[RE-wrenches] The perfect solar ready roof
North Texas Renewable Energy Inc
ntrei at 1scom.net
Fri Oct 22 07:47:03 PDT 2010
Phil hits the nail on the head, it sounds like we've both been down this
road. Problem is it's not always as simple as asking the roofers to do their
job your way when you are not signing their paycheck.
I contracted a metal roof PV installation a few years back but only got the
job on the condition, by the very fastidious homeowner, that I could verify
that the installation won't cause leaks or void the warranty on the <2 year
old roof. He gave me the roofers name and the roofing product and mfgr. I
researched the manufacturers installation requirements for our inland
climate. Then I called the roofer and asked if the 16" wide panels were
installed per the mfgrs specs.
He proceeded to go ballistic, telling me that if I put one module on 'his'
roof he would void the warranty. Even after sending him links to the S5
engineering test results he refused to even talk to me. Finally the customer
had to have a long talk with the guy before he was convinced his roof had
been installed correctly.
Bottom line you cannot ever be certain about the quality of the installation
by someone else. Besides, the homeowners insurance company will have the
last word on whether a PV mounted roof, found across the street after a
windstorm, was installed right or not.
CYA
Jim Duncan
-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org]On Behalf Of Phil
Undercuffler
Sent: Thursday, October 21, 2010 10:29 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] The perfect solar ready roof
There is a big difference between standing seam metal roofs and surface
screwed metal roofs. With surface screwed (aka ProPanel or Ag Panel),
screws penetrate through the roof skin and rely upon a neoprene gasket under
a cupped washer to provide the weather-tight seal. It makes a pretty good
seal and I've used it on my own home, but I don't think I'd use it in
Montana and I sure wouldn't try to attach PV over it. The days of lagging L
feet through the roof deck are thankfully waning, and there is almost no
practical way to use a flashed method of mounting with surface screwed
metal.
With standing seam roofs, the metal is formed into long U shaped pans. As
each pan is installed, the roofer nails L shaped "clips" to the deck with
one side of the clip butted up against the latest pan. The next pan is
butted up against the first, which captures the clip between the two. The
upward facing legs of the U (and clip) are then crimped and folded over,
locking them together and forming a watertight seal. I had a standing seam
roof on my home in Cincinnati -- eighty years old and still going strong.
The biggest challenge with attaching PV to standing seam roofs is not how
well the modules are attached to the skin, but how well the skin is attached
to the structure. Read the archives, but in the end this really comes down
to how close the roofer installed the clips. This is where the 4" that
Andrew mentioned comes into play (seems a little excessive to me, but what
the heck, I'm not a roofing dude and this isn't something you want to do
twice). The dream scenario part comes in when you realize that YOU get to
drive the bus on how closely the clips are installed, as opposed to being
presented with a roof where you have no idea how many clips were used, what
the spacing is, or even whether nails or screws or bubble gum were used to
connect them to the deck. The folks that make the S-5 clamp know metal
roofs, and they can help you determine what spacing works for your
application. Get that into the contract, and make sure someone is on site
providing oversight when the roof is installed.
As far as some of the other options which were presented -- yes, lagging
into engineered I-beams is probably not a good idea without checking with
the manufacturer, but adding a second layer of ply doesn't suddenly make a
structural base for lag screws. Lag screw pull-out resistance is provided
by inches of thread embedded into solid wood, and shiners (fasteners that
poke through the deck into the attic space) won't give any real strength. If
it's really 1/2" ply, adding a layer of 3/4 ply would give you 1-1/4" of
"wood" -- do the math and see if that's enough for your climate. Adding 2x
blocking would be an option if you have access to the attic, but you need to
make sure the loads transfer to the rafters (I-beams), rather than
concentrate on the deck. Nailing the blocking would be fine -- after all,
that's how houses are built. Lagging the blocking as suggested by someone
earlier, however, will not only be insanely difficult but risk splitting the
top chord of the beam. If you split that, I would immediately stop what
you're doing and consult with the I-beam manufacturer. Big liability moment
there.
But I'd avoid all that lags, nails, plywood and blocking entirely, put on
a standing seam metal roof with adequate clips and install the PV with S-5
clamps.
My .02
Phil Undercuffler
On Thu, Oct 21, 2010 at 11:52 AM, benn kilburn <benn at daystarsolar.ca>
wrote:
andrew,
a few comments added to your last email...
You Wrote....
