape to
bridge the gap at the cut corners.
|
Installing Windows Before Housewrap
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.
Figure 3-15: Installing Flange Type Windows Before the Sheathing Wrap is Applied
|
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.
Felt Paper Flashing or as Housewrap Around Windows
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.
When
installing the building paper later, layer successive courses
over the side and head flanges, setting them into a bed of
sealant at the sides of the window (see Figure 3-16 at left).
Leave the building paper unsealed at the head flashing,
however, to allow any trapped water from above to escape.
|
Head Flashing Details for Round-Top Windows
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.
Sealing Details ford Mulled Windows
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.
Window Installation, w/ Integral Brickmold
As reported in Best Practices Guide to Residential Construction Chapter 3, BEST PRACTICES GUIDE: WINDOWS & DOORS:
If installing windows with integral brickmold, proceed the
same way as shown for flange-type windows above.
However,
since there are no side flanges on the window, the
brickmold goes over the side splines, which can be either
felt paper or flashing tape.
Flashing tape is of less value with
brickmold since the windows have no flange to seal to.
Apply a continuous bead of sealant on the backside of
the brickmold before installing the window (Figure 3-17 at left)..
|
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.
Frequently Asked Questions (FAQs)
...
Ask a Question or Search InspectApedia
Questions & answers or comments about installing window or door flashing or sealant or caulk.
Ask a Question or Enter Search Terms in the InspectApedia search box just below.
Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- Basic Housing Inspection, US DHEW, S 352.75 U48, p.144, out of print, but is available in most state libraries; New York State version, ca 1955, source of our window parts and window repair sketches.
- Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Amazon.com and also Wiley.com. See our book review of this publication.
 Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference Book, a reference & inspection report product for building owners & inspectors.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones.
Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
- The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
- The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
 The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.
|
- Decks and Porches, the JLC Guide to, Best Practices for Outdoor Spaces, Steve Bliss (Editor), The Journal of Light Construction, Williston VT, 2010 ISBN 10: 1-928580-42-4, ISBN 13: 978-1-928580-42-3, available from Amazon.com
- The Journal of Light Construction has generously given reprint permission to InspectAPedia.com for adaptations, quotations, or reproductions used at this website. All rights and contents of the JLC material are ©Journal of Light Construction and may not be reproduced in any form.
- ...
|
