Proper railing/framing of panels on a motor home roof. Help please.

System

I am preparing to install 3 - 230w panels on the roof of my motor home. I need to understand the correct way to use rails and pedestals to support these panels about 6 inches off the roof surface. I have chosen 6 inches in order to be above my luggage rack system and to help minimize shadows form items in close proximity. I am placing 2 of these panels beside each other. These panels are 39" X 65" and weigh about 44# each. These panels will be placed with the 39" sides perpendicular to the length of the coach. I am thinking of using 2 rails made of 2X2X1/8 inch aluminum angle - each about 82 inches long running under the 2 panels about 12 inches from each end of the panels. These 'rails' would be perpendicular to the long dimension of the panels. These 'rails' would each be supported with 4 six inch pedestals on each of the 2 rails. I have also considered building a frame all the way around each panel but think this may be over doing it and would add more wind resistance. Are rails like I describe above adequate or what would others here recommend? The third panel will be by itself a few feet away form the pair. I plan a similar but smaller setup for this panel. THANKS TED

bluewickedburner

Re: Proper railing/framing of panels on a motor home roof. Help please.

The frames that are part of the panel construction should be adequate. The design end should be less weight, not more. Use individual standoffs because that roof is likely curved.

Just hold that 82" length of angle and you'll see how much it flexes, it isn't going to add much support on a motor home roof. Make sure you include some fail-safe securing hold down in case things go wrong as you drive down the freeway. Better to have a panel banging on the roof or sidewall than spinning through the air behind you, I know someone that experienced just that and you do not have enough insurance to cover what happens after that.

Adding a frame just makes things a lot more complicated than it needs to be. It is very important to make sure you can walk around the panels because believe me, you will need to, it just happens. You're also going to need to lift the panels to clean under them so factor that in too.

System2

Re: Proper railing/framing of panels on a motor home roof. Help please.

Bluewickedburner, Thanks for the information. Your recommendation for some sort of fail safe is the first I had ever heard . What do you suggest for such a fail safe? My planned use of 4 pedestals on each rail along the length of the coach will allow me to place 2 and probably 3 of the 4 on roof joists. I will investigate how much curve there is in the area I plan to mount the 2 rails. I could tie the rails to the mounting plate of the rear air conditioner with a piece of 1/8 inch vinyl coated steel cable as a fail safe. I am planning on triangle cross bracing between the 2 rails to stiffen any front to back or side to side movement.

Comments by all are welcome. TED

bluewickedburner wrote: »

The frames that are part of the panel construction should be adequate. The design end should be less weight, not more. Use individual standoffs because that roof is likely curved.

Just hold that 82" length of angle and you'll see how much it flexes, it isn't going to add much support on a motor home roof. Make sure you include some fail-safe securing hold down in case things go wrong as you drive down the freeway. Better to have a panel banging on the roof or sidewall than spinning through the air behind you, I know someone that experienced just that and you do not have enough insurance to cover what happens after that.

Adding a frame just makes things a lot more complicated than it needs to be. It is very important to make sure you can walk around the panels because believe me, you will need to, it just happens. You're also going to need to lift the panels to clean under them so factor that in too.

bluewickedburner

Re: Proper railing/framing of panels on a motor home roof. Help please.

Whatever you do, DO NOT use the roof joists as supports for solar panels. Here is why:

On a motor home, the roof joists are not there for support but to provide structure for the plywood/fiberglass layer on top but more importantly, to hold the sidewalls inward. Another way to say it - roof joists on a motor home are not load bearing but rather stressed members that keep the sidewalls from falling outward.

Place your support pedestals so that they miss the joists. Drilling into or in any way modifying the joists weakens them and defeats their purpose. I learned this by calling a couple manufacturers specifically about this. That also makes is easier to do hour install. If you have fiberglass roof material, use toggle bolts to hold your supports onto the roof. Drill an appropriately sized hole, put 3M 530 Sealant Adhesive on the bottom of the support and put that down on the roof. Then follow with the toggle bolt. Before that fails your roof will have to rip away.

For a fail-safe you can use a simple cable (covered) attached to both panel frame and one of the supports. Keep it simple. It's purpose is to keep the panel from leaving the roof should the worst happen. The cable can be short. If the worst happens, you'll hear it banging around on top of your roof, giving you time to pull off the road and take care of things. Better than it flying off and hitting whatever vehicle is on the road behind you.

Lay everything out on the roof before using the sealant/adhesive to make sure of locations. 3M 530 gives you about 10 good minutes but after that it is setting pretty fast. The next day you are good to go. You can cover the supports with more of the sealant/adhesive or use 3M Extreme Sealing Tape to insure no water leaks are possible where you did your work. If you follow 3Ms application instructions verbatim, you Will Not have any water leaks where you did your work.

3M Extreme Sealing Tape is not cheap but with solar on a motor home roof, nothing is cheap, or at least nothing should be.

One more thing, panels closer to the center of the motor home (front to back) will experience less vibration and road bumps than panels located over the axles or rear of the rear axle or forward of the front axle.

