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Community and Q&A

how to ventilate old clapboard siding

bob_swinburne | Posted in Energy Efficiency and Durability on

I am (an architect) being asked a question about an old house 1904 – Zone 5 upstate NY – 2×4 walls, interior drywall, board sheathing, craft paper under clapboards.
The person is inquiring about adding insulation.  Perhaps pulling the drywall off and thickening the wall to 5 1/2″ then filling with a high density mineral wool batt or wood fiber batt. The concern is then that the old clapboards with a few layers of lead paint might be an effective vapor barrier and act as a condensing surface.  Not so good.
I seem to remember reading about adding a 1/2″ vent space in each stud bay at the back side of the sheathing prior to insulation.  I am wondering if anyone could point me to that article or if anyone has any input.
TIA – Bob


  1. Expert Member
    1. bob_swinburne | | #2

      Bingo! Thanks Malcolm!

  2. Expert Member



  3. conwaynh85 | | #4

    I agree that this approach would reduce the amount of interior moisture from reaching the siding and condensing. But it would also reduce the amount of heat moving through the wall and drying the existing siding. This approach also does not appear to have any air inflow or outflow in the "rain screen" and therefor cannot carry any moisture away if it gets in from the outside, which is likely. I think this is one of those situations were you let the existing heat flow dry the siding or create a proper rain screen with new siding. I very well could be missing something though...

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