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Capn Pete 12-15-2012 12:34 PM

Attic Condensation

I live in a 1913 vintage house of about 1200 sf. The roof is a newer 50 yr comp with a hip on the east end and gable on the west end. Our prevailing winds are 90% from the SW. Our climate is temperate, lots of rain, little snow.

I noticed the other day that there was moisture condensing mostly on the North side, less on the South. I had previously installed approx 8-9 "birdblock" type vents each with 3, 2.5 inch holes. The roofers installed 3 (8"?) can vents near the ridge. There is a west facing gable vent about 12" x 16". 6" of "rock wool type" insulation.

The air in the attic seemed pretty cold, roughly the same temp as outside.

The moisture I saw made the sheeting damp and most protruding nails looking vaguely rusty and had a tiny drop of water on the point. There is no water on the insulation below nor does there seem to be any rot yet.

Inspection revealed that almost all my soffit vents were blocked- clogged screens and insulation. I unblocked all of them and installed 6 more. Many houses in the area don't have any.

Reinspected today (10 days later) and situation is better but still have condensation. I am hoping to get suggestions for fixing....ridgevent?


jagans 12-15-2012 12:53 PM

Hi Cap.

Is this condition only in one spot?

Are there any roof penetrations above this area?

Capn Pete 12-15-2012 02:22 PM

Not just one spot, whole length of roof.

The can vents penetrate the roof, they have considerable moister on them too...

jagans 12-15-2012 03:19 PM

Is your house balloon framed?

jagans 12-15-2012 07:06 PM

Since you did not answer, I will elaborate. Baloon Construction is where the wall studs set on the sole plate and run all the way up to the eaves. The second floor joists sit on a ledger strip that is let into the studs. Most of these homes had rough hewn full cut studs, in other words 2 x 4's were actually a full 2 x 4 inches. In this type of construction, air can flow in between the studs and run right up and out at the top. This results in a chimney effect in the walls, and a lot of hot moist air in the attic. If your home has been insulated this is a moot point. If not the best thing you can do is stuff the cells between the studs in the basement with fiberglass bat to halt convection up between the studs. You are getting warm air up there from somewhere, this may be where.

Capn Pete 12-16-2012 01:27 PM


House is a single story and almost all of the outside walls (80%) now have fiberglass insulation installed by me during previous projects.

I will check and verify there is a top plate.

Windows on Wash 12-16-2012 01:41 PM

Post up a picture of the home.

Google Air Sealing and Insulation and that will get you started on the right path.

jagans 12-16-2012 01:46 PM

Thats OK Pete, Not necessary. It is probable that you are losing hot air into that attic from somewhere. Maybe a drop down set of stairs that isn't tight? A bathroom vent? Recessed lighting fixtures? Leaky Metal Flue? Where do you live? If I could look at your envelope with my IR Camera at night, I could tell you. Your energy provider might have an energy audit service they will provide for a reasonable price.

Capn Pete 12-16-2012 04:13 PM


No drop down stairs, no can fixtures, no other penetrations.....Bathroom vent fan....hummm

I will check this out. Thanks

Windows on Wash 12-16-2012 05:57 PM

Top plates will leak more cumulatively than most of those other things in terms of normal leakage.

If you have a bath fan venting in the attic...that is bad news.

Gary in WA 12-16-2012 11:27 PM

Where are you located?


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