Bad attic airflow and ice daming
clarkster75
| Posted in Energy, Heating & Insulation on
If you have poor airflow in the attic because the insulation was blown into the eaves all the way to the soffett/fascia, and your ridge/roof venting is just average, how much will it help, if you restore good airflow at the eaves, to help stop ice damming? I know there are a lot of variables, but can it help that much?
Does good airflow do more to cure ice damming than roof pitch, ice+water shield, quality of shingles and, well, and heat tape?
Replies
Good airflow in conjunction with good attic insulation can help prevent ice damming. The point of the exercise is to keep the entire roof surface COLD, so that snow will not melt on those parts of the roof over the heat envelope and then run down and freeze into an ice dam on the eaves, which are always cold. Good airflow also contributes to eliminating or reducing condensation frost, which is a separate problem from ice dams.
Depending on a lot of variables--the roof pitch, the exposure, the snow load and average winter temp, and more--you could get away without any supplemental ice-dam prevention. But if you are in a marginal situation, such as a medium-low pitch roof with a southerly exposure and lots of direct sun, you're likely to have some problems and things like ice and water guard or heat tape are designed to either get rid of the pooled water sitting behind the dam or keep it from getting into the house.
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
Good ventillation is probably number 1 in your list. Number zero should be sealing air leakage through the ceiling.
Airflow is mostly a band-aid to clear away warm air that is entering the attic space.
More venting can potentially make matters worse by drawing even more warm air from the structure. ("Stack Effect")
Seal the attic plane first. That will provide the best return for the least cost.
Yeah, but sealing is the hardest, most labor-intensive step. (So it's the one that the builders take the most shortcuts on.)