Good luck

System2

Re: Proper railing/framing of panels on a motor home roof. Help please.

Bluewickedburner, Thanks again for your insight. I have a briteteck rubber roof verses fiberglass. How does this change your fastener recommendation? I plan to fabricate my pedestal feet from 2X2inch aluminum angle and can use pieces long enough to get lots of square inches of roof surface. I was thinking 8 inches for 16 square inches per pedestal. I can turn half of them 90 degrees for added stability. I am thinking that I will use 1X1 inch square tubing for the uprights. TED

bluewickedburner wrote: »

Whatever you do, DO NOT use the roof joists as supports for solar panels. Here is why:

On a motor home, the roof joists are not there for support but to provide structure for the plywood/fiberglass layer on top but more importantly, to hold the sidewalls inward. Another way to say it - roof joists on a motor home are not load bearing but rather stressed members that keep the sidewalls from falling outward.

Place your support pedestals so that they miss the joists. Drilling into or in any way modifying the joists weakens them and defeats their purpose. I learned this by calling a couple manufacturers specifically about this. That also makes is easier to do hour install. If you have fiberglass roof material, use toggle bolts to hold your supports onto the roof. Drill an appropriately sized hole, put 3M 530 Sealant Adhesive on the bottom of the support and put that down on the roof. Then follow with the toggle bolt. Before that fails your roof will have to rip away.

For a fail-safe you can use a simple cable (covered) attached to both panel frame and one of the supports. Keep it simple. It's purpose is to keep the panel from leaving the roof should the worst happen. The cable can be short. If the worst happens, you'll hear it banging around on top of your roof, giving you time to pull off the road and take care of things. Better than it flying off and hitting whatever vehicle is on the road behind you.

Lay everything out on the roof before using the sealant/adhesive to make sure of locations. 3M 530 gives you about 10 good minutes but after that it is setting pretty fast. The next day you are good to go. You can cover the supports with more of the sealant/adhesive or use 3M Extreme Sealing Tape to insure no water leaks are possible where you did your work. If you follow 3Ms application instructions verbatim, you Will Not have any water leaks where you did your work.

3M Extreme Sealing Tape is not cheap but with solar on a motor home roof, nothing is cheap, or at least nothing should be.

One more thing, panels closer to the center of the motor home (front to back) will experience less vibration and road bumps than panels located over the axles or rear of the rear axle or forward of the front axle.

Good luck

bluewickedburner

Re: Proper railing/framing of panels on a motor home roof. Help please.

If you haven't gotten too far into this (cutting aluminum) I am willing to send you a roof mount drawing you can make, accurate for fabrication using the basic tools you already have, just PM me. I'd need a couple days to get it back to you. Include what materials you already have along with the exact brand/model of panels and the model of your motor home would be handy too. You'll have a cutting list, fastener list, and source list where to get some things I spoke about without going bankrupt, then benefit of more than 400 hours of design, research and prototypes. My tracker is one the roof sticking up in the air a little over 9 inches, tracks elevation and azmuith with a 63x41 total panel area and is stronger than any motor home roof.

All of this is much easier than what you read here and you should be up and running in a few good hours.

If you can, use 1x2 instead of 2x2. The long dimension provides more than enough strength and you save 50% of the weight, that is if your budget allows and you're not already knee deep into this. You can use the angle for the feet or supports going to the roof. That will make attaching them quite easy since you won't be going through two walls of the aluminum material. If you through bolt the square tubing it is easy to compress it and things come loose. Where you bolt one piece of aluminum to another you want whatever nut and bolt system you use to be able to take enough torgue for the bolt /nut specs. I used 1/4-20 SS made in the USA stuff. Dont skimp.

As for the roof material, the joisting still provides the same function, I should have explained that before, sorry. I recently had the opportunity to go completely through a major roof modification on a fifth wheel where in excess of 400 pounds of material was being mounted on top on a relatively small part of the roof. The joists were ctirical in holding the walls inward, not the roof up.

What holds the roof up is the plywood which is usually bowed to some degree. Bowing the roof was more important for strength that for letting water run off but few people know that because it seems natural to think of it the other way. Dont worry about the weight on your roof, you walk on it right?

Think of it this way, when you step onto your roof, if you weigh just 160 pounds and walk, all of the weight is on one small spot yet your foot doesn't go through the roof. Your solar panels don't have enough weight to worry about, just avoid doing anything to the joists and you'll be fine. That fail-safe cable isn't there for any other reason that to protect other people, not the panels or your roof.

Don't forget a slight tilt to the panels to allow rain to run off. If you tilt, make sure the lower end is forward or that fail-safe cable will be put to use very quickly. About 5 degrees should do it. You can make the mounts tiltable but then you're climbing on the roof all the time if you travel a lot. The 5 degree tilt can be left as is when traveling.

As always, any advice or drawing I provide are made without warranty or knowing if they are suitable for your specific abilities to duplicate them, so your mileage may vary, okay?

System2

Re: Proper railing/framing of panels on a motor home roof. Help please.

Bluewickedburner, PM sent to you yesterday. Thanks Ted