Van Chocstraw wrote in
:

Robert11 wrote:
Hello,

Live in New England; typical Colonial.
Every few years it seems we get water damage due to "ice dams"

a. exactly what is the mechanism that causes these ?

What conditionsmust be present ?
e.g., temp's at night or during the day, etc. ?

b. We have gutters.
Would it help minimize the possibility of having, if we removed them
?

Any thoughts on this would be most appreciated.

Thanks,
B.


If your attic is uninsulated the house heat rises up and melts the
snow which flows out to the overhang on the roof which is unheated and
the water freezes. So water keeps flowing down and hits the previously
frozen ice at the bottom and pools. If it gets deep enough it back
flows under the shingles and leaks in.
Prevent it by raking off the snow 3 feet above the over hang, insulate
the attic put heat coils on the eves or when you reshingle the roof
put 'ice and water' paper under the shingles half way up the roof.
It's sticky paper that self seals at the edges and sticks to the
roofing material. It water proofs the roof against back flow.


Where do you get "half way up the roof"? That can be overkill and it
could be insufficient.



http://www.graceathome.com/pages/roof_faq.htm#FOURTEEN

"How much Grace Ice & Water Shield do I need for a specific roof pitch?

Grace recommends that the Grace Ice & Water Shield is extended a min. of
24"" beyond the inside face of the exterior wall line of a building and
should extend from the eave above the highest expected ice damn. Check
local codes and regulations as they may vary. If installing full
coverage of Grace Ice & Water Shield, use same roof area calculation for
finished roof covering."