Uplift Wind Loading Values [RE-wrenches]

[Joel Davidson]

Bill,
I quit Solec September 1996 and never did work at PVUSA. What's your point?
Joel Davidson

Bill Brooks wrote:

> Joel,
>
> I'm talking about the exact Solec system that was installed on over a
> hundred homes in Sacramento. Identical mounting technique, identical
> hardware, same Ananda junction box, identical everything. This was not a
> SMUD design--it was the design that came as a result of the second Pioneer 1
> solicitation--this is, in fact, the design you were referring to.
>
> Bill.
>
> -----Original Message-----
> From: Joel Davidson [mailto:joeldavidson at earthlink.net]
> Sent: Monday, March 24, 2003 6:51 PM
> To: RE-wrenches at topica.com
> Subject: Re: Uplift Wind Loading Values [RE-wrenches]
>
> Hi Bill,
> I had nothing to do with any systems at PVUSA. SMUD probably decided to use
> the
> screws-into-plywood method because they liked it. Now that UniRac offers
> slotted
> rails so you can hit the rafters with sliding feet, lag bolts are a lot
> easier
> and stronger when they hit a nice solid rafter on center.
> Best regards,
> Joel Davidson
>
> Bill Brooks wrote:
>
> > Joel,
> >
> > You did not personally do the system at PVUSA, but the same folks who
> > installed the SMUD systems did the one at PVUSA for SMUD. It was part of
> > SMUD's small system's testing. This was real 1/2" plywood, not OSB.
> >
> > I've looked at every residential roof mounting technique to date, and 3.5"
> x
> > 5/16" stainless lags in roof structure beats them all hands down.
> >
> > Bill.
> >
> > -----Original Message-----
> > From: Joel Davidson [mailto:joeldavidson at earthlink.net]
> > Sent: Sunday, March 23, 2003 7:58 AM
> > To: RE-wrenches at topica.com
> > Subject: Re: Uplift Wind Loading Values [RE-wrenches]
> >
> > Dear Bill,
> >
> > I did no systems at PVUSA.
> >
> > Tom Lane is right about the pre-chewed substitutes used in place of
> plywood.
> > OSB
> > can be used in glue-ups but has poor fastener properties. Second and third
> > growth framing lumber is also pretty wimpy. In the 1960s, I started using
> > hotdip
> > galvanized nails to frame up buildings after reading a study about box and
> > common nails  losing 50% of their holding power in green framing lumber in
> > the
> > first year. Some builders use glue and screws like cabinet makers to build
> > solid
> > homes, but most residential and commercial buildings are not as well built
> > as
> > the PV arrays on them.
> >
> > Best regards,
> > Joel Davidson
> >
> > Bill Brooks wrote:
> >
> > > Joel,
> > >
> > > The only one of those system's I'm intimately aware of was mounted at
> > PVUSA
> > > on 1/2" plywood. Over half the screws had lifted 1/4" to 1/2" out of the
> > > deck providing for a nice path for water into the roof over time. They
> > were
> > > all gooped with a copious amount of sealant, but the problem was the
> > > fasteners were unscrewing because there was insufficient friction force
> on
> > > the plywood.
> > >
> > > This was not a pullout issue. I believe that 1/2" plywood is strong
> enough
> > > for the application even though, as Tom points out, it is almost never
> > used
> > > anymore--only OSB for the last decade. The problem is that the screws
> > > unscrewed, either through thermal cycling or wind vibration. Many
> > > jurisdications in California will not accept any fastener method without
> a
> > > minimum of 1" into the wood. I'm not trying to rag on the system too
> bad,
> > > but I would never recommend that method. If they haven't leaked yet, get
> > > ready---it will happen.
> > >
> > > That experience, along with similar problems with other
> > wood-screws-in-deck
> > > schemes have brought me to the conclusion that lags into rafters or
> > trusses
> > > is the ONLY viable roof mounting technique. There are several good
> designs
> > > out now that allow for proper installation---use them. I don't mean to
> > rain
> > > on your parade, but.....
> > >
> > > Bill.
> > >
> > > -----Original Message-----
> > > From: Joel Davidson [mailto:joeldavidson at earthlink.net]
> > > Sent: Saturday, March 22, 2003 4:17 PM
> > > To: RE-wrenches at topica.com
> > > 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

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