William, By gravity flashing i mean one of a bunch of newer systems that provide a metal flashing overtop of the foot. The idea is to have it work like a shingle, where gravity is on your side, not just sealants.
But here in lies the debate for me. A gravity is a nice backup, cause water always goes downhill, right? Well not always, in ice dams, water often goes uphill. There is a real question as to whether a modern sealant system is better or worse than a flashing. I'd like to see data. thanks, Troy Harvey --------------------- Principal Engineer Heliocentric 801-453-9434 tahar...@heliocentric.org On Nov 13, 2012, at 5:51 PM, William Miller <will...@millersolar.com> wrote: > Troy: > > I do not know what a gravity flashing is. Can you elucidate? > > If you have adequate upload mounting strength and need more download support, > you can consider using additional L-fee that simply rest on the shingles > without penetrating the roof. We do that sometimes to take the sag out of > some DPW racking products if the span is long. This should be an easy way to > provide more snow load support. The caveat is that, on pitched roofs, the > resting feet do not provide any support down pitch. > > William Miller > > At 08:04 AM 11/13/2012, you wrote: >> Hi all, >> >> We have been doing PV installs for years with L-feet and silicone without >> problems ever. Even still, gravity flashings seem attractive in shingle >> roofs, to provide a second level of security, and a more professional >> install (at least in perception). But the cost of these systems in >> significant in high snow load areas where we often have L-feet every 2 feet >> on center, to evenly load the structure below. In todays costs, the feet >> could cost as much as 33% of the panel value. >> >> I'm wondering what other people are doing in high snow load areas? >> >> Also. I have noticed that there is a flip side to the risks. We have found >> that unless you have good quality shingles, on a preexisting roof, that >> sometimes the adhesive sticking the shingles together is stronger than the >> low quality shingles themselves - adding risk of trying to shoe horn >> flashing in after the fact. Your experience? >> >> thanks, >> >> Troy Harvey > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@lists.re-wrenches.org > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org >
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