[RE-wrenches] The perfect solar ready roof

Thu Oct 21 20:29:27 PDT 2010

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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