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Old 12-21-2010, 01:00 PM   #1
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Damp Insulation in Attic


We just purchased our first new house about a month ago. The house was finished in November and so far, things have been good.

I was up in the attic last night running another coax cable, and I noticed that the pink fiberglass blown in insulation had a damp feel to it. It wasn't wet, it just felt damp. It also wasn't in one spot either; it pretty much was equally damp throughout the attic. I couldn't see any evidence of drips, and there was no condensation anywhere on the trusses, underside of the plywood roofing deck, or on any metal objects up there. There is also no vapor barrier. Basically, it goes room -> drywall -> insulation.

I forget exactly what the R value is, but I would *guess* that there might be 13" or so of insulation blown in up there and I know it's fiberglass. We also live outside of Chicago so the weather has been pretty chilly lately (20 to 35 degrees). It was also cold up in the attic. I noticed that on the outside edge (where the soffits are), there are vents going down to the soffit. It almost looks like pieces of siding (but it isn't). I also have a ridge vent that runs along the complete ridge of the roof.

My question is...is it normal to have damp insulation in the attic? I use to live in an *old* house with rock wool for insulation, and I remember going up there and seeing water drip from the nails that poked through the decking. Being that it's new construction, I just wanted to make sure that having the insulation a little damp is normal/alright. My other hunch (if it isn't) is that the wood is still damp and drying out being that it's new, and that might attribute to the damp insulation up there.

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Old 12-22-2010, 09:44 PM   #2
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Try and get a humidity reading from the attic. How long ago was the insulation blown in?
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Old 12-22-2010, 10:25 PM   #3
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A, "damp feel" doesn't mean it has an overly high moisture content. Get an actual moisture content and work from there.
Where do the bath fans exhaust?
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Old 12-23-2010, 08:42 AM   #4
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The insulation was blown in...my guess, would be october-ish.

I think the last poster had the best advice. Who knows, maybe it's just me "thinking" that it's wet, while it's only just cold.

All exhaust fans are exhausted <?> to the outside. I learned not to exhaust them into the attic in our first house. All the fans are connected to the pipe (nothing slipped off), and everything else looks fine.

You know, it's probably me just being ultra paranoid , but I think the best test is a device to measure moisture (or humidity).

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Old 12-23-2010, 09:15 AM   #5
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Its highly likely to be condensation and to give it its correct name 'interstitial condensation' and the main cause is that you do not have a vapour barrier on the warm side of the construction, i.e. drywall, vapour barrier, insulation.

Fibreglass has relatively good thermal insulation properties, but when it comes to vapour its not so good!

You have two options:
1. overclad the existing drywall with a plasterboard with either a foil or polythene backing each have excellent vapour resistivities, what you are trying to do is keep the warm moisture laden air on the warm side of the construction, as the air cools it reaches its dew point and becomes saturated and condensation both surface and interstitial are deposited.
The reason you do not notice the condensation on the timber is for the simple reason that it gets absorbed, whereas the fibreglass is glass threads and is unable to absorb the moisture.

Foil has the additional benefit in reflecting back some of the IR radiation; or
2. remove fibreglass insulation material, fit a vapour barrier and then refit insulation material.

Maybe not quite as simple as they sound, but either one would improve your situation.

There is one other solution and that is to 'do nothing' that is until the situation becomes intolerable. The condensation will affect the performance of the insulation material especially in winter months when the condensation will be at its worst, but the choice of what to do is a decision that you will need to make.

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Old 12-23-2010, 10:32 AM   #6
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Sounds like there may be excessive air-leakage into the attic from conditioned spaces below.

1) Is there any HVAC equipment or ducting in the attic?

2) Does it appear that an attempt at air sealing has been made at top-floor wall-ceiling junctions?

Home Inspections, Infrared (Thermal Imaging) Leak Identification and Inspection Services, Roof, Attic, Building, Basement and Foundation Moisture Intrusion and Water Leak Inspections, Troubled Building Consultations - Serving Chicago and Suburbs http://paragoninspects.com/
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Old 12-24-2010, 12:16 AM   #7
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I'm w/ MT. A true vapor barrier is probably not necessary, and could be harmful, depending on where you live (it is always useful to note that when you post). VB's and air conditioning don't mix well, for ex. Air sealing is critical, and a vapor RETARDER. Do the best you can to retro the air sealing; around any penetrations, like pipes and wires, caulk the bottom of the sheet rock/floor joint, if accessible, etc. Ideally, if you can't fix this the easy way, the sheet rock should come off and start over. Water up there is going to do nothing but cause more and more damage.
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