Need advice on drawings

[inetdog]

And, for the casual readers, note that we are talking about the grounding wires (EGC, green or bare) not the grounded neutrals (white or gray). The neutrals from different branch circuits must never be connected except at the source panel of the branch circuits.

[GreenTeeCrazy]

Hello again.
I am not holding no one responsible in this forum, all i say is thanks for the support.

The inspector is requiring me to show them that the roof can hold the weight of:

-dead load
-snow load
-solar system weight
etc...

My roof is:
16" rafter spacing
2" x 6" x 20'
23 degree angle

Any idea on how to put all the numbers together to come up with a number that shows the roof can support atleast 70 psf?

[J.P.M.]

Hello again.
I am not holding no one responsible in this forum, all i say is thanks for the support.

The inspector is requiring me to show them that the roof can hold the weight of:

-dead load
-snow load
-solar system weight
etc...

My roof is:
16" rafter spacing
2" x 6" x 20'
23 degree angle

Any idea on how to put all the numbers together to come up with a number that shows the roof can support atleast 70 psf?

Since you ask:

1.) Get the structural plans/drawings/calcs for the building/structure.

2.) Get a copy of ASCE 7 and calc all the required loads.

3.) Check the structure to see if it will withstand the imposed loads calc'd in 2 above.

Or,

4.) Find a structural or other engineer w/ a P.E. license/stamp who's professionally knowledgeable in structural and ASCE 7, and have 1, 2 & 3 above done by that individual. There is probably more to it than you may think.

[Sunking]

Any idea on how to put all the numbers together to come up with a number that shows the roof can support atleast 70 psf?

The answer cost $500, I throw in my PE Stamp for free.

[tehan]

Hello again.

The inspector is requiring me to show them that the roof can hold the weight of:

-dead load
-snow load
-solar system weight
etc...

Any idea on how to put all the numbers together to come up with a number that shows the roof can support atleast 70 psf?

The online design tool on the IronRidge website will do all of these calculations for you. I would at least try that and see if the inspector will accept it. If not, go to a PE because it's unlikely the inspector will accept anything your do yourself.

[GreenTeeCrazy]

WOW! you guys give up so easy

The Questions that i asked are half the answer, I am sure i'll be able to find a solution even if i have to read a beginner's book to Architectural engineering.

I need to do more research and come up with a solution, I have a long holiday weekend and i am sure the answer is out there.

$500... is that how much it cost? I had no idea, I thought the whole complete permit paperwork will cost that much

[J.P.M.]

WOW! you guys give up so easy

The Questions that i asked are half the answer, I am sure i'll be able to find a solution even if i have to read a beginner's book to Architectural engineering.

I need to do more research and come up with a solution, I have a long holiday weekend and i am sure the answer is out there.

$500... is that how much it cost? I had no idea, I thought the whole complete permit paperwork will cost that much

I kind of suspect it will take more than you envision, but good luck. I'd not take the task as lightly or cavalierly as you seem to be treating it.

[Sunking]

$500... is that how much it cost? I had no idea, I thought the whole complete permit paperwork will cost that much

Permitting is a whole other issue. Depending on where you live, permit cost are based on Project Dollars, a percentage, plus Inspection Fees. Getting your drawings and plans is none of the Jurisdiction problem, you own that problem and all expenses that come with it. Us engineers are like doctors and lawyers, we did not spend 8 to 16 years in college to work for free.

Yep it would cost you $500 for me to review and stamp your plans, that is if I approve. If not you get to do them again at added cost. After 4 or 5 tries you realize you just should have paid me $1000 to do the plans and submit to the Planning Office. I would bill you every time you walked in my office just like a Doctor or Lawyer.

I don't know what city you live in, but some jurisdictions will only accept Stamped Drawings and Plans by a PE. If that is the case in your jurisdiction, you can draw and calculate until you grow old and they will not accept anything from you. Makes things real easy on a City, County, or Jurisdiction. Relieves them of responsibility and having to keep people on the payroll to examine building plans. You bring in your Stamped Drawings and the clerk with a High School education making minimum wage issues you a permit. If anything goes wrong and there is a law suite, whoever you contracted to do the design gets held responsible, the City gets off free.

[sdold]

I think what's happening is that even though you can show calculations for the uplift forces, fastener strength, down forces (weight, wind), there is still the unanswered question of whether or not the roof structure can support the loads. Some cities don't require engineering if the weight is less than some figure, like 5 psf. Other cities apparently require engineering for anything. My city was sort of in between, they told me I needed an engineer to look at it, but when I told them the dead load of the panels made live loads (like workers) impossible, that satisfied them. Or else they were tired of me and just wanted me to leave.

