Structural calculations PE wet stamp required ???

[samotlietuvis]

Guys,

Second time around I am performing solar install on my personal new home I just bought. I moved south 10 miles from Lancaster, CA to Palmdale, CA, both hot desert towns. Went through learning curve on my first home in Lancaster, CA and I was under assumption that permit drawing in Palmdale, CA will be a breeze.

Oh boy I was wrong. I am going to pick up my approved permit today, but what I get is a marked up sheet with corrections. Felt like I was getting a graded college homework from an inspector (not an engineer), and after inquiring I found out there is not a single PE is the department where I was submitting my solar permit. Main points that struck me are:
- Palmdale, CA does not approve expedited PV permitting process signed by Governor’s Office of Planning and Research in 2014. Town 10 miles north (Lancaster) is more than happy to approve expedited PV permitting
- Palmdale CA snow load is 20psf. That’s a good one. Ten years living in the area I have seen snow ~ 6” once and it lasted ~12 hours. It is a hot desert town. Not sure where that number comes from. I hope I am not asked to design for some very unlikely snow event.
- I must get structural calculations performed and wet-stamped by licensed engineer; That’s a good one. How about I perform my calculations per code, and department PE approves it?

In my permit I did show that
1. Weight/Attachment = 23.4 lb
2. Distributed Weight of PV Module = 3.0 lb/sqft
3. Factor of safety of 4x per attachment point based on max wind pressure.
4. That my racking system (IronRidge) and roof attachment system (Quick-Mount PV S-hook) have CA PE structural engineering approval.

I am a mechanical engineer myself - not licensed because no need, but passed FE after school, and I do plan getting my PE license at some point.

I asked the permit guy to show me the code where wet-stamped structural calculations are required. He will get back to me on that one. Not making any friends in the permit office…

Did more reading on Governor Brown expedited permit process bill and:
“Assembly Bill 2188 (Muratsuchi, 2014) requires local governments to adopt an administrative ordinance that creates a streamlined permitting process for small rooftop solar system installations on or before September 30, 2015.”

Hopefully places like Palmdale CA will be forced to adopt expedited permit process and will not have their special conditions to draw the permit. It is hard to understand how a department with no PE chooses to impose their own rules to make solar installations harder.

How common are places like Palmdale, CA?
How hard (and expensive) is it finding a licensed engineer to wet stamp my structural calculations? I have my attachment point and solar layout and my roof rafters spacing. What’s a good place to look?

[J.P.M.]

I'd do a couple of things: First and perhaps easiest, wait until 10/01/2015 and see if an expedited process is in place, and second, do the struc. calcs yourself and if you have a qualified P.E. where you work or if you belong to any eng. organizations (A.S.M.E. ?), ask around and see if one of those folks who may be qualified will review and sign off/stamp the calcs.

[samotlietuvis]

I'd do a couple of things: First and perhaps easiest, wait until 10/01/2015 and see if an expedited process is in place, and second, do the struc. calcs yourself and if you have a qualified P.E. where you work or if you belong to any eng. organizations (A.S.M.E. ?), ask around and see if one of those folks who may be qualified will review and sign off/stamp the calcs.

I was ASME member ~10 years ago when I was finishing school, but I haven't been renewing. I will do another permit attempt with full ASCE 7-05 wind calculations showed, and then if no luck, wait for a month to see if they adopt Expedited Permitting Process.

So sad to see that the next town North (Lancaster, CA) is one of the most solar friendly towns in USA and the first town is USA to mandate 1kw solar system for new construction. Even solar fees are 6X cheaper in Lancaster than Palmdale that has their own permit rules and 20psf (~16") of snow load in the desert.

Any idea how I combine 20psf snow load with ASCE 7-05 wind calculations? Do I just add 20psf snow load to design wind downward pressure, or there is more to it?

[inetdog]

Any idea how I combine 20psf snow load with ASCE 7-05 wind calculations? Do I just add 20psf snow load to design wind downward pressure, or there is more to it?

Pretty much that, but then do a separate calculation for the wind uplift, which puts different stresses on racking and connection points.

[J.P.M.]

