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Does a parapet above a SIP really need to be vented?

DylanHenry | Posted in Building Code Questions on

We have a project with SIP roofs, and a super-insulated cavity wall system. It will be built in Ontario. The insulation will be spray foam, which seals the wall to the underside of the SIP.
On top of the SIP will be several wood parapets of varying heights, approx. 12″ max height. My questions is whether this parapet would need to be vented. I have based my detail on this page from Hammer and Hand,
which shows a very similar design to my project. Does the venting of this parapet actually serve any purpose? Could the parapet be completely sealed?

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  1. Expert Member


    Your parapets are right at the height H&H recommends starting to ventilate. I think even they would say you are safe.

    They identify the chief source of moisture as coming from the walls or roof below. As you are using SIPs, that significantly mitigates that as a problem.

    Even with higher parapets, I'm not sure cutting holes helps any more than it would in exterior wall sheathing. Something I did in the 90's that Martin cured me of.

    1. DylanHenry | | #2

      In general, is it correct to assume that a perfectly built parapet would only need to be vented because of the heat that would build up inside it? My parapets will be completely outside of, and isolated from, the heated interior of the building.

      1. Expert Member
        MALCOLM TAYLOR | | #3


        I can't see how any more heat would build up in a parapet than, say, an outdoor wall clad on both sides, or an attic. I've never heard of excessive heat damaging parapets.

        The problems I've seen with parapets have all been due to poor cap-flashing details, or integrating the roof membrane with the flashing.

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