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Discussion Starter #1
About 6-8 feet. The way the upstairs bathroom shed dormer was built, there was just no other way to stop airflow. The plumbing supply and waste lines exit and enter the exterior wall right at the edge of the soffit, so we have always problems with frozen lines. I just stuffed the cavities completely full with batt insulation and cut and fit foam board along the soffit opening. There was NOTHING to stop the airflow from entering the soffit and going under the floor. Much better now. The floor is warm up there for once and there is no cold air blasting from under the sink. Whoever designed that needs kicked in the rear...
 

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retired framer
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About 6-8 feet. The way the upstairs bathroom shed dormer was built, there was just no other way to stop airflow. The plumbing supply and waste lines exit and enter the exterior wall right at the edge of the soffit, so we have always problems with frozen lines. I just stuffed the cavities completely full with batt insulation and cut and fit foam board along the soffit opening. There was NOTHING to stop the airflow from entering the soffit and going under the floor. Much better now. The floor is warm up there for once and there is no cold air blasting from under the sink. Whoever designed that needs kicked in the rear...
If this is soffet area under a floor that over hangs, that will be fine.
 

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Discussion Starter #3
If this is soffet area under a floor that over hangs, that will be fine.

It's weird. There is like 2 foot run of roof slope from the front wall of the dormer to the soffit. There was no airflow to the attic, just under the floor. It has been a nightmare in the wintertime.
 

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The floor joist cavities should be insulated at interior of the rim joist.
Blocking the soffit vents and filling the cavity with insulation is not the correct solution in any scenario.


Could be you have no rim joist, or perhaps blocking should be put in. Some pics would help. Pipes insulated?
 

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Think I understand now after your last comment. You essentially have rafter tails projecting out under a dormer addition. The rafter bays were never sealed off.


That would be my recommendation, block the cavities with lumber or plywood. And insulate from the inside.
 

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Discussion Starter #6
The floor joist cavities should be insulated at interior of the rim joist.
Blocking the soffit vents and filling the cavity with insulation is not the correct solution in any scenario.


Could be you have no rim joist, or perhaps blocking should be put in. Some pics would help. Pipes insulated?

There was no way to insulate from the inside. The only access was to remove the soffit, insulate the cavity and the seal it off with rigid foam. That or wake up to a busted line one cold morning. I chose to take my chances with blocking the soffit.
 

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retired framer
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It's weird. There is like 2 foot run of roof slope from the front wall of the dormer to the soffit. There was no airflow to the attic, just under the floor. It has been a nightmare in the wintertime.
So it looks like a skirt roof on the side of the house but just part of the roof that left in place when they added the dormer. That section does not need venting. :wink2:
Like the roof in front of this dormer.

 

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Discussion Starter #8
So it looks like a skirt roof on the side of the house but just part of the roof that left in place when they added the dormer. That section does not need venting. :wink2:
Like the roof in front of this dormer.


Exactly like that.
 
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