# Attic ventilation help knee walls vented to where?



## tabatt07 (Apr 18, 2010)

My newly purchased house was built in 1903. I would like to add more insulation in the attic but don't want to proceed until I've figured out the ventilation. Can anybody help synthesize this information? What else do I need to consider/look for?

1. There doesn't appear to be any history of water damage or mold. 
2. Not sure the style of house but it's sort of like an A-frame in that the roof is basically a 45 degree angle (1:1 pitch). The orientation is north-south. Note that the porch is unheated space (see pictures) 
3. The third story is the unfinished attic space. The second story is living space with knee walls. The exception is a dormer in the southeast corner bedroom. 
4. A visual inspection from inside the attic and from the ground shows no ventilation on the south side. But see #8 below. 
5. On the north side, I can see vents in the knee wall part of the roof (see pix). From inside the attic, it appears there is insulation stuffed inside the knee wall--I dug in a little but never came close to seeing daylight. There are two roof vents on the north side near the ridge (roughly 1 sf each).
6. Each gable has an inoperable single pane window. They appear to be fairly leaky with some gaps to the outside in the framing. 
7. At each gable there is something happening near where the roof and trim meet. The materials are separating thereby creating an opening into the attic. It's pretty narrow but I can clearly see daylight from inside (see pictures 3 and 4 (measuring tape being pushed through the gap)).
8. On the south side there are a couple of places where I can see daylight when I'm inside the attic. It doesn't appear to be by design but rather a flaw in the way the dormer intersects the roof. 

Again, I'd like to blow in more insulation (I live in Chicago area). It seems like addressing any venting issues should be done before insulation. Thanks for your time.


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## Yoyizit (Jul 11, 2008)

IIRC you should have 5 to 60 Air Changes per Hour with average being around 10. 
You can use mensuration formulas to figure the volume of your space to be ventilated and so then figure the CFM req'd. With your roof design it should be easy.


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## tabatt07 (Apr 18, 2010)

Thanks for the response. I knew an attic fan was one possibility. Is there anything else I should consider in my situation.


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## shazapple (Jun 30, 2011)

Powered attic ventilation is a waste of time and money. They often pull conditioned air from the living space. Typical attic ventilation is 1sqft per every 300sqft of ceiling space on your 2nd floor. It would be split 50/50 between intake ( vents in your knee wall area) and exhaust (vents in your 3rd floor attic space). 

Ideally you have an intake and an exhaust. Intake is usually in the form of a soffit vent, but it does not look like you have any (the holes in your second picture appears to just be the top of the vinyl siding). I assume the knee area gives you access to the south/north facing wall? You may be able to cut holes into that to provide intake. The best product to use here would be continuous soffit venting, as the round vents don't provide much ventilation.
Is there a path for the air from the knee area to the 3rd floor attic? I assume there is some sort of sloped ceiling in your 2nd floor? typically foam baffles are used here to provide the airflow from the knee areas to the attic. 
In the 3rd floor attic you will need an exhaust, which is typically a ridge vent or gravity vent (square vents that look like an upside down cake pan on the roof, which is sounds like you already have two of). A ridge vent would be fairly simple to install yourself. 

I'm guessing the single pane windows used to be gable end vents, which were changed to glass for whatever reason. You could change them back into vents if you don't do the method mentioned above, but they would not be as effective.


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