Old 06-07-15, 01:07 PM
Thread Starter
Join Date: Aug 2010
Location: USA
Posts: 335

I have a two story house and the second story has 3/4" plywood as decking. It is carpeted with regular carpet and padding. Anyway, my AC has had a hard time keeping up. It can't really hold 80 degrees if its 90 outside. The temperature differential is fine and the AC is working as it should. I thought it was my insulation but I have noticed when the outside humidity is high, it only take mere minutes for the inside to get humid if the AC is shut off. Moreover, if you turn the AC off, the inside temp will go up 5 degrees in 15 minutes or less.

Behind my kneewalls I was doing some looking and noticed quite a bit of cool air coming between the joints in teh decking. Basically, my AC is leaking through the carpet, through the decking and into the second story floor and then travelling out the soffits or to behind the kneewall. Its enough to feel with your hand. wonder there is an "AC Problem".

What is the best way to solve this? Can you pull the carpet and 'seal' the decking with something so no air can pass?

Thoughts? Im not sure how other homes are constructed to combat this, or if they just put in a larger AC system.

Advice needed.
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Old 06-08-15, 04:18 PM
Join Date: Aug 2009
Location: USA
Posts: 4,941
We will need a lot more information about your house. The problem with the temperature rise is only with the second floor or for the entire house? What is the age of the home? How many sq ft is it? How big is the a/c?
Old 06-08-15, 05:35 PM
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Join Date: Oct 2012
Location: Northern NJ - USA
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Not only do you have A/C leaking out you have heat leaking in.

The backside of the kneewall should be insulated as well as the floor joist almost out to the soffet. The back side of the kneewall is a cold zone.

In several houses I'm working in now.... they used blown in cellulose to fill the area between the joists and under the floor.
Old 06-22-15, 09:07 AM
Thread Starter
Join Date: Aug 2010
Location: USA
Posts: 335
2 ton system. 1350 square feet is the area it services. About half of the area on this part of the second story is over an open carport below. The floor is insulated, but not much. The joists are blocked every so many feet. I know this because I cannot run electrical in the floor due to it. I know the kneewall is an issue, but Im trying to figured out how the AC gets through the pad and through the floor.

The floor cannot be insulated any more than it is as it is all complete and closed up. I have a stairwell that leads to the outside on the 'end' of this living space. Under than stairwell is a storage room with two fridges/deep freezes. I know the AC is coming through the floor or the stairwell at least because that room is almost always 78 degrees, even if its 100 degrees outside. Its not a big deal there because that room is sealed to the outside, but if its coming through my floor, its also heading out the soffits too. Im not even sure how to address that since my kneewall storages are decked. I cannot access those joists to seal anything.

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