Mansard-Style Vented Roof
We’re in the planning stages of a new build in Southern Ontario (climate zone 5? 6?) and are starting to translate the schematic design into construction details.
Roughly speaking, the house is an L-shaped house framing a courtyard in the back. There’s a long-skinny single-storey wing running North-South on one side of the house which holds the great room (family room + kitchen) and has a simple gable roof on it (will have high cathedral ceilings inside). Let’s call this the GABLE wing.
It’s connected to a rectangular 2-storey East-West running wing that holds the rest of the house (living/dining/garage/bedrooms). This East-West wing has a mansard style roof on it. It has a 16/12 slope on all sides, and rises up about 8′ and then is flat across. Let’s call this the MANSARD wing.
Met with the architect and builder recently and we talked about how to build the roof. They both seemed to think that a vented roof for both the gable portion and the mansard portion would make sense, and they’d build it with a service cavity on the underside to house ductwork, electrical, lighting, etc. within the conditioned space.
This generally makes sense to me for the gable wing. I can imagine how a sufficient flow of fresh air will make its way from the soffit to the ridge to ventilate that roof.
But what about the Mansard wing? How does the whole idea of venting a roof work if there’s no ridge? There will be a series of mushroom vents (or maybe a different shape…but same idea) spread over the flat part of the roof.
Is venting this Mansard roof a good idea? Or should I be pushing the architect and builder for an unvented roof?
One last point. I’m planning to install solar panels on the flat portion of the Mansard roof. So most of the roof will be in the shade — which I understand may further impact the drying potential inside the attic.
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