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Community and Q&A

Rain screen

AHTTAR | Posted in General Questions on

Hey guys…I’ve got some cedar lap siding installed over 3/4″ rainscreen, gap at the top and bottom of the wall. This is all installed over 2 1/2″ of ISO, tyvek, sheathing in that order. Soffit overhangs are 3′.

We had our first mild freeze last night (30F and 70F during day). It has been raining for the last couple of days so there was a bit of moisture in the air but not a ton. This morning I noticed the furring strips behind the siding showing up because that area of the siding was dry. Where there is just air behind the siding there was some ice/moisture on the face of the siding which is really what made the furring obvious. Didn’t have a camera sorry. Also roof had about 1/8″ of frost.

Inside the house is about 72 which is mostly from thermal heat gain the last couple of days. Radiant floors are set to 65 right now so it wasn’t turning on.

I just installed the siding and actually dipped them completely in lifetime wood treatment so I have to imagine they still have some extra moisture, but not a ton. Its all KD clear cedar.

I can’t imagine this is thermal bridging, more likely the furring strips being a bit warmer and keeping the cold air from circulating behind the siding.

This is a new process to me so I’m just trying to gauge potential issues to stay on top of any that might occur in a not so average hosue.


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  1. GBA Editor
    Martin Holladay | | #1

    You observed either dew or frost, or a mixture of both. This is a normal phenomenon, which is why you also noticed it on your roofing (and perhaps on your lawn).

    Cold air moving through your rainscreen ventilation gaps can certainly lower the temperature of portions of your siding. The furring strips keep some of your siding a little warmer.

    The source of the dew is moisture in the outdoor air. It collects on cold surfaces.

  2. AHTTAR | | #2

    Thats what I figured but always nice to hear it from someone smarter than me. Thanks Marin. My guess is once it actually gets cold out, the furring strips wont be as warm and this won't occur.

  3. Expert Member

    I bet you are right. The shoulder seasons are when I see strange moisture patterns here too.

  4. AHTTAR | | #4

    People must think we're crazy looking at all these tiny little details!

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