Ice chunks crash down on lower roof

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Old 03-01-16, 04:30 PM
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Ice chunks crash down on lower roof

My house has a large second floor dormer with an almost flat roof section. The first floor extends out beyond the dormer wall with an additional pitched roof section.

During the winter, ice chunks, some large, slide off the dormer roof and crash down on the first floor roof section below. There is some shingle damage. There is no attic or crawl space just under the dormer roof and some ice dam problems up there but that is another program.

This is an older house and the ceiling insulation is far below modern standards. It would be necessary to rip open the second floor ceiling to do anything with the insulation.

Related question: The entire roof is scheduled to be redone including new shingles. Is it a good idea to put a layer of rigid insulation on top of the existing nearly flat roof section and put the new roofing (perhaps EPDM rubber) on top of that?

The diagram shows a cross section of the house.
 
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Old 03-01-16, 05:35 PM
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Hi Allan,
Below is some related reading. But yes, they do use rigid on top of the sheathing. Detailing the fascia and rake to accommodate the insulation requires some planning and I've seen more articles on that issue. A large nursing home next in Bangor just added about 6" of rigid (two layers) over their sheathing (sloped roof). That was a 6 figure project for sure.

Another approach you might consider since you are replacing the shingles would be to install new rafters from peak to an extended overhang over the problem edge. You could also make some ventilation changes to reduce or eliminate the ice issue, but rain and any ice that does show up would fall beyond the first floor. I have a low slow section of roof on the back of my cape that was dumping rain and some ice onto my bay window so I extended my roof 2" and improved the ventilation and problem solved.

You probably have windows that would be blocked by a 4' extension, so eliminating the ice issue may be the top priority. Does that flat section have ventilation from eaves to the attic above?

Bud
How to Install Rigid Foam On Top of Roof Sheathing | GreenBuildingAdvisor.com
 
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Old 03-01-16, 06:08 PM
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If you are having the roof redone with epdm anyway you could also consider having them build a Dutch gutter, with the runoff sloped to a scupper or drain. Heating cables would be a good idea for that roof either way.

Example of a Dutch gutter: (thanks to MiamiCuse for the link to the image) http://s173.photobucket.com/user/143...onfig.jpg.html
 
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Old 03-10-16, 07:16 AM
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Thanks for the idea. I also need to take into account possible ice dam problems either at the edge or further back where the steeper sloped roof begins.

There is no eave ventilation under the "flat" section. The second floor ceiling is right up against the roof with perhaps 6 inches of insulation.
 
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