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Community and Q&A

Rainscreen over cedar

Gart103 | Posted in Green Building Techniques on

Currently have lap cedar on the condo over Tar Paper.
Wishing to put Hardi Plank siding over top.  Some contractors are saying there is no need to use the rainscreen system since cedar already breathes.  I have my doubts since we leave next to the ocean. I would like to use a house wrap then rainscreen and Hardi cement board siding on top.
What do you recommend?

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  1. Jon_R | | #1

    The cedar breathing has little to do with rainscreeen effectiveness. Are you comfortable that some air can flow behind the Hardi without adding a gap?

  2. Expert Member


    There are a couple of variables at play when deciding whether a rain-screen is necessary, or just good practice. One is the climate you live in. The other is how the existing wall is designed to dry.

    In marine climates and exposed sites rain-screens can be seen as a necessity. In most others, barring those with wildfire risks, they are good idea.

    If you have an interior vap0ur-barrier, and the wall relies on drying moisture to the outside, rain-screens help allow this - especially with a cement-based siding which can also draw moisture through it on sunny days.

    A couple of other points which may or may not be relevant:

    - Lap siding is not flat enough to apply another cladding on top. if that's what's there now, you have no choice but to strap before re-siding.

    - Whether you strap under the new siding or not, your window and door trim may need to be extended to cover the butt ends.

    - Check with your condo board and get their approval before agreeing on any changes to the exterior.

  3. insaneirish | | #3

    > Currently have lap cedar on the condo over Tar Paper. Wishing to put Hardi Plank siding over top.

    Why do you want to cover cedar with fiber cement?

  4. Gart103 | | #4

    Our lap siding is flat and doesn't overlap. The window and door trim is a problem but since our windows are aluminum and do not have a brickmould we can manage to create a good trim look.
    I am mainly concerned with cement board causing condensation on the backside which will then soak into the cedar and cause rotting overtime. I also was planning on a housewrap under the strapping.
    Am I ou to lunch?

    1. Expert Member
      MALCOLM TAYLOR | | #7


      If you put house-wrap over the unlapped lapped cedar siding, it can be seen as another layer of sheathing, and you end up with much the same wall as 99% of the houses being built with cement-based siding today. Does a rain-screen improve it? Sure - but there isn't a lot of evidence that in most circumstances walls without one suffer premature deterioration.

  5. Gart103 | | #5

    Why cement board over cedar?
    Good question but all goes to bad paint. The siding is about 27 years old which for cedar is not old but someone in their wisdom painted the cedar using a paint that places a shark skin on top. This doesn't allow the paint to breathe. eventually some cracks occurred in the paint and moisture got in behind and soaked into the wood. Since the sharkskin would not allow the wood to breath the wood just kept soaking up the moisture. To repaint we would have to plane the entire exterior. No painter will do this anyway. cheaper to reside. We tried to scrape and grind the paint off but the wood would take months to dry to a point of allowing paint to penetrate. We tried it but it will not adhere good enough.

    That's the story. Conclusion never use paint on cedar stick to penetrating stains.

    1. Expert Member
      Dana Dorsett | | #6

      >"Conclusion never use paint on cedar stick to penetrating stains."

      Never say "never".

      Cedar that has been...

      ... painted with acrylic latex primer on all sides at the factory...

      ... primer painted on the ends at every cut...

      ...painted only with acrylic latex paint, and...

      ... has at least some amount of drainage/breathing space between the back side and the sheathing...

      ... has a very good record at keeping both the paint & siding in good condition for the long haul.

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