Replies

1. 
   Dinosaur | Jul 26, 2004 07:52am | #1

   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?

2. 
   DanH | Jul 26, 2004 04:40pm | #2

   Good ventillation is probably number 1 in your list. Number zero should be sealing air leakage through the ceiling.

3. 
   csnow | Jul 26, 2004 07:29pm | #3

   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.

1. 
   DanH | Jul 26, 2004 07:30pm | #4

   Yeah, but sealing is the hardest, most labor-intensive step. (So it's the one that the builders take the most shortcuts on.)