[RE-wrenches] Flashing vs Sealant... again (is sealant code defensible?)

[Ray Walters]

  Hi Glenn;

How do you and the roofers deal with Propanel steel roofs? That's 
hundreds of penetrations for the screws, with no flashings, and they 
depend on just a little rubber gasket.  Or how about the lead head nails 
on a corrugated metal roof?  Roofers themselves make plenty of unflashed 
penetrations by your definition. Instead, I would call those roofing 
attachments, not penetrations.
      If I'm putting a 2 inch hole through a roof, then that constitutes 
a penetration, and using a flashing is usually a good idea.  But when 
I'm filling a 1/4" hole with a 5/16" lag, its really much closer to 
being a roofing attachment than a penetration.
     BTW, we're not just depending on some adhesive to stop the 
moisture.  An L foot is really a 1/4" thick aluminum flashing.  It has 
at least  4 sq in. of surface area held permanently in place by a 
mechanical fastener that is applying a significant amount of downward 
pressure.  Bulkheads on water tanks and boats use the same method, and 
hold not just against moisture intrusion, but moisture under pressure.  
How many PSI can a flashing take?
     With L feet, we're doing less damage to the roof underneath: one 
.05 sq in. hole through the roof, then covered by 80 times its surface 
area with 1/4" aluminum over a roofing approved sealant held 
mechanically under pressure.  With flashings, you are tearing up the 
original roof, separating shingles from each other, ripping out mounting 
nails, tearing the undersides of the shingles, and removing many square 
inches of shingle off the roof, all to install a  200 sq in flashing to 
cover a 0.05 sq in hole. I've done it both ways, and I think you've got 
more of a chance of causing a leak installing flashings, especially on 
an older roof. Flashings make more sense on new construction, when the 
roofer can install the roof over the flashings after.
     The L foot mounting method was developed in the hot water days, and 
predates PV by over a decade.  We've got more proven long term success 
with this mounting method than most module companies today can claim for 
their products  (or makers of the latest flashings for that matter).  
Instead of all this knee jerk: flashing = good, L feet = bad,  how about 
the roofing and solar industries coming up with actual testing to 
determine what mounting methods actually leak, and which ones don't?  
Meanwhile, many on the list have already pointed out: L feet installed 
with the correct sealant have lasted as long as the comp roofs they're 
on, 30 + years.
     Don't get me wrong, I use conventional flashings in many 
situations, especially on flat roofs.  The Chemlink flashing is a 
favorite, but yes, it depends on chemicals to provide the moisture 
barrier, as do most roofing materials ( including comp roofs and most 
commercial flat roofs).
Chemlink Flashing utilizes a 2 part adhesive process.

R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760

On 4/13/2014 7:22 PM, Glenn Burt wrote:
>
> In New York solar installations are required to have all penetrations 
> flashed -- chemical sealant is not flashing. Ask any roofer what he 
> thinks about drilling through the roof and relying on purely a 
> chemical adhesive/sealant for the prevention of water intrusion, and 
> he will laugh at you.
>
> Glenn Burt
>
> One of many inspectors for the NYSERDA PV and Thermal incentive 
> programs...
>
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