Wet insulation?

[Robert Jones]

Had a multi-family building inspection this morning. Temperature was about 25 degrees. The underside of the sheathing was frosted over in the attic cavity. What was strange, for me anyway, was that all of the loose fill fiberglass insulation felt "wet". Can't say that i have ever run into this. The ventilation was good. Looking at the color of the insulation, which was originally white, it appears mildewy(sp?). Has anyone run in to this?

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[kurt]

All the time this time of year. Ventilation is "good", but as we know, ventilation spec's are completely random, so my take is it's not so good. Add a house that's not air sealed, and you've got a humidor up there.

The insulation is hitting dew point just like the plywood, isn't it?

[Robert Jones]

It is Kurt. Front of the building facing north. Open soffits and ridge cans for ventilation.

[Marc]

Speaking of the worthiness of ventilation specs, my last inspection was a common situation where a pier home was later enveloped with brick veneer on it's own separate foundation. Homes like these are plagued with issues involving elevated humidity in the crawl.

What I found on this one is that 90% of the structural floor (subfloor and joists) had been replaced because of dry rot, despite ventilation openings well in excess of the guidelines. With this one experience, my trust in ventilation guidelines of any sort dropped a couple notches.

I'm glad I'm not in a profession where the cart is ahead of the horse, where I'm supposed to let a book tell me what my eyes are seeing.

Marc

[kurt]

Read the history of how ventilation specs were developed. Completely random all the way from 1930. There's either a ridiculous amount of moisture in the house (which I'd guess you'd see), or the ventilation isn't adequate.

If the plywood is blackened and it's all ice, I don't see how ventilation is adequate.

Honestly, I don't think it's that big a deal, but I'd put it in the report.

[Steven Hockstein]

Could it be due to the bathroom vents? Many multi family buildings have interior bathrooms that require mechanical ventilation. Sometime the ducts don't make it past the attic.

[kurt]

Could it be due to the bathroom vents? Many multi family buildings have interior bathrooms that require mechanical ventilation. Sometime the ducts don't make it past the attic.

Good point. Could be the building has mechanical bath ventilation and it's screwed up.

I overlooked the multi-family aspect. Could be someone else in the building has ridiculous moisture issues effecting the entire building and it's showing up in the attic.

[Jim Katen]

I've pretty much come to the conclusion that most moisture problems in attics have nothing to do with the ventilation of the attic. Instead, they have to do with excessive moisture inside the living space, poor ventilation inside the living space (which is much the same thing), and poor barriers between the living space and the attic.

If a building is pumping its warm, moist air into an unconditioned attic, adding more attic vents rarely solves the problem. No matter how much ventilation you add, there will always be stagnant spots where moisture will condense.

[kurt]

Probably most accurate. Multi family always ups the ante for problems.

[John Kogel]

Prime suspects - Loose uninsulated attic hatch, leaking bath fan(s), leaky pot light housings, range hood leaks, top wall plates with leaky vapor barrier, regular light fixture leaks, in roughly that order.

Old folks tend to overheat their condos and blow a lot of warm air up the stairwell.

At the top of a stairwell especially, I would like to see more often a double layer of drywall for the hatch or drywall screwed to a heavy chunk of plywood, with a good weatherstrip gasket.

Damp air entering at the soffit vents is also possible, but not that common IMO.