Best Practices Guide to Wall Siding, Trim, & Finishes on Building Exteriors InspectAPedia® -
Building wall siding flashing details & materials
Water leakage through building exteriors, cause, cure, prevention
Rain screen principle
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This article discusses best construction details for flashing building exterior siding to prevent leaks and water damage. This article series discusses best practices construction details for building exteriors, including water and air barriers, building flashing products & installation, wood siding material choices & installation, vinyl siding, stucco exteriors, building trim, exterior caulks and sealants, exterior building adhesives, and choices and application of exterior finishes on buildings: paints, stains. This article series includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons.
Proper detailing at joints, corners, and openings makes for
an attractive and durable job. Key details follow:
Lap Joints. The IRC requires that horizontal lap sidings
have a minimum one-inch lap joint, or 1/2 inch if the siding
is rabbeted.
Weather-proofing Butt Joints in Building Siding
In most climates, it is a good idea to slip a
small spline of asphalt-felt paper behind each butt joint in
horizontal sidings.
Layer the spline so it overlaps the piece
of siding below, directing any water out onto the siding
(see Figure 1-12 at left).
All end grain in the siding should be sealed after cutting
with a water-repellent preservative (WRP) or primer.
Building Siding Flashing & Finish Details for Building Corners
Use overlapping 1x4s or 1x6s at outside corners
or use 5/4 stock for a heavier look. Use a felt paper
spline, wrapped around the corner and extending 6 inches
beyond the corner board, to protect the joints where the
siding meets the corner boards (see Figure 1-5 at left).
Use a square length of 5/4 stock at inside corners with a
spline underneath. All end grain in the siding should
be sealed after cutting with a water-repellent preservative
(WRP) or primer.
With the spline, there is no need to
caulk the joint. With no caulk, the joint is free to dry out
when wet.
Flashing Details for Windows and Doors
If windows and doors are properly
protected with splines of felt or flashing tape, there is
no need to caulk the joints where siding meets the side casings.
At the top of a door or window, always direct the
sheathing wrap over the head flange or cap flashing. Never
caulk the joint between the siding and the head casing or
the sill, leaving these joints open to drain any trapped
water.
Siding Details At Roof-Wall Joint Step Flashings to Avoid Rot
Stop wood sidings at least 1 inch
short of the bottom leg at step flashings and other
roof flashings.
Otherwise water will wick up into the
flashing leading to paint failures and decay (see Figure 1-6 above left). Our wall siding photo (above right) shows the beginning of deteriorating wood clapboards that were installed touching the surface of an abutting lower asphalt shingle roof.
Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education.
Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com.
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John Rudy, Advantage Home Inspections, Flemington N.J. 08822 home inspector, 908-806- 6364, Home, Radon & Termite Inspections, Central & Parts of North New Jersey, email: jonadvantage1@yahoo.com
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