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Old 09-18-2009, 12:51 AM   #1
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Shaky floor


Hi,

I live in an approximately 50 year old house. The floor joists are 16" apart. I have a crawl space. Last winter, we put faced batts in between the floor joists and a thick plastic to keep moisture away from the insulation and floor.

It seems the floor has gotten shakier since adding the insulation. Could moisture be trapped between the insulation and the subfloor causing the shakiness? I have gone down there and the wood did not feel moist, but I don't know why the floor seems so shaky now. Even my three year old daughter walking across the floor can make objects across the room wiggle!

Any ideas? The return vents are in the crawl space too and there are places in the floor you can step to make those echo pretty bad, too.

The floor does not seem to be soft though, just shaky.

Thanks!!

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Old 09-18-2009, 07:04 AM   #2
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Shaky floor


I hope that the plastic sheeting is down on the dirt in the crawl space and not stapled to the underside of the floor joists. Any vapor retarder, like plastic sheet needs to be as close to the warm in winter side of the living space as possible. You didn't remove any blocking or bridging from between the joists to put in the batts, did you?

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Old 09-18-2009, 07:08 AM   #3
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Shaky floor


Faced or unfaced insulation?
If faced the facing should be installed towards the heating space

Dirt floor or concrete?
If dirt the plastic should be on the dirt to prevent water/water vapor from entering the crawl space
Is the perimeter of the crawl space insulated?
Water pipes located in the crawl space ?
Are the returns pulling air from the crawl space?

Insulation does add weight to the floor
What size are the joista & how far do they span?
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Old 09-18-2009, 10:44 AM   #4
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Shaky floor


What do you mean by shaky? Do you mean bouncy, as in the floor deflects up and down as you walk on it? Or does it feel like the structure is shifting side to side?

I wonder if all your moisture-prevention efforts have caused your structure to dry out more than it used to.

Maybe get someone to walk on the floor while you're in the crawl space and look to see if it looks like the subfloor is coming up off the joists.

I wouldn't be surprised if the echoing is just a function of the insulation surrounding the ductwork.
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Old 09-18-2009, 12:44 PM   #5
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Shaky floor


Sounds like the moisture was going to the floor joists making them heavier because they held water. As others said, now dry they feel lighter, shakier, springier, looser. Insulation weighs .9# per cubic foot. With joists 16"o.c., and 2x10 joists with a 15' span = -15 pounds per joist rated to carry 600 pounds each, this would make it heavier not lighter.
You might try slipping some batts on the top of the duct-work to help silence the echo. Did you use stiff wire to pressure fit holding up the batts or string woven back and forth? A solid wood (1x4) may tie the joist bottoms together the take up some of the shakiness, every 4'o.c.
Be safe, Gary
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Old 09-18-2009, 01:01 PM   #6
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Shaky floor


So the insulation is faced, double sided faced, so the faces are on the underside of the sub-floor and facing the plastic sheeting. The sheeting is in between the insulation and the ground. Between the plastic sheeting and the ground, there is about 3 feet of space. The floor of the crawl space is dirt. It is moist down there...it used to flood, but I have since installed a French drain and tuckpointed and now it is just moist down there. Because it did flood this spring before the French drain was installed, the plastic sheeting that was covering the dirt was removed. I guess I will need to put that back down. That way any moisture that is rising up won't get stuck on the sub-floor side of the batted insulation...that is what I worry about...leading to wood rot. That is my main concern. Anybody think that's what is happening or does the batted insulation provide a good barrier for moisture to collect between the sub-floor and the insulation? I went down there and in an exposed area, the wood did not feel moist.

By shaky, I mean like looseish floorboards. Not any swaying or swinging. There are pipes in the crawl space, and the return air ducts, too. The ducts are what is echoing.

I will likely go down and look but since there is insulation and sheeting attached to the subfloro down there, it will be hard to see anything without some destruction.
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Old 09-21-2009, 02:09 PM   #7
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Shaky floor


The situation you have now is that with the insulation having a facer and the plastic sheeting, you have two vapor retarders. The most efficient one, the plastic sheet, is on the cold side of the joists. Any warm, moisture laden air that penetrates into the system from the interior will reach the plastic and condense. This will lead to wood rot faster than no vapor retarder at all. The vapor retarder being close to the warm in winter side of the insulation system will never cause a moisture issue, because it will be kept warm and above dew point. The plastic sheet needs to be on the floor of the crawl space, down at the dirt to prevent any additonal moisture from becoming airborne. Any moisture that condenses down there is not an issue. The space between the dirt floor and the bottom of the insulation either has to be conditioned to prevent condensation or vented. It's hard to say what may be causing any floor vibration or spring if you have some kind of moisture imbalance in the wooden structural components. If the insulation batts are double faced, they have a top and bottom or an interior, exterior side. That is so that the effective vapor retarder is placed in the appropriate direction,(warm in winter).

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