Need advice on drawings

[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.

[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.]

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]

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

What is it then?

[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 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.

[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

[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.

[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.

[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?

[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]

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.

[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.

[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

[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.