Roof Top Rail System - distance between rails?

[BlueMarblePA]

What is the best distance between the roof rack rails?

In this video, he says you have to measure a distance between the holes in the solar panel, and use that distance in order to space apart the rails on the roof. I am confused by this, because the way that the solar panels are clamped on to the rails does not seem to require you to utilize the holes? It simply clamps on to the edge itself.

I would imagine it doesn't really matter. For example, i am using LG panels which are 64 inch tall, and my roof shed is about 60 inch. I was just going to put the rails 12 inch from the bottom and 12 inch from the top of the shed roof which would result in a rough distance of 36 inch between the two rails.



Minute 1:20 of the video

 

[Samsonite801]

What is the best distance between the roof rack rails?

In this video, he says you have to measure a distance between the holes in the solar panel, and use that distance in order to space apart the rails on the roof. I am confused by this, because the way that the solar panels are clamped on to the rails does not seem to require you to utilize the holes? It simply clamps on to the edge itself.

I would imagine it doesn't really matter. For example, i am using LG panels which are 64 inch tall, and my roof shed is about 60 inch. I was just going to put the rails 12 inch from the bottom and 12 inch from the top of the shed roof which would result in a rough distance of 36 inch between the two rails.

You are correct in that you won't be utilizing those factory holes on the bottom flange of the panels, but it is to be assumed or interpreted that the engineers who designed those panels designated the location of those factory holes at a fairly optimal distance apart to adequately keep any potential panel flapping or fluttering (in high winds) or sagging over years, down to a minimum by having maybe a @ 1/3-in mount, and an @ 2/3-in mounting.

I'm not an engineer, but it would make sense to me to have the panel contact points somewhere in that rough range apart, so the pressure points are going to support the panel with a minimum of deflection potential...

 

[45North]

Depends. How windy is it where you live?
I'm sure there's different design codes depending on your particular location.
Edit: Also depends on the angle as it affects your panels exposure to the wind.

 

[Ampster]

I'm not an engineer, but it would make sense to me to have the panel contact points somewhere in that rough range apart, so the pressure points are going to support the panel with a minimum of deflection potential..

That is a good explanation.
This is probably a situation where conditions in the field might have a bearing on the exact spacing of the rails. It may depend on the roof system and flashing. For shingled roofs the layout of the shingles may determine the exact location of the flashing and fasteners. In the case of a standing seam roof there is more flexibility.
Of course whether the layout is portrait or landscape also affects the distance.

 

[BlueMarblePA]

Thank you for these answers. I will measure the holes and try to optimize placement for maximal security. Since my solar panels will be slightly wider than the roof itself, I want to minimize risk of the panels flying off.

I am outside Philadelphia and do not usually get hurricanes or wind, but it is certain ly possible

 

[Ampster]

Since my solar panels will be slightly wider than the roof itself, I want to minimize risk of the panels flying off.

Some design tools can help you figure out the cantilever amount and the distance that the fasteners can safely be spaced based on some assumptions of wind. A cantilever beyond a roof will require the kind of engineering implicit in those design tools. I use the ones on the Ironridge site since I was using Ironridge rails.

 

[OnGrid]

Some design tools can help you figure out the cantilever amount and the distance that the fasteners can safely be spaced based on some assumptions of wind. A cantilever beyond a roof will require the kind of engineering implicit in those design tools. I use the ones on the Ironridge site since I was using Ironridge rails.

I assume you are putting the panels perpendicular to your roof? If so, do you have gutters? If you do, you want the panels about 6 plus inches from the edge of your roof. I would put the racking about 12" from the edge of the panel. So your bottom racking would be about 18" - 20" from the edge of your roof. Then have the upper rail about 12" or so from the top of the panel.

 

[Rednecktek]

There are also rail mounting posts that have a bolt in the top that goes in the panel hole and gets a nut on the back side, then the bottom of the post interfaces with the racking channel.

 

[BlueMarblePA]

No gutters. I just remeasured and I believe the entire solar panel will be contained within the roof from top to bottom, but it will stick out over the sides by about nine inches each way

 

[BlueMarblePA]

There are also rail mounting posts that have a bolt in the top that goes in the panel hole and gets a nut on the back side, then the bottom of the post interfaces with the racking channel.

I was wondering about that. I think it would make installation more difficult though

 

[Rednecktek]

I was wondering about that. I think it would make installation more difficult though

Maybe, it depends on how the bottom half is designed. If it's a pop-in-and-tighten it's probably not too bad, or you can slide the posts in the rack and just push it down the line as you add more rather than having to walk across the roofline above and below the panels where you might slide off. A stop block at either end would allow you to tighten the string of panels against each other and lock them down rather than trying to get up under each panel.

But that's just my guess. All my panel installs to date have been lumber and drywall screws.

 

[Mike 134]

My solar panels had recommended clamp mounting locations for both landscape and portrait mounting. I bet if you surfed your manufacturers website, you'd find that recommendation.