Siding butt joint back-flashing from Tamlyn: Proline Plank Flash (C) InspectAPedia TamlynFiber Cement Siding Maintenance
How to protect fiber cement siding from water & weather damage

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Fiber cement siding maintenance recommendations from Certainteed™, James HardiePlank™ & other sources.

This article describes steps to protect building siding from water damage, plant damage, weather damage in general, giving clearances as well as sealing & caulking advice. We include sources for back flashing and H flashing that can be retrofitted to leaky or loose building siding to improve its weather resistance. Page top photo: Tamlyn's back flashing product recommended when lap siding was installed.

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Manufacturer's Advice for Maintaining & Protecting Fiber Cement Siding [CertainTeed & JamesHardie]

Fiber cement siding (C) Carson Dunlop Associates

Adapted & excerpted from CertainTeed Corporation's "CertainTeed WeatherBoards™ Fiber Cement Siding Installation Manual" [5a] and from "Fiber Cement Siding Best Practices for Effective Job Site Management"[5b] and from JamesHardie Corporation installation instructions and bulletins for JamesHardie HardiePlank lap siding. [12][12b]

Moisture Management and Gutters & Fiber Cement Siding Avoids Water Damage

Water management is key to protecting every part of your home, including your siding. Each area of the country is affected by moisture, whether it’s an occasional thunderstorm, high levels of rainfall or heavy snow accumulations.

The resulting moisture has potential to cause damage if not managed effectively. We recommend protecting your home from rainfall with gutters and downspouts. Divert or remove heavy snow accumulations that may stand against the siding for extended periods of time. And you should always be sure that your drainage system is free of debris and working properly.

Details: See

Shrubbery & Fiber Cement Siding, Recommended Distances

Proper moisture management also involves managing your landscape. Plants hold moisture, so any trees or shrubs that are close to your home should be trimmed periodically. Plants should not come into contact with your siding. Also, sprinkler systems should be adjusted to not saturate areas near your home.

Clearances for Fiber Cement Siding to Ground, Walks, Patios, Shrubs

Maintain required clearances and drainage slopes to ensure that moisture is diverted away from your siding at roof lines and ground level. Proper clearances include 1 inch from concrete, roof lines, patios, etc., and 6 inches from the finished grade. Landscaping should not reach the siding.

This refers to clearances from siding lower edge to ground, horizontal clearances to shrubs, &c. For details about siding gaps and clearances to other building components see Certainteed WeatherBoard fiber cement siding gap & caulking specifications

Re caulking Fiber Cement Siding - vs Installing H-Covers to Cover Siding Butt Joint Gaps

It is normal for building products located on the exterior of a home to expand and contract with temperature changes. To ensure a successful siding installation, you must allow for this movement during installation.

While CertainTeed WeatherBoards Fiber Cement siding does not experience the same rate of expansion and contraction as many other building products (such as wood), over time you may notice movement of the siding, specifically at the butt end/joints. This issue is mainly an aesthetic issue and should not create a condition that would cause long-term product failure. If you are dissatisfied with the appearance of the butt end/joint locations and wish to address them, CertainTeed recommends that you apply H-covers at the joint locations.

You will see vertical lines where each H-cover is installed, but then in our OPINION there were vertical lines already visible at the butt joint. And we agree with CertainTeed that this approach is likely to be more attractive than blobbing or smearing caulk into butt joint openings - a procedure that changes the texture of the siding and its coating performance or re-painting performance and appearance in a way that can be far more ugly, leaving roundish smears at every butt joint so treated.

Watch out: even the H-cover solution to siding board butt joint gaps is not without possible trouble. What are the chances that the plastic or aluminum of the H-cover will weather and change color at the same rate and in the same hue as the paint or coating on the siding boards? I'll bet zero. So over time these covers may become more noticeable.

Details about cures for the cosmetic problem of gaps at lap siding butt joints as well as for wall leaks at these locations are found at SIDING, FIBER CEMENT GAP CURES.

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