Attic Ventilation Part II

[MRM]

A while back I asked about attic ventilation (see thread391-115032). I looked into it more and after sealing up the attic entry hatches on both sides (it's a duplex) in 2005, I haven't seen anymore frost on the nails on the underside of the roof sheathing. I've noticed that the seal (garbage bag fully taped to the area around the hatches) are usually "sucked" tight against the hatch. This would indicate a low pressure situation in the attic which tells me that air is probably moving as it should. I also think this went a long way toward solving the moisture problem I had in the attic.

I've redirected my gutters outlets away from the foundation too (they were pointed toward the foundation when we brought the house). Since I've done that, the crawl space seems to be much drier now. Hopefully this would also contribute to a drier attic space too.

Now I've got a more specific question about attic ventilation. I've got a continuous sofit vent on both sides of the roof, and a continuous ridge vent. I've also got a gable vent on either side of the house. I'm beginning to think that if I sealed up the gable vents, then the sofit vent and ridge vent would work even better than they do now. Is is possible for these gable vents to be messing with the natural air flow from the sofit vent to the ridge vent?

I'm trying to correct the ventilation problem and optimize air movement before I tackle the next: there's mold on the underside of the roof sheathing.

 

[MintJulep]

You might want to get a copy of this paper:

Understanding Attic Ventilation

Throughout the balance of this article the terms attic and roof are used interchangeably. In cold climates, the primary purpose of attic or roof ventilation is to maintain a cold roof temperature to control ice dams created by melting snow, and to vent moisture that moves from the conditioned space to the attic. Melted snow, in this case, is caused by heat loss from the conditioned space. The heat loss is typically a combination of air leakage and conductive losses.

AUTHORS: Joseph Lstiburek, Ph.D., P.Eng., Fellow ASHRAE
CITATION: ASHRAE Journal, Vol. 48, No. 4
NO. OF PAGES: 8
PAGES: 36-38, 40, 42-45
PUBLISH DATE: 2006
PUBLISHER: ASHRAE
MEDIUM: Downloadable