6 or 4 foot on center roof mounts

[John.DS99]

I saw another thread that mentioned this, but the answer was "what do you mean."

Well, don't try that here, because that is my question. What does it mean in reference to mounting solar panels.

Here is my local code
Begin
This is to clarify the non-engineered requirements for solar photovoltaic (PV) and solar water heating systems, hereby referred to as solar energy systems for 1 & 2 story single family and duplex.
1. (deleted for brevity)
2.The solar energy device top of panel is installed within 12” of the roof plane below.
6.Modules do not overhang any roof edges (ridges, hips, gable ends, eaves).
8.The plane of the panels is parallel to the roof.
9.There is a 2” minimum and 10” maximum between the underside of the module and the roof surface.

NOTE: Panels shall be adequately anchored to the roof framing at a maximum of 4’ on center vertically and horizontally.
End - There is more but this should be plenty

I'm asking you what that means,

I know there is some hardware such as a rail that is to be attached to the roof.

How about this (for a guy whose house has rafters in one direction only that are exactly 4 feet apart as mine are).
A. You can put the rails anywhere the hell you want as long as you only secure the rail with a screw/bolt into a rafter.
B. The panels need to be exactly 4 feet apart (say, center to center).
C. You can't because the solar panels are 4 by 6 feet and they have to overlap which is ridiculous (4 feet on center horizontally & vertically).
D. You must place the rails at exactly 4 feet apart so if your panels were 3 feet wide, they would have to touch only one rail (assuming the rails are vertical only).
E. The rails must be mounted vertically or horizontally at 4' intervals but the bolts don't have to be secured into the rafters.
Other explanations - are any of these true or do they all miss the point?

Thanks

 

[jjww]

A. yes
B. panels abut along the rails
C.panels that are 4 x 6 FEET?? holey cow- still abut them on the rails- the rails have to be fastened to the rafters,every 4 (or 6 ft in my case)not the panels
D.Why place the rails at 4 ft? rail spacing is dictated by the panel requirements.
E. rails have to be secured against wind loading- pretty much always means attached to rafter
i just read the Sunnyvale requirements and yes it does say the PANELS have to be fastened every 4 ft but i bet that means the rails if you have rails.
most rail systems are pre engineered for wind loading which is why mine are mounted to rafters every 6 ft(Iron ridge-just a satisfied customer -they were available locally with free shipping)

 

[darrell2002]

Maybe you are confusing rail mounting with panel mounting. Only the rail mounting hardware needs to be spaced at 4', not the panels. Panel spacing is whatever will fit on the rails with the panel mounting hardware. Rail to rail spacing is dictated by the panel height or width if the panels are portrait vs landscape. Make a project at Ironridge & all will be cleared up. Here is mine with 2' trusses staggered at 4' according to California Solar Permitting Guidebook. 4' rafters are not shown in the guidebook. You may need to get a structural evaluation done

 

[Mike 134]

Post #3 is your correct answer.

 

[John.DS99]

Thanks all for the help.

I have three brands of panels, but mainly I will be using Trina Vertex S which are 1754 x 1096 mm, or 69" x 43" 390 watt panels.

Code says Panels shall be adequately anchored to the roof framing at a maximum of 4’ on center vertically and horizontally.

Rails are the Anchors
Rafters are my Roof Framing
4 feet on center horizontally needs no further thought in my case
4 feet on center vertically - What does this mean? anything? Maybe it doesn't matter in my case.

How about we argue the orientation of the rails? If the rails had only 1 bolt to anchor, they could be oriented as I wish.
Mine clearly have multiple bolt holes so they can only be aligned along the rafters.


I know where my rafters are.


They are exactly 4' apart.

 

[Mike 134]

Thanks all for the help.

I have three brands of panels, but mainly I will be using Trina Vertex S which are 1754 x 1096 mm, or 69" x 43" 390 watt panels.

Code says Panels shall be adequately anchored to the roof framing at a maximum of 4’ on center vertically and horizontally.

Rails are the Anchors
Rafters are my Roof Framing
4 feet on center horizontally needs no further thought in my case
4 feet on center vertically - What does this mean? anything? Maybe it doesn't matter in my case.

How about we argue the orientation of the rails? If the rails had only 1 bolt to anchor, they could be oriented as I wish.
Mine clearly have multiple bolt holes so they can only be aligned along the rafters.


I know where my rafters are.

View attachment 192945View attachment 192946
They are exactly 4' apart.

How thick is the rigid insulation on top of the roof boards?

 

[jjww]

have you reviewed the TRINA installation guide? Dont have to use the mounting holes in the panels...

https://static.trinasolar.com/sites/default/files/PS-M-0434%20A%20Installation%20Manual%20of%20Standard%20Module_IEC_UL_2016_A.pdf

 

[zanydroid]

There is enough permitted grid tie solar in Sunnyvale that you can walk around and look at how people have done it, to get some potential solutions to this. And you can focus too on houses with same 4 ft exposed rafter spacing as you.

You can ask on local forum (EG Nextdoor) for copies of approved plans from neighbors. I have supplied it when asked.

You will need the rails positioned in a compatible location to the attachment range on those panels.

The 4 ft rule, whatever that means, is most likely less constrained than what the manufacturer/engineer needs you to do.

In my town on the peninsula, 4 foot rafter spacing would require engineering stamps, in which case it is not super critical to understand this directly yourself, as you anyway need to outsource the plans set. Plus the manufacturer engineering tables may not go up to 4 ft.

You will get another chance at checking understanding via review comments after submitting it.

Where understanding the rules and engineering guidelines becomes important is if you find that the conditions differ from what was in the diagram, and you need to make field adjustments. With such a wide spacing you probably want to triple check the plans.

 

[MTM98290]

I used Ironridge rails that I purchased locally through Platt.com, no shipping. They work well and are easy to install. I'm sure there are others as well.

Xr10 -6 foot span
Xr100 -8 foot span
Xr1000 -12 foot span

I'm not sure if these specs can be used for to the fact that they have engineering approval for these specs, or if the more stringent 4' is required, but it something to look into. XR100 or XR1000 would be more than adequate for the 8' span if that is allowed, although I am doubtful that it is given what you posted.