HardiPlank Lap Siding Butt Joint Flashing

By Todd Fratzel on Siding & Trim

HardiPlank Lap Siding Field Butt Joint Treatment

HardiPlank Lap Siding is a fantastic siding material that we’ve been using for years on both residential and light commercial building projects. HardiPlank Lap Siding is a fiber cement siding product that looks like wood clapboards but outperforms it when it comes to weather resistance and finish performance.

In order to benefit from this products excellent weather resistant properties it must be installed according to the manufacturers recommendations. One of those recommendations deals with properly flashing behind field butt joints. As you can see in the photo above we’ve installed a piece of flashing behind each field butt joint in order to keep water and moisture from getting behind the siding.

There are several products that can be used in this type of application. Some carpenters may choose to use heavy felt paper flashing while others may use metal step flashing as we’ve done in this example. What’s most important is installing the flashing correctly so that any water that enters the joint will be deflected down and out of the siding instead of behind it where it might damage the wall sheathing. If you look closely at the photo the flashing is just long enough to cover the top edge of the lower clap board but not long enough to be seen below.

Taking the time to install this simple flashing detail will ensure your next HardiPlank siding job lasts a very long time. Don’t rush and skip these little details as they will surely come back to haunt you!

About the author

Todd Fratzel

I'm full time builder for a large construction company in New Hampshire. I run their design-build division that specializes in custom homes, commercial design-build projects and sub-divisions. I'm also a licensed civil and structural engineer with extensive experience in civil and structural design and home construction. My hope is that I can share my experience in the home construction, home improvement and home renovation profession with other builders and home owners. I'm also the Editor-in-Chief and Founder of Tool Box Buzz. Please feel free to contact me if you have any questions, suggestions or you'd like to inquire about advertising on this site.

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  1. Bryan says:


    I came across this product for but joints thought it was a great idea

  2. Shawn says:

    How do you use flashing on Board and Baton siding?

    • Todd Fratzel says:

      Not sure I understand the question. Typically board and batten runs full length up and down, so there are no butt joints to deal with.

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