Replies

1. GBA Editor
   Martin Holladay | Mar 28, 2017 04:59am | #1

   Wally,
   Several manufacturers sell products that are designed to introduce ventilation air in roofs without overhangs. The product that you linked to can be installed on a retrofit job.

   That said, it's almost always a bad idea to try to solve an ice dam problem with ventilation. That approach almost never works.

   To solve an ice dam problem, you need (a) to seal the air leaks in your ceiling -- usually with a method called blower-door-directed air sealing, and (b) to increase the R-value of your roof or attic insulation, especially near the eaves.

   In most cases, the best fix involves installing one or more layers of thick rigid foam above the roof sheathing. This approach requires the installation of a second layer of roof sheathing above the new rigid foam, as well as new roofing.

   Here are links to several articles to guide you:

   Prevent Ice Dams With Air Sealing and Insulation

   Ice Dam Basics

   How to Install Rigid Foam On Top of Roof Sheathing

   -- Martin Holladay

2. 
   seabornman | Mar 28, 2017 04:09pm | #2

   I have been successful in getting rid of ice dams and icicles on two houses I have owned that have not had opportunity for soffit vents; both were in snow country. Although the two houses were much different in construction (one timber framed and one "standard" ranch house), the basic premise was the same: reduce air movement from the house into the attic, and add lots of insulation. In the house with "standard" construction I found all of the penetrations of wiring, vent pipes, and boiler flue and sealed them with caulking and sheetmetal when needed. Attention to detail is critical. The only ventilation to the attic on that house were two tiny gable vents and a poorly-installed ridge vent.