Passive vent (A.K.A. vapor diffusion port) at peak of a single-slope shed roof to wall?
Hi GBA friends,
I have a dilemma. In the rush of construction I didn’t really think the roof ventilation out properly. So sadly this will be a retrofit to some extent.
I have attached bathroom (left) and kitchen (right) single slope shed roof in the same plane only in the top 8 inches.
The kitchen rafters have been stuffed with Rockwool Batt with no soffit ventilation. There are two surface mounted lights in the ceiling.
The bathroom drywall has been removed and there is a single soffit hole (3″) which was intended for a bathroom exhaust fan.
My plan is this and I would love comments as I am trying to achieve best practice within time and cost limits.
Install passive vents at the highest points in both kitchen and bathroom roof assemblies.
Close off 3 in soffit hole, install a wall vented bathroom exhaust fan, leave a one and a half inch gap above rockwool batt, and a 2″ inch layer of foam to the interior of the rafters, air seal, drywall.
Remove ceiling fixtures and replace with air sealed or wall mounted fixtures.
Best,
Bridgette
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Bridgette,
Your explanation is confusing. You wrote about a 3-inch "soffit hole," but the photo shows a round penetration for the bath fan that is in the wall, not the soffit.
You wrote about "passive vents" installed "the highest points in both kitchen and bathroom roof assemblies." What is a "passive vent"?
For information on safe ways to insulate this type of roof assembly, see this article: "How to Build an Insulated Cathedral Ceiling."
Hi Martin,
Sorry for the confusion. The vent on the wall is for a stove exhaust fan and the soffit vent is on the left.
I am interested in this profile vent: Duraflo 60PRO50BL Pro 50 Roof Vent, Black https://www.amazon.com/dp/B004Y74THA/ref=cm_sw_r_cp_apa_Mss7BbAM2RND4
Originally I was interested in these vapor diffusion ports from smartvent, metalera and coravent but was hoping due to the small roof size, I could use only a single vent and make it an easier fix.
Bridgette,
I think you are confusing vapor diffusion ports (which allow no air movement whatsoever) with conventional roof vents (which are designed to allow for air movement through the vents).
The type of vent you need is one of the three shown in your last comment (Comment #5). The reason is that you need ventilation in every single rafter bay. One vent in the middle of the roof won't work.
Your plan to have a vented roof assembly will only work if you have a continuous soffit vent at the soffit. The vent must provide a fresh air intake for every single rafter bay.
For more information on vapor diffusion vents -- an approach that is inappropriate for your dilemma -- see this article: "Vapor Diffusion Ports."
I do not have the appropriate pitch for a roof to wall vent that tranverses the length of the roof. But I do have a cavity beneath the bathroom window but above the original kitchen additon roof (see shingles in picture) so similar to an unconditioned attic. This would allow soffit vents in each bay and a single vent at the roof to wall.intersection.