Uplift Wind Loading Values [RE-wrenches]

keith kcronin at lava.net
Wed Mar 19 22:12:42 PST 2003


Hey Matt

Have you or any of the wrench ensembles ever installed or touched one of
the new SAPC zero penetration systems that they have touted?

I thought a wild dream to this flat roof dilemma would be to get some of
that liquid roofing stuff that the roofers use. Create a "frame" for it
for the size array you desire on a particular roof.  Embed your solar
strut or equivalent before she dries, and encapsulate it with some uv
protectant the roofers use.  This way it does 2 things. First, zero
penetrations. Second, another roof with more R value.

Or, put down the foam 4x8 sheets like roofers & Powerlight, and use the
20 year rubber membrane encapsulating material.

I still prefer mechanical hardware. I am like Matt.  The perpetual
squeezing and shaking down of customers hasn't fully gained a firm
footing here yet.  I could only imagine the potential for a piranha pool
in California.  Ultimately, these things need to last more than the
warranty period!  Its cost over time! Not the installed price!

Aloha

Keith Cronin
Island Energy Solutions
318 A Kuulei Road
Kailua, Hawaii 96734
808-262-3268 Tel
808-263-0338 Fax
www.islandenergy.net



-----Original Message-----
From: Matt Lafferty [mailto:pvpro at attbi.com] 
Sent: Wednesday, March 19, 2003 7:39 PM
To: RE-wrenches at topica.com
Subject: RE: RE: Uplift Wind Loading Values [RE-wrenches]

Keith asked:

is it possible to use self tapping screws into a corrugated roof that is
supported by z bar purling for pv racking support?  Or is it advisable
to drill the 90 degree angle iron that makes the z bar purling assembly
and have threaded rod through the roof? I feel this might be better to
limit the compression on the corrugation and the roof.  What is the wind
rating or perhaps a mechanical engineer would know how many self tappers
x width of screw or just go for threaded rod and sleep better!

All:

It seems to be the "method du jour" of late in California to use Tek
screws to fasten a PV Rack atop a corrugated metal roof with Z-purlins
as the sub-structure.  One installation currently underway that I know
of is literally on the beach and, therefore subject to the highest
Category of Wind Design.  (I'm not involved in the project, for the
record).

The attachment is made directly through the roof material and into the
Z-purlin.

I have looked at the "engineering" for the uplift calculations and am
left scratching my head.....Why is it this engineer uses such a low #/sf
uplift (approx 7 psf) when all the requirements I've read say 25 psf for
this Wind Category?  What will happen in a year or three?  Using a
single #12 Tek per 10 s.f. of glass to hold this all together?  Are you
sure you have E&O insurance, Mr. Engineer?

This is not the only example (quite a few as a matter of fact) of
shoddy/irresponsible engineering that I've seen applied to Roof
Attachment.  I digress from expounding on those at this time, but
suffice it to say, Installer Beware if you are relying on this kind of
crap!

I have further issues with this method....Keith is right.  Compression,
and the resulting tearing of the sheet metal around the screw is a leak
waiting to happen.  It's one thing if it's a barn (that doesn't make
leaks right, just less costly to repair) but it's an entirely different
issue if it's a finished ceiling below.

What about the black-eye that results when a publicly accessible and
viewable system "leaves the roof"?  The quality of labor and lack of
quality control I've seen installing in this manner has not demonstrated
to me, at least, a level of care that I would have representing me,
especially if I were relying on "low-ball" engineering to provide my 5
year warranty.  "Spinners", snapped screw heads (read this as ZERO
attachment), non-perpendicular screw alignment, etc.  My term for all of
these is "Air Screws".

I am with Keith.  Bolt the darned thing down.  Seal it well.  Sleep
tight!

-Matt Lafferty
mlafferty at universalenergies.com

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://www.topica.com/lists/RE-wrenches/

List rules & etiquette: http://www.mrsharkey.com/wrenches/etiquete.htm

Check out participant bios: www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://www.topica.com/lists/RE-wrenches/

List rules & etiquette: http://www.mrsharkey.com/wrenches/etiquete.htm

Check out participant bios: www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com

==^================================================================
This email was sent to: michael_welch at sbcglobal.net

EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9.bWljaGFl
Or send an email to: RE-wrenches-unsubscribe at topica.com

TOPICA - Start your own email discussion group. FREE!
http://www.topica.com/partner/tag02/create/index2.html
==^================================================================





More information about the RE-wrenches mailing list