Roof Valley Leaks Ice Dams

Jim Fiste is getting ready to reroof his home in Cedarburg, WI. Let him fill you in with the details:

"I have a roof valley that is formed by two intersecting cathedral ceilings. Both ceilings have ridge vents and 2' vented overhangs.  However the portion of the valley above the overhang only has venting at the ridge vent.  This causes major ice jamming and ice dams.

I currently roof rake but even that is sometimes not enough.  I will replacing my roof shortly. Is there anything I can do at that time to help this problem."

You can clearly see the valley in this photo. It's easy to stop ice dam leaks. Photo credit: Jim Fiste

Here's my answer:

Jim, the ice dams and jamming don't really have much to do with the ventilation you point out. It's all about the heat escaping from the interior of your home right where the ceilings pass over the outside walls. The insulation is thin in these places and the infrared radiation melts the snowpack.

The only way to STOP ice dams is to remove the fuel that creates them. This means raking off the snow. That can be a PIA and a chore, but in your case it's doable because it appears you can reach these roof surfaces from the patio somewhat easily.

But if I were you, I'd have the roofer install Grace Ice and Watershield in the valley and on either side of the valley up to the wood siding. You want the membrane to extend at least 6 feet up from the gutter.

This membrane is made to prevent and STOP the leaks created by ice dams.