attic insulation--no soffit vents

Old 07-27-03, 10:15 AM
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attic insulation--no soffit vents

My house was built in 1926. It is two stories tall plus a full walk-up attic with an 8' ceiling. The attic floor is insulated. The previous owner had fiberglass insulation installed in the walls/ceiling a couple of years ago but by the time we bought the house, last winter, there was already mold forming in the insulation. (It was fiberglass insulation covered with plastic sheeting.) We ripped it all out last week when we were having the roof replaced. The roofer said the mold problem was because that the attic wasn't vented. We had a ridge vent installed. Now I want to replace the insulation without getting more mold... I thought there were soffit vents because it looks like they are there from the outside, but I got on my belly and dug through a couple of feet of the blown-in floor insulation along the periphery of the attic thinking that the vents were covered by the insulation. Lo, and behold, when I hit what I assume is the top side of the soffits there are no vents, just solid wood.
Long explanation, I know. Now the question, can I just put new fiberglass insulation in, cover it with plastic again, and assume that the new ridge vent is all the venting I need? If not, what do I have to do?
And, while I'm at it, once I solve the venting problem and get around to putting the new insulation in...should I do anything to the wood before I cover it up--like try to disinfect it or something? You can still see spots of mold on the wood.
P.S. This is Minnesota--cold climate and prone to ice dams!
Old 07-27-03, 11:11 AM
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The ventilation in your attic works by drawing air in through the soffit vents and exhausting it through the ridge vent using the chimney effect. The moving air keeps the roof deck cold so snow doesn't melt causing ice dams, and it removes any moisture that leaks into the attic from the heated space. In order for the ventilation to work properly you need both ridge and soffit vents and a clear path between them. The net area of the soffit vents should equal or slightly exceed the net area of the ridge vent. Use styrofoam baffles to prevent insulation from blocking the soffit vents.

Wash the moldy areas with bleach and let dry completely before reinsulating. Consider using cellulose loose fill instead of fiberglass when you reinsulate. It packs tighter than fiberglass and will form an air barrier that reduces the amount of hot moist air escaping into the attic.
Old 07-27-03, 07:52 PM
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You description is good but I need more information. What I can deduce from it is the attic floor is insulated, the soffit vents are attached to solid wood, you had a ridge vent installed and the former owner put insulation in the walls and ceiling and covered that with plastic. It is apparent that sheet rock was not installed over the plastic and I can deduce from that, that the attic is not heated.

If this is the case, then remove the insulation from the walls and ceiling in the attic. Remove the soffit vents and cut holes in the wood to allow air flow. And that's it. Do not insulate the walls and ceiling of an unconditioned space (attic). If and when you decide that you want to heat this area, then install styrofoam baffles up against the underside of the roof, install insulation against that and then sheet rock.
Old 11-02-03, 07:27 AM
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A vapor barrier such as plastic sheeting should be between the house occupants and the insulation. It sounds like the sheeting was between the insulation and the atmosphere.

So, it is/was locking in the moisture, instead of preventing it from entering an area where it could condense.

Typical construction 'sandwich' is this:

Vapor barrier
Exterior of building

Sometimes the paint is formulated as the vapor barrier, which is theoretically perfect, but the practical need is to place the barrier at the point before possible condensation of water vapor.
Old 11-02-03, 08:21 AM
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Some homes do not have soffits, like my old rental. It does not have an overhang and nowhere to put soffits. I have plenty of vents at top and as many vents on the lower sides. It has only been there since 1944 and no problems. In my case I added insulation and did the best I could with the venting.

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