[RE-wrenches] Roof flashings on L-feet in high snow load conditions

[Troy Harvey]

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
taharvey at heliocentric.org



On Nov 13, 2012, at 5:51 PM, William Miller <william at 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
> 
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