Uplift Wind Loading Values [RE-wrenches]

[Tom Lane, Energy Conservation Services]

not good idea to lag into plywood --especially if the collectors are raised
on standoffs--always  attach  to trusses  if possible  --ONE SERIOUS PROBLEM
newer homes being built today do not use plywood on the trusses --but use
OSB board comely call wafer board or particle board made of glue and wood
chips NO WHERE NEAR THE HOLDING STRENGTH OF PLYWOOD -- the  old days of
quality five  eights plywood with five laminates is long past to this cheap
OSB board   gator tom----- Original Message -----
From: "Joel Davidson" <joeldavidson at earthlink.net>
To: <RE-wrenches at topica.com>
Sent: Saturday, March 22, 2003 7:17 PM
Subject: Re: Uplift Wind Loading Values [RE-wrenches]


> Jeff,
>
> In 1994, SMUD was the world's biggest PV customer. The challenge was to
design
> and install the lowest cost grid-tied PV systems in the world on multiple
sites.
> Siemens Solar and other bidders had little or no construction experience.
I knew
> that just about anything could be fastened to plywood if enough screws are
used.
> I discussed my design with an American Plywood Association engineer and
then I
> paid a registered engineer to review my design. We installed over one
hundred 4
> kW PV systems on homes and 288 kW on churches totaling over 71,000 square
feet.
> Installations were limited to gable roofs in good condition with 1/2 inch
or
> thicker plywood and composition shingles less than 10 years old. Solar
panels
> with 7 Solec SQ80 modules (4.33 ft x 13.5 ft) were fastened to roofs with
24
> each 1.5-inch #10 stainless steel wood screws through 0.25-inch thick
aluminum
> mounting feet and into the plywood. We hired local electricians and
trained them
> how to make water-tight roof attachments. We paid a construction
specialist
> (retired general contractor with over 50 years experience) to fly to
Sacramento,
> review our design and observe installers at work. To date, there have been
no
> roof leaks despite the worse rainy season in 100 years in 1994-95, several
> storms since then, winds over 80 mph at some sites and a few minor
earthquakes.
>
> I used the same screw mounting on my own PV system, but I don't recommend
> fastening PV arrays with screws into plywood or other "out of the box"
designs
> unless you are willing to do your homework, get stamped drawings and calcs
from
> licensed engineers and pay a fair price for experienced supervision and
quality
> work.
>
> Peace,
> Joel Davidson
>
>
> "Jeffery Wolfe, Global Resource Options" wrote:
>
> > Keith,
> >
> > When I don't get things really engineered, I tend to build a battleship.
> > (Maybe an unfortunate analogy tonight.)
> >
> > I'd consider installing a long piece of angle below the roof purlins,
> > spanning several purlins or beams (depending upon design of the roof
> > structure). I'd then put the same type of angle above the roof, and
clamp
> > the two together with bolts. Doesn't need to be real heavy angle, the
object
> > is simply to create a solid sandwich.
> >
> > Short of that, I've also taken 5/16" all thread rod and bent it into a
"U".
> > Both ends stick through the roof and hold a foot in place, with the U
going
> > around a rafter. (I was on a wood roof.) This particular construction
> > survived some pretty good midwestern thunderstorms, but was not
subjected to
> > any hurricanes.
> >
> > I still haven't got the courage, or the engineering back up, to simply
use
> > surface screws for any panel installs. Joel had some stuff he sent
around a
> > while ago on some screw attached racks he had engineered for SMUD (I
think).
> > But then you're trusting that for 20 or more years the plywood doesn't
> > degrade, and the screw material doesn't corrode, and that's not a great
bet
> > with small diameter fasteners. Bad enough with lags into 2x's!
> >
> > My 2 cents.
> >
> > Jeff Wolfe
> > Global Resource Options
> > Selling Solar and Working for Peace
>
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