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Re: LL on roof with solar panels.

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Gary,
 
        There are three possible load cases you should think about.  These are:
 
1.)    Workers who might be working on the roof plus stacked materials while they're working.  I think the code specifies a minimum of 1.0 kPa (20.7 p.s.f) to account for this.
 
2.)    What happens if you get a big dump of snow overnight?  As a presumption of reasonableness (not a code requirement) I would suggest about 50% of the design snow load as a minimum.
 
3.)    What about snow load while the owners/caretakers are on vacation?  My preference would be to design for the normal snow load.  Better safe than sorry>
 
Regards,
 
H. Daryl Richardson
----- Original Message -----
Sent: Friday, June 15, 2007 11:51 AM
Subject: RE: LL on roof with solar panels.

My question is not whether to treat the panels as live load but rather if there is a need to apply the roof live load in the area where the panels are to be installed.  The panel weight is 3 psf which is typical but the spacing between rail supports is up to 8 feet.  This is what has me concerned with the application of roof live load over the panels which would place a fairly hefty concentrated load on the existing roof trusses.



-----Original Message-----
From: William King
Sent: Fri, June 15, 2007 12:50 pm
To: seaint(--nospam--at)seaint.org
Subject: RE: LL on roof with solar panels.

The definition for Live Load for the I-codes would be the same.  Fixed equipment is a dead load.
 
You would still need to apply the live load to even the area covered by the panels as there may be people on the roof at times maintaining the panels. 
 
-Bill King, PE, MCP


From: Mark E. Deardorff [mailto:mdeardorff(--nospam--at)burkett-wong.com]
Sent: Friday, June 15, 2007 12:39 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: LL on roof with solar panels.

You can't take it as live load, at least not under the 1997 UBC. Table 16-B lists mechanical and electrical equipment with the parenthetical "(dead load)". You still end up with the 0.9 load duration factor though.
 
Mark E. Deardorff, S.E.
Structural Engineer
Burkett & Wong Engineers
3434 4th Ave
San Diego, CA 92103
P 619.299.5550
F 619.299.9934
mdeardorff(--nospam--at)burkett-wong.com
 


From: Bill Cain [mailto:bcainse(--nospam--at)aol.com]
Sent: Friday, June 15, 2007 9:27 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: LL on roof with solar panels.

Gary-
Assuming your roof is wood frame, if you treat solar panels as the Live Load, you should increase the Solar panel load by a duration factor of 1/0.9 to account for the fact the load is likely longer duration than the 10 years assumed for LL per Nds. Most, including mine, are warranted for about 25 years. 

It is not likely to be a problem with the usual weight of the panels in the 3-4 psf range. Normal Code Live load (without solar load) should also be checked without the solar panel load (with a duration factor for wood construction of 1.25) to allow for installation loads similar to the way roofing loads are treated. 
 
Regards,
Bill Cain SE
Berkeley CA

-----Original Message-----
From: garyg(--nospam--at)structuralstuff.com
To: seaint(--nospam--at)seaint.org
Sent: Fri, 15 Jun 2007 8:34 am
Subject: LL on roof with solar panels.

When you have flat panel solar panels on a roof, is there still a need to apply the roof live load to the supporting members?  I've always been taught that yes it would still be required but common sense says that since the solar panels are glass, it is unlikely that there will be any live load while the panels are in place.
 
All opinions are welcome.
 
Gary Grinstead, SE
 
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