I was ASME member ~10 years ago when I was finishing school, but I haven't been renewing. I will do another permit attempt with full ASCE 7-05 wind calculations showed, and then if no luck, wait for a month to see if they adopt Expedited Permitting Process. So sad to see that the next town North (Lancaster, CA) is one of the most solar friendly towns in USA and the first town is USA to mandate 1kw solar system for new construction. Even solar fees are 6X cheaper in Lancaster than Palmdale that has their own permit rules and 20psf (~16") of snow load in the desert. Any idea how I combine 20psf snow load with ASCE 7-05 wind calculations? Do I just add 20psf snow load to design wind downward pressure, or there is more to it?

Don't forget to check what the solar structure is attached to for possible loadings not considered when the structure (assuming a roof mount) was built.

[samotlietuvis]

Don't forget to check what the solar structure is attached to for possible loadings not considered when the structure (assuming a roof mount) was built.

J.P.M, if I show in my drawing that I have 3:12 Pitch roof that uses 2"x4" construction with 24" rafter spacing, Spanish S-Tile Roof, home and roof is 10 years old (post 1960). I will go into attic this weekend and measure my horizontal rafter span. Given all the information and using "Toolkit Document #5" (Structural Criteria For Residential Rooftop Solar Energy Installations) table 2 for tile roof, I will show that my roof meets California building and residential construction. Is that good enough, or do I need to perform some calculations?

[J.P.M.]

J.P.M, if I show in my drawing that I have 3:12 Pitch roof that uses 2"x4" construction with 24" rafter spacing, Spanish S-Tile Roof, home and roof is 10 years old (post 1960). I will go into attic this weekend and measure my horizontal rafter span. Given all the information and using "Toolkit Document #5" (Structural Criteria For Residential Rooftop Solar Energy Installations) table 2 for tile roof, I will show that my roof meets California building and residential construction. Is that good enough, or do I need to perform some calculations?

Hard to say. Depends on the engineer whose stamp is on the line. I was quite familiar with structural design, but I never claimed that as an area of proficiency. I'd usually do what sounds like what you plan - do the meatball engineering design on simple stuff and take my spoor over to the civil engineers for review/revision and eventual stamping and hard core structural deign if/as required. If it was me in your situation, I probably wouldn't go to the lengths of calculating moments of inertia/section moduli, but I'd at least go far enough to feel reasonably sure via calculation and inspection of the site that whatever structural members are taking the imposed loads, static, dynamic and occasional in combinations required by local code, probably ASCE - 5 or -10 are robust enough to take the loadings. Don't forget the fasteners.

[inetdog]

Some manufacturers of racking provide detailed drawings including structural calculations on request. Possibly even stamped by their PE. Whether they would be acceptable to your AHJ then becomes the question.

[Naptown]

Just about every system I do needs wet stamped plans.

[solarix]

Yep, A lot of building departments are adverse to liability and want some one else to be responsible for everything possible (of course, they still want all the power). Find a no-job-too-small PE or even better a friend with any kind of PE license as it doesn't have to be a structural license to satisfy them. Just someone willing to take the liability of a failure.

[samotlietuvis]

Some manufacturers of racking provide detailed drawings including structural calculations on request. Possibly even stamped by their PE. Whether they would be acceptable to your AHJ then becomes the question.

Yes, will provide PE stamped calculations for both Ironridge racking and QuickMountPV roof attachments. Hopefully that will help.

[samotlietuvis]

Yep, A lot of building departments are adverse to liability and want some one else to be responsible for everything possible (of course, they still want all the power). Find a no-job-too-small PE or even better a friend with any kind of PE license as it doesn't have to be a structural license to satisfy them. Just someone willing to take the liability of a failure.

Great point. It felt to me that they want all the power and don't want to take any responsibility themselves. My younger brother designs bridges for living in one of the states and he is becoming a PE this year or early next year, and he works with a lot of PE's and even SE's. Unfortunately, in my line of work nobody has PE certification because it is not necessary. I used to play table tennis with a guy who was licensed SE in Los Angeles - but that was long time ago. No friends with a PE license, but I will work on making some because I plan becoming a PE at some point in my career.

[solarfrank]

Palmdale and LA county are the worst places to get a permit for solar installation. PM for structural engineer.

[samotlietuvis]

Permit approved without a wet-stamp!!!

Now the fun part begins.