Attic insulation

This attic has the ceiling insulated with Fiberglass with paper vapor retarder. There is rafter venting between the insulation and roof sheathing. The gable ends have fiberglass with plastic sheeting. The floor (2nd floor ceiling) does not appear to have any insulation (where visible).

The attic doesn’t have its own heating source and, I am assuming, seldomly used as it has pull down stairs (that’s another story) so it technically is not a conditioned space.

I did notice some staining from moisture (not currently wet) on the drywall for the 2nd floor ceiling at the Butt ends of the Batting on the West side of the roof. The staining was noted in atleast 3 bays at the same location of the Butt joints.

Outside of the paper being exposed issue, is the paper holding moisture ie: condensation and then flowing to the joints (I don’t believe there are any issues with the roof. Would it be correct to just install drywall and call it good? or better to remove the paper and leave for free movement of moisture?

As said before, there is rafter venting installed and from the outside there appears to be ridge venting, though could not be confirmed without removing some of the stapled in insulation. Shouldn’t the soffit and ridge venting help alleviate the moisture issue?

Thanks for input,



Even without a heat source, heat from below makes this a conditioned space, and warm air carries more moisture. I suspect air is moving thru the paper retarder, hitting the cold surface of the roof sheathing and causing condensation there. I would install an airtight plastic vapour barrier.

John Kogel

I find this type of installation once in a while.

First and foremost, remove the plastic vapor barrier from the gable end. If any moisture gets behind this plastic, Mold will accumulate.

Then (once you have inspected for proper ventilation) recommend that all this attic insulation get covered with drywall in order to meet current codes requiring vapor retarders to be sealed with gypsum board due to it’s flammable properties.

When drywalling this attic, the insulation behind the knee walls needs to be corrected. The blanket insualation should be removed from the roof rafters and neatly placed into every knee wall stud with the vapor retarder facing towards the living area. Then the floor cavity (behind the knee wall only) needs insulation added.

Upgrading Insulation

Also keep in mind there needs to be an air gap between the layer of insulation and the roof decking, to let the air flow up the roof. Many times the the baffles at the soffit are missing and the insulation is as thick as the rafters. Without this air gap and the ridge vent in every bay there will be problems with condensation.

My illustration #2 identifies the baffles in question.

CONDITIONED SPACE, DIRECTLY – An enclosed space that is provided with heating equipment that has a capacity exceeding 10 Btus/(hr-ft2), or with cooling equipment that has a capacity exceeding 10 Btus/(hr-ft2). An exception is if the heating and cooling equipment is designed and thermostatically controlled to maintain a process environment temperature less than 65 degrees Fahrenheit or greater than 85 degrees Fahrenheit for the whole space the equipment serves. [See California Code of Regulations, Title 24, Section 2- 5302]
CONDITIONED SPACE, INDIRECTLY --Enclosed space that: (1) has a greater area weighted heat transfer coefficient (u-value) between it and directly conditioned spaces than between it and the outdoors or unconditioned space; (2) has air transferred from directly conditioned space moving through it at a rate exceeding three air changes per hour.