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carbonater

07:21AM | 09/02/03
Member Since: 08/31/03
9 lifetime posts
Bvroofing
Hi. I have a 20-27ft family room w/13ft cathedral cieling. the bottem 4 ft of roof gets no sun. when snow melts and runs down it refreezes and causes ice dams. I have installed elect. deiceing cable and it works ok but, I am looking at a Rain Dispersal system to lower elect. usage. Any thoughts?

pgriz

01:56PM | 09/02/03
Member Since: 01/21/03
67 lifetime posts
99% of time the ice dam means insufficient insulation and ventilation. If you want to stop heating the outdoors, with the heating cables and the heat loss from the roof, look into improving both insulation and ventilation. Depending on your home's construction, you may have enough room in the cathedral ceiling portion to do that. As well, if you install a slippery surface (like a metal roof), the snow will slide off and less of it will remain to make an ice dam. Of course, you also have to make sure the sliding snow does not create its own problems, as in falling on someone or something!

k2

06:30PM | 09/02/03
Member Since: 06/06/03
1250 lifetime posts
Excellent post, pgriz says it all! Figure out the ventilation & insulation; "double-bonus points" for a slippery roof...good luck.

carbonater

10:00AM | 09/03/03
Member Since: 08/31/03
9 lifetime posts
Ceiling is 16"with 14" r-38 oc insulation. Leaving A 2" air gap for air movement from soffit vents to a ridge vent. Any other ideas?

pgriz

11:12AM | 09/03/03
Member Since: 01/21/03
67 lifetime posts
The 2" air gap may not be enough if you already have it and you are still getting ice damming. A 4" air gap would be much better. One way to get more air space is to replace your current insulation with rigid panel insulation. Owen Corning makes various panels which claim an R-10 value for two inches of thickness. Other manufacturers have similar products. Four such panels would then give you R-40 insulation, and eight inches of air space.

If you are going to go to the trouble of installing new insulation, you also want to check that the air channel from the soffits is not obstructed. We find that the space above the vented soffits is often obstructed by solid wood, or by blown-in insulation.

carbonater

09:07AM | 09/04/03
Member Since: 08/31/03
9 lifetime posts
This is a cathedral ceiling. no access to insul. without tearing out roof or cieling. Do you think the prob. is insul. even though sun melts snow above 4' and refreezes at bottom where there is no sun? Has anybody used a Rain Dispersal system?

pgriz

05:30PM | 09/11/03
Member Since: 01/21/03
67 lifetime posts
If the only source of the heat creating the meltwater is the sun and none from the house, then the solution I proposed to you won't help. In that case, cables are about the only thing you can use. However, in almost every case when I've inspected roofs to determine the causes for ice dams, the problem was insufficient insulation and ventilation.

You are also right in observing that the only way to change the insulation in your roof is to go either through the ceiling or the roof. So if you believe that the cure is worst than the problem, it looks like heating cables are the current solution for you.

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