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Expansion gaps & HardiePlank lap siding

JDLee | Posted in Construction Techniques on November 17, 2007 04:33am

For the past few days I’ve been helping a contractor I hired install HardiePlank lap siding on part of my home in San Diego. The siding is all mounted between 2×6 rough-sawn douglas fir trim pieces (which are on the corners and around the windows.

I noticed early on that he was fitting the lap siding pieces pretty tightly between the trim pieces.  I asked him if expansion was a concern, but he said it wasn’t with the cement product (of course, there are also the wood trim pieces, but I don’t recall what he said about those).

But I just read an FHB article (“Working with Fiber-Cement Siding”) from June/July 2001 that states that on walls 12′ or longer, Hardie recommends you leave 1/8″ gaps between the lap pieces and the trim, and between the butt ends of adjoining lap pieces, to allow for expansion.  It recommends filling the gaps with caulk.

This wasn’t done with my siding, and my walls are 18′ long. 

Can anyone tell me from experience if this is likely to cause a problem? 

There’s not much I can do about it now, but I guess I could try to pull off some of the trim pieces and rip or route them down.  I really need the voice(s) of experience on this.  Thanks.

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Replies

  1. RobWes | Nov 17, 2007 05:36am | #1

    I have runs on my home that are near 40' with zero room for expansion or contraction. The entire job (siding) was cut on a saw and all joints are tight. To date I would not have it any other way.

    As for the movement of the AZAK.... That's a whole different story. Not very pleased is a good start for that conversation.

    1. JDLee | Nov 17, 2007 06:00am | #2

      Wow, it's great to hear that. 

      And I'd appreciate input from anyone else with experience, too.

      What is AZAK?

      1. runnerguy | Nov 17, 2007 02:55pm | #7

        Azek is a plastic trim.

        http://www.azek.com/

        Doesn't rot or absorb water but it does expand and contract with heat.

        Runnerguy

  2. splintergroupie | Nov 17, 2007 06:17am | #3

    I had a friend whose Hardie was left outdoors and got wet before installation. They butted the seams, but ended up with gaps of about 1/4', he told me, when it dried out.

    Mine was stored dry, and i butted the seams fairly close. My longest uninterrupted course is 42' feet, so you've got nothing to worry about. Moral: make sure it's not wet when you hang it.

    BTW, i spritzed caulk in the joints, let it dry, then caulked a second time. The joints are all but invisible now rather than sunken like some i've seen.

    1. JDLee | Nov 17, 2007 06:24am | #4

      Well, it's been really hot and dry here in San Diego, and my HardiePlank certainly hasn't gotten wet.  And my 2x6 trim was fairly wet, so, if anything, I guess I'll end up with too much of a gap (which is much better than expansion with nowhere to go).

  3. Scott | Nov 17, 2007 08:40am | #5

    2X6 rough sawn DF trim? Got pics? I'd really like to see how that looks. We're going with 2x4 RS cedar.

    Scott.

    Always remember those first immortal words that Adam said to Eve, “You’d better stand back, I don’t know how big this thing’s going to get.”

    1. JDLee | Nov 17, 2007 09:33am | #6

      I'm not quite at the photo-taking stage yet, but I will try to remember to post some when I am.

      I'm going with the 2x6s because it roughly approximates the siding style on the front of my house (the sides are stucco, and you can't see both areas at once, so it doesn't need to match too closely).

      So it's not really a style that I've chosen.  But I have to say that I couldn't see using 2x4s.  They would be way too narrow in comparison to the siding (at least the siding I'm using, which is about 8"-9" wide).  Of course, it depends on the style of your house, but if you're getting rough-sawn, I'm guessing it is somewhat like mine.

  4. User avater
    DDay | Nov 17, 2007 03:08pm | #8

    Hardie used to say in their install instructions to leave a gap, at the time of the article, that is what they were saying. Now they say "moderate contact". In an environment so dry like san diego, you should be fine.

    Azek is a pvc trim product that most feel is a great product, you just need to deal with the expansion. There are some negative with Azek and other pvc trim like Kleer, Koma, etc. They cost about $1 per ft more than primed pine trim and when you cut it the dust is like sugar and has a static charge so it sticks to you and all the tools. Azek site is http://www.azek.com

  5. Jim_Allen | Nov 17, 2007 04:53pm | #9

    I wouldn't worry about it. You live in a climate that is very stable.

    In MI, we often install materials in very cold weather. Gapping it then (slightly) makes sense because when it heats up in the summer, it will grow slightly. In summer, I always installed it touching but I also always left the ends gapped against window trim. I also tucked most of the siding under corner boards so almost every piece had a place to go if it decided to grow.

    FKA Blue (eyeddevil)

    1. newbuilder | Nov 21, 2007 10:12am | #10

      I notice in that FH article that they do NOT lay down furring strips to create a gap for air-circulation behind the installed hardiplank.  But I've heard that this is "proper installation procedure".  I'm putting up some of this over the next few days.  Does anyone know if it's 'OK' NOT to use the under-furring?  I'd rather NOT!!!

      Thanks -

      1. MikeHennessy | Nov 21, 2007 04:43pm | #11

        James Hardie thinks it's OK.

        http://www.jameshardie.com/pdf/install/install_plank_west.pdf

        Mike HennessyPittsburgh, PA

        Edited 11/21/2007 8:44 am ET by MikeHennessy

        1. newbuilder | Nov 21, 2007 10:11pm | #13

          thanks Mike!

  6. TJK | Nov 21, 2007 08:11pm | #12

    I caulk the butt joints as each piece goes up, leaving a 1/16"-1/8" gap. Two years later, -12F to 110F, they still look tight.

  7. KenVG | Aug 14, 2020 09:45pm | #14

    I see some of you guys have used caulk on the butt joints, and it seems successfully. from what I've read, they advise against using caulk on the butt joints, because the caulk will turn a different color over time, and you'll have a splotchy appearance. Have you found his to be true? Or, have you painted it after you caulked? I'm using the prepainted, so this may be why they say not to caulk.

  8. user-5885160 | Sep 03, 2020 04:47pm | #15

    I used the color matched caulk for all seams and the match is perfect. Now it has only been up for 2 years but I see no difference in caulk color vs. siding color. The caulking is also paintable so if you color match the siding with some good paint, you can always go back and do some touch up but I do not think it is needed.

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