Ventilated Floor Joists


  #1  
Old 10-20-13, 05:10 PM
R
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Ventilated Floor Joists

Not sure if this is the correct forum for this question, but it appeared to be the closest to my situation.

My house is a two story home with the main living area on the second floor, and a two car garage directly underneath the kitchen and living room at the front of the house. The front and rear of the second story was built with an overhang of about 30" over first story, and on the underside of the overhang there are vents cut into the structure between the floor joists to, what I assume, is to allow ventilation of the floor joists.

There was never any insulation installed in these floor joists but I now want to install some as the floors above can get quite cold. My question is do I really need these vents in the overhangs? I'd really like to close them off as I'm not sure what purpose they would serve once I fill the spaces with insulation.

I've attached a picture showing the vents for clarification.

Thanks...Randy

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  #2  
Old 10-20-13, 05:39 PM
B
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Hi Randy,
The winter time reason for vents is to remove moisture (warm humid air) before it can condense on colder surfaces. As long as those cavities are sealed so there is no air flow from inside to outside, there will be very little moisture transported into those cavities. Essentially, it will be treated like a 30" wall section, air sealed and filled with insulation. My preference is Roxul, a dense mineral wool.

If the interior space is heated and you want warmer floors above, leave a space above the insulation for that warm air to reach. Insulate the outer rim to keep the warm moist air from reaching the colder surface. The space sacrifices a bit of r-value, but provides a heat source otherwise lacking from above. Hard to get the heat from above down to floor level.

Bud
 
 

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