Black Plywood

[allseason]

This is in the attic of a circa 1960's ranch. Multiple layers of composition shingle over plywood. The underside of the decking at the rear roof with northern exposure is stained black. more so toward the eaves. The south side is relatively clean. Any idea on what would cause this? First pic is south side, second is north side.

Click to Enlarge

44.97 KB

Click to Enlarge

52.43 KB

[AHI in AR]

Condensation. North-facing side stays colder. Coldest areas are low near eaves.

[hausdok]

Hee, hee,

Stained black, you say? If that's black I'd hate to see what would happen to your senses after a few Northwest attics. I can hear ya now, "Somebody help me, I'm blind, I'm blind!"

ONE TEAM - ONE FIGHT!!!

Mike

[John Kogel]

Play fair, Mike. There is black around the nails, North and South.

The South-facing side warms up a bit in the sun, just enough to dry the wood out or reduce the amount of condensation.

The cause is usually warm moist indoor air leaking in to a cool attic space.

[kurt]

Originally posted by John Kogel

The cause is usually always warm moist indoor air leaking in to a cool attic space.

That's what I think, anyways.....

[Tom Raymond]

The good news is that the fix is cheap. A foot of cellulose will triple the R-value, affect enough air sealing to prevent any further condensation and staining, and present an adequate phisical barrier to keep all but the nosiest homeowners out of the attic. The vast majority of our cells jobs are under $2K.

[kurt]

I'm a believer. The jobs we've done where a cheap layer of cells is applied all magically improve and the problems go away.

I remember when we all thought the stuff was crap because it compressed. Who'da thought in 1982 that was a benefit?