If you ask me this is a dream scenario. The scary thing about S-5!s is
that you rarely know how often the roofing panels are attached to the
decking and how well the decking is attached to the framing. i'm not overly
familiar with standing seam metal roofs (and i know they are not all created
equal) but aren't the screws holding the metal roof panel to the decking
visible at the bottom, at the top under the vent cap and anywhere along the
length of said panel? i agree about the 'unknown' attachments btwn the
decking and the framing In this case you can direct the roofer to fasten
the roof as often as you want. I had a PE do an analysis for a sure-fire
acceptable attachment method for a standing seam roof given: 90 mph wind
zone, 18" wide standing seam roofing panels, flush-mounted PV array (modules
to rail to S-5!s, no tilt legs), and his result was that if the roofing
panels are fastened every 4" along each seam you are in the clear. No
doubt, that seems like quite a few fasteners. He did not address the
decking-to-framing attachment, So worst case scenario, you get a 90+ mph
wind that takes the array, the metal roof and the decking for a ride to the
ground, (HAS ANYONE SEEN OR HAD THIS HAPPEN?) when it is determined that the
decking wasn't properly attached to the framing, who do ya call? PV
installer, PE who stamped it, roofer? I'm not looking for a place to point
fingers, I'm just looking for some insight on this so i understand our
responsibilities a bit better. I realize that it would be onerous to
confirm the number and placement of decking to framing attachments) but
while the roof is off you could add as many fasteners as you want. If the
structure of the roof is in question I would definitely have a PE look at it
and stamp the plans before proceeding, but once you have everything under
the roof robust and approved, you are primed and ready for a worry-free,
penetration-free S-5!-to-standing-seam array install.
In another email string someone mentioned issues with S-5!s slipping
down the roof due to snow which is why I recommend attaching at every seam
and breaking out that torque-wrench when installing.
Good luck!
...end of your msg
in response to Kris' suggestion, don't the 2x6's need to be toe-nailed
into the 'rafters' on either side? or in this case toe-nailed into the
beams? which probably wouldn't be much different than the 'inadvisable' lag
bolting into them.
cheers,
benn
DayStar Renewable Energy Inc.
benn at daystarsolar.ca
780-906-7807
HAVE A SUNNY DAY
----------------------------------------------------------------------------
From: atruitt at gmail.com
Date: Thu, 21 Oct 2010 11:30:40 -0600
To: re-wrenches at lists.re-wrenches.org
Subject: Re: [RE-wrenches] The perfect solar ready roof
If you ask me this is a dream scenario. The scary thing about S-5!s is
that you rarely know how often the roofing panels are attached to the
decking and how well the decking is attached to the framing. In this case
you can direct the roofer to fasten the roof as often as you want. I had a
PE do an analysis for a sure-fire acceptable attachment method for a
standing seam roof given: 90 mph wind zone, 18" wide standing seam roofing
panels, flush-mounted PV array (modules to rail to S-5!s, no tilt legs), and
his result was that if the roofing panels are fastened every 4" along each
seam you are in the clear. He did not address the decking-to-framing
attachment, but while the roof is off you could add as many fasteners as you
want. If the structure of the roof is in question I would definitely have a
PE look at it and stamp the plans before proceeding, but once you have
everything under the roof robust and approved, you are primed and ready for
a worry-free, penetration-free S-5!-to-standing-seam array install.
In another email string someone mentioned issues with S-5!s slipping
down the roof due to snow which is why I recommend attaching at every seam
and breaking out that torque-wrench when installing.
Good luck!
Andrew Truitt
NABCEP Certified PV Installer™ (ID# 032407-66)
Truitt Renewable Energy Consulting
(202) 486-7507
http://www.linkedin.com/pub/andrew-truitt/8/622/713
"Don't get me wrong: I love nuclear energy! It's just that I prefer
fusion to fission. And it just so happens that there's an enormous fusion
reactor safely banked a few million miles from us. It delivers more than we
could ever use in just about 8 minutes. And it's wireless!"
~William McDonough
On Wed, Oct 20, 2010 at 2:32 PM, Kristopher Schmid
<solman at legacysolar.com> wrote:
What about screwing in double 2x6s flush to the roof deck between the
beams where your feet will attach and lag bolting into that? Definitely
check with the beam manufacturer first, though.
Kris
Legacy Solar
864 Clam Falls Trail
Frederic, WI 54837
715-653-4295
solman at legacysolar.com
www.legacysolar.com
-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Scott
McCalmont
Sent: Wednesday, October 20, 2010 12:00 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] The perfect solar ready roof
In general, you shouldn't drill or cut the flanges on engineered
wood beams. I think that eliminates lag screws into the rafters. They
probably wouldn't have the same pull-out strength as a lag screw into a
conventional rafter, either.
Scott
On Oct 19, 2010, at 7:58 PM, Chris Daum wrote:
Dear Wrenches:
I have a composite (shingle) roof at hand, and the owner wants to
upgrade it to a metal roof and install a 5kw+ array on it. The rafters are
those (sort of) particle board I-beams covered with 1/2" plywood (and
shingles). What's the best metal roofing you could suggest--and would you
beef up the wood to lag into?
Thanks for all your input.
Chris Daum
Oasis Montana Inc.
406-777-4309
406-777-0830 fax
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