Need advice on drawings

[inetdog]

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

Is this an open 20' span from wall top plate to ridge? Or are there additional bracing members that change the rafter to part of a truss?
The latter changes the calculations considerably.

Have you figured out how many layers of shingles are on the roof currently? Or is it new enough that there is just one layer?

If I were the inspector I would not be satisfied with just the calculations of load in pounds per square foot that you mentioned. I would also look at (or ask for evidence that a PE has looked at) the specific point loads and in particular the ability of the attachment points to withstand the worst case wind uplift of the array. The IronRidge calculator includes those calculations too.

[J.P.M.]

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...

G.T.C: Meant in a professional way - If you are intending a safe design and a reasonably competent analysis, there is a lot more to it than calc'ing a bending stress. You appear way out of your depth. If your analysis gets you through/by the building/plan inspector, I suspect it won't be because it's done using generally accepted methods. In the end, it's all about safety.

No offense intended, but it seems to me you have no idea what's required at this stage, or more importantly why. Calculating imposed loads on structures, and how the structure deals with and responds to those loads is not something to be done as an afterthought, or treated as casually as you seem to be doing. It is serious business. People can be hurt or worse.

Take what you want of the above. Scrap the rest.

[samotlietuvis]

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...

GreenTeeCrazy, see attached "California Structural Solar Toolkit Document 5" Table 2. For you 2x6" rafters at 16", pre 1960 home can have 17' Horizontal Span, and post 1960 home can have 14'4" Horizontal Span. Your 20' span is just too long, and that's for California where snow loads don't play big part in most of the areas. You can read the document to see what assumptions were made in creating the table.

If I were you I would brace the 2x6" that will have solar attachment points installed at 10' span. So if your attachments at every 2nd rafter then a brace every 32", and 3rd rafter then a brace every 48". Remember that you need a safety factor on your calculations to feel good (I like at least 2X).

I am not structural engineer, but I will throw in my $.02. One thing is to show that your beam deflect a certain amount for a 2x6" at 20' length at your distributed roof load and you are this much from failure (note solar attachment points are not distributed load). That's considering one 2x6” beam cross section only and you are not considering your 2x6" beam joints and what they can handle and how they respond to the excessive bending. Performing joint calculations is much harder.

If you over-brace it, then you may not need structural engineer (SE) calculations and wet stamp, and you will feel good yourself that your solar is on the strongest part you’re your roof. If you only knew how hard it is to become an SE… I know a few guys who are aspiring to become SE’s and I don’t envy them. If I had to guess, SE time and stamp are not cheap…

ToolKit Document 5 Table 2.jpg

[GreenTeeCrazy]

No offense is taken, All is good here. I started the thread to educate myself and for anyone looking at DIY.

Absolutely I thought all i had to do is show some numbers and some drawing and i should be good to go, but this is turning into a mercury poisoning, slow mental tormenting.

This was just the building inspector, I am still waiting for the Elec. inspector to call me... shaking my head.

By the end of the week i'll be making phone calls around my area for some estimate for civil and electrical Engineering with a PE wet seal.

Yes, the 20' is one solid piece, from ridge to wall (overhang). I did install few 2x4" blocking at about 10" on every rafter supporting the quickmount penetration. and the roof has only 1 layer which was done last year. so i dont have to worry about more weight.
And correct in assuming max allowed is for the breaking point of the rafter.

[inetdog]

And correct in assuming max allowed is for the breaking point of the rafter.

No, and if you even suspect that, you are indeed over your head.

[GreenTeeCrazy]

No, and if you even suspect that, you are indeed over your head.

What is it then?

[J.P.M.]

What is it then?

It's a lot of other things you appear to be completely unaware of. DUDE: IT'S COMPLICATED IN WAYS YOU APPEAR TO EVEN IMAGINE ! THIS IS SERIOUS BUSINESS. PERSONAL INJURY OR WORSE CAN BE THE RESULT WHEN OF ATTITUDES AND IGNORANCE SUCH AS YOU EXHIBIT ARE ALLOWED TO PREVAIL.

It appears you are attempting to put the cart before the horse in terms of engineering knowledge, and are unaware of the fundamentals necessary before more sophisticated and necessary tasks are tackled.

People spend a lot of time and effort getting education and experience to be able to do what you seem to casually dismiss as something only necessary to satisfy some bureaucrat. When they make mistakes, they pay, either in reputation, money, conscience or more. When there is malfeasance, they may go to jail.

Codes exist for a reason besides giving people crap. It's called safety.

[GreenTeeCrazy]

It's a lot of other things you appear to be completely unaware of. DUDE: IT'S COMPLICATED IN WAYS YOU APPEAR TO EVEN IMAGINE ! THIS IS SERIOUS BUSINESS. PERSONAL INJURY OR WORSE CAN BE THE RESULT WHEN OF ATTITUDES AND IGNORANCE SUCH AS YOU EXHIBIT ARE ALLOWED TO PREVAIL.

It appears you are attempting to put the cart before the horse in terms of engineering knowledge, and are unaware of the fundamentals necessary before more sophisticated and necessary tasks are tackled.

People spend a lot of time and effort getting education and experience to be able to do what you seem to casually dismiss as something only necessary to satisfy some bureaucrat. When they make mistakes, they pay, either in reputation, money, conscience or more. When there is malfeasance, they may go to jail.

Codes exist for a reason besides giving people crap. It's called safety.

Having a bad day?
No need for shouting dude! I'll take criticism and advices but please no need for name calling,
I am here on this forum asking questions cause I am not familiar with this kind of profession, not because I am not educated but because this not my line of work. The simplest thing maybe was to try and give an answer, just because you know more that doesn't give you the right to call anyone an idiot.
I think coming here on this forum and asking stupid questions was a bad idea.
Maybe you should of spent more time reading my previous post that I already said that by the end of the week I'll be looking for a PE to get the work done, but you are so smart that you missed that part.

Time to move on.

[J.P.M.]

Having a bad day?
No need for shouting dude! I'll take criticism and advices but please no need for name calling,
I am here on this forum asking questions cause I am not familiar with this kind of profession, not because I am not educated but because this not my line of work. The simplest thing maybe was to try and give an answer, just because you know more that doesn't give you the right to call anyone an idiot.
I think coming here on this forum and asking stupid questions was a bad idea.
Maybe you should of spent more time reading my previous post that I already said that by the end of the week I'll be looking for a PE to get the work done, but you are so smart that you missed that part.

Time to move on.

Not a bad day at all.

1.) If you spent more time reading my posts to this thread, you might notice the word idiot does not appear in any of them.

2.) Nor do I engage in other name calling, directed at you or anyone else.

3.) Disagree all you want, I appreciate lively discussions, but if you do disagree, I'd suggest you get it straight. Please do not accuse me of things I did not do and/or did not write.