I think if you can use a tool like Ironridge or ASCE 7-10 to figure the loads caused by the panels, it would be worth a few hundred dollars to pay an engineer to look at the structure and sign it off if it makes the rest of the job go smoothly. In CA, I believe the permit fees are limited to administrative costs only. Regarding permit fees: My fees were originally around $600, and when I sent them this link http://www.solarpermitfees.org/SolarPermitLawsSumCA.pdf, the fee dropped to about $300.

[foo1bar]

WOW! you guys give up so easy

The Questions that i asked are half the answer

The questions you ask are not half the answer - they are just the question that need to be answered.

Calculating capacity of a roof is not something that knowledgable people will take lightly.

Here's a thread on another board with much the same responses (ie. "get a qualified person to do it")

http://www.eng-tips.com/viewthread.cfm?qid=108324

As for whether your roof should be able to support the weight - I assume you have 1 layer of shingles and not 2?

Are two layers allowed by your AHJ? (They likely are - I think most places allow 2 layers)

Would a second layer of shingles be more or less weight (psf) on your roof than the panels?

Since it'd more more weight, it seems logical that the weight of the panels won't be a problem.

BUT even though you have a logical reasoning that "it shouldn't be a problem" - that doesn't give you an engineering documentation that you're OK. (And it sounds like the AHJ is asking for the engineering documentation.) I haven't ever done those calculations. You may or may not be able to do the research to do them and do them correctly - but I'd expect it to take you a while to do. So my choice would be to do some preliminary calcs (maybe 2 hours of research and calculating) - then contact the AHJ with the logical reasoning that there won't ever be a 2nd layer of shingles - NOR anybody walking in that area. Plus the rudimentary (and likely incorrect) calcs that I had done.
Possibly they'll take that - possibly not.
If not, then you get a PE to do the work, because that's going to save you time. At least at that point you'll have all the dimensions ready for him, including rafter/truss diagrams & measurement. Identity of what kind of lumber was used, etc.

[GreenTeeCrazy]

@Sunking I will not disrespect you or anyone for all the years that they spent on their educations, as you said no one works for free. including me.

Over here in NJ, i have to show them that:
dead load + live load (snow load) + solar panels including the the mounting hardware (858 lbs. divided by roof sq footage) is less than what the roof can support
Roof Weight= 10 psf + 30 psf + 2.6 psf = 42.6 psf is lower than max roof weight limits.
I was told as long as i can provide solid number to support my calculations they will not have no problem with my Construction Permit Application.

I'll try one more time next week with the town inspectors, if not approved by then i'll start looking at civil engineering office for their support.

@sdold, lol... i've been to their office over 4-5 time already not including phone calls. maybe they will sorry for me

@ foo1bar, my roof was done last year, 1 layer. by permit.

"an engineering documentation that you're OK" <== big hump to jump over

[Naptown]

2x6 16"OC at a 20' span is enough to make me run away.
You will have point loads all over the rafters.
Have fun calculating all of them.
Save a lot of grief and hire a structural engineer. I do all the time. Something goes wrong it's their problem.

[foo1bar]

solar panels including the the mounting hardware (858 lbs. divided by roof sq footage)

I'd divide it only by the amount of roof area covered by solar panels.
Your statement could be interpreted that you are dividing by entire roof area.

And I'd probably add a little fudge factor for extra items you might not have included already like wire, conduit, wire clips, roof sealant, etc. - so 858 might instead be 900 lbs.
(Of course I didn't come up with 858lbs - so I have no idea if that's the right number)
I'd still expect it to be fairly small psf number.

[GreenTeeCrazy]

numbers, numbers and more numbers...

I cant do much anyway til Tuesday due to the Holiday. but i'll revise my proposal one more time and if it doesn't go through then i'll be contacting a PE.

858 lbs. is the number from ironrodge website for a 18 panels with mounting hardware and inverters.
330 is the total sq ft of PV area
858/330=2.6 as long as this number is lower than 5 lbs/sf then i'm in good shape.

2x6" @ 20' w/16" OC isnt that bad compare to 24"OC.

I did crunch some numbers on 2x6" rafter and it takes a lot of psi for bending stress on roof to surpass the Max allowed for Hem-Fir (assuming that is what was used for the north east back in the 50's and 60's).

back to researching...

[foo1bar]

I did crunch some numbers on 2x6" rafter and it takes a lot of psi for bending stress on roof to surpass the Max allowed for Hem-Fir (assuming that is what was used for the north east back in the 50's and 60's).

back to researching...

"max allowed" - is that max allowed for a specific given deflection?
Or max before it potentially breaks?