Dormer Vents
I’m in Southern California. I’m in the process of getting re-roofing estimates for a cool roof with 3″ polyiso and concrete roof tiles. I plan to install rockwool between the rafters in the attic. By default, all of the contractors have added attic dormer vents to their bids. However my understanding is that a cool roof is to create a conditioned space in the attic and to seal any vents. I am going with a cool roof because I have a LOT of air conditioning ducting in the attic.
Before I tell the contractors to delete the dormer vents from their bids, might there be a reason that I would still want attic vents near the ridge, below all of the insulation? Maybe the cool roof would still get hot enough that I would benefit from some air circulation? Or I should completely seal up the attic?
Just trying to think of the reason the contractors spec’d the vents when they know I’m doing a cool roof..
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Replies
Sounds like what you are building is a roof with exterior insulation plus fluffy in the rafters. This type of roof should not be vented, adding vent to this type of roof negates the benefits of the insulation. Since the attic is now part of your conditioned space, you might need to add a supply vent from your air handler. Sometimes with older sub standard duct install, the existing ducting might leak enough to condition the space.
The 3" of polyio above the roof deck is more than enough for condensation control in your climate, it is a very robust and energy efficient roof.
You do want to spend some time sealing up your attic, make sure the soffit vents, gable vents or ridge vents are closed and all gaps filled with canned foam. You don't want to see any daylight in your attic.
That makes sense, thanks Akos! Yes the old metal ducting may have some leaks here & there which may be enough to condition the attic without an extra supply. In that case I will have them delete the dormer vents from the bids and seal up the attic.
ddbear,
To make a sweeping generalization from local experience (and probably offend Martin at the same time) - all the roofers I know are extremely skilled at putting on roofs, and repairing the substrate they need to fasten them to. Beyond that, their interest in understanding the workings of the roof assembly underneath is usually pretty low.