how to mount solar panel brakcets with screws/lag bolts

[John C]

I am planning to install 2k to 24k solar panel on my 2007 Dynasty Diamond IV. I know a lot of folks are using 3M VHB tape without any issues, I am just not comfortable enough with just tapes.

I don't want to start a debate that the 3M is good enough or not here.

I just want to find out from the guys here in the group if you did use screws or lag bolts, how did you find out where is the steel beam on the roof?

Unfortunately for me, my coach doesn't have thick plywood and the roof is many many layers of foam, luaun board etc. I tried with very expensive metal detector and ended with nothing.

I could not find any  schema which can tell me exactly where is the steel beams (Wish Monaco was still in business).

For my previous coach Thor, they has those readily available. (See attached)

 

Thank you

[Tom Cherry]

WELL as they say... THAT DEPENDS.  The 3M CLEAR VBH is about 20% or so, based on the 3M tech sheets than the thicker black rubber (Emblem adhesive). It is used for door plates...and the package says..  WARNING....you will MAR the surface...

OK...on the ROOF?  I am a Ex Chief Engineer for a fastener company...so I would go with something Mechanical.  My Monaco OEM was screwed down.  BUT, that is also a potential leak point.  Mine has small brackets.  Maybe 1" wide...an angle or bent...and the base (on the roof) was 3/4" or so and it stuck up maybe 1 1/2".

IF I were doing it....easy choice.  I'd use SS Pop RIVETS.  They will stay with you.

BUT....you can use Rubber WELL NUTS (Amazon) like they use on Kayaks...

BUT....This seems to be the best.  I have used them...being an old pop river fanatic.  They worked great holding down hardware on my Kayak.  This one is large Flat Head.  Comes in all styles and heads and possibly SS.  If you can find these in SS, I'd go for it.  Then you screw into the panel.

I LIKE ProFlex and also DiCor 501SWL.  The DiCor levels and spreads more.  It is the closest to the original GeoCel that was used over the fasteners on the roof.

Good Luck...

 

[John C]

3 minutes ago, Tom Cherry said:

WELL as they say... THAT DEPENDS.  The 3M CLEAR VBH is about 20% or so, based on the 3M tech sheets than the thicker black rubber (Emblem adhesive). It is used for door plates...and the package says..  WARNING....you will MAR the surface...

OK...on the ROOF?  I am a Ex Chief Engineer for a fastener company...so I would go with something Mechanical.  My Monaco OEM was screwed down.  BUT, that is also a potential leak point.  Mine has small brackets.  Maybe 1" wide...an angle or bent...and the base (on the roof) was 3/4" or so and it stuck up maybe 1 1/2".

IF I were doing it....easy choice.  I'd use SS Pop RIVETS.  They will stay with you.

BUT....you can use Rubber WELL NUTS (Amazon) like they use on Kayaks...

BUT....This seems to be the best.  I have used them...being an old pop river fanatic.  They worked great holding down hardware on my Kayak.  This one is large Flat Head.  Comes in all styles and heads and possibly SS.  If you can find these in SS, I'd go for it.  Then you screw into the panel.

I LIKE ProFlex and also DiCor 501SWL.  The DiCor levels and spreads more.  It is the closest to the original GeoCel that was used over the fasteners on the roof.

Good Luck...

 

The question is I need to find a mounting point for my 1/2" lag bolts to the roof.

The 1/4" plywood and luaun board is not strong enough for my lag bolts

[DavidL]

To find roof trusses, remove some cover in the interior (light/ vent /fan) and try to find the truss from the inside and measure from a visible reference point where it is.  Then, most are 16" on center.  See if you can verify that from the interior as well.  On a cool moist morning, you might see the trusses in the dew pattern.

[tmw188]

I think trying to find the roof rafters are going to turn into a time consuming mess. If you have a fastenal near you or go on their website and look at different anchors. Maybe something like this as a start.  Something that can reach thru and then expand with a #10/24 or up to a 1/4-20 threaded anchor. Test it out on a OC of Luann 

[John C]

1 hour ago, DavidL said:

To find roof trusses, remove some cover in the interior (light/ vent /fan) and try to find the truss from the inside and measure from a visible reference point where it is.  Then, most are 16" on center.  See if you can verify that from the interior as well.  On a cool moist morning, you might see the trusses in the dew pattern.

No sure about "see trusses in the dew pattern"on a cool moist morning.😀  

Open the A/C vent is definitely a great idea because there are so many of those, will try it tomorrow.

Thank you!

[timaz996]

I don’t know if Monaco change the way they made the roofs but on my coach I used one and a half inch self tapping screws, and Daycor to seal the mounting points of my solar panels. Four panels have been up there for seven years and the other four on one year and I have been driving 60 miles an hour in some very wicked winds Without any problems. Four of my panels are set up to tilt so they are mounted with aluminum angle iron with four screws at each end. The other four stay flat, but they end up being mounted with the same number of screws. Like I said, no issues . I have speakers in the ceiling, and if you drop them down, you can see into the cavity that the air conditioning ducking runs through in between the roof and the ceiling and my screws peek through about a quarter inch.

Edited April 30 by timaz996

[vito.a]

I used both 3M VHB and #10 stainless screws. Then covered the screws with Dicor. 

My factory mounted panel was installed the same way.  

If the luan/fiberglass roof is strong enough to hold my weight it's strong enough to hold a solar panel. 

Edited April 30 by vito.a

[Paul J A]

Some folks have had success using eternabond tape on the roof,  under the foot of the panel mounting bracket, another layer on top of the foot.  Do a bench test. You will be amazed. Make the foot as large , or size/shape you want .

[Georgia Mike]

John, I have the same roof as you and have 3 panels mounted. I just used stainless 1 1/2 screws and Dicor and didn’t worry about hitting trusses. I pre drilled the hole and forced Dicor in it then applied plenty of Dicor on the bottom of the brackets before attaching them. I then applied more Dicor on top. On my previous Motorhome I installed panels the same way and they were exactly as I installed them when I sold it after 11 years.  

[RNMCBR]

I’ve used 3m VHB on two different coaches over about 12 years. I find it to be more than adequate for holding down solar panels. I have done a lot of driving in very high winds in the southwest with no indication whatsoever of any of my mounts coming loose. I currently have 12 100Watt panels mounted with it. I am using 4 “L” brackets per panel with a footprint of 2 square inches VHB each, and with Dichor sealant over the top to seal the attachment. I have tested the bond and agree with what AM solar told me: “you will likely tear a hole in your roof trying to pull the panels off”. 
3m also makes a primer that will accelerate the cure of the adhesive. I used that for the last 4 panels I installed and think it helped develop a good bond. 
I know some folks would rather use fasteners and I am sure that is as good or better than the 3m tape. But I don’t want to have a bunch of screw holes penetrating my roof especially since they only go into the thin luan underlayment. 
Each person should decide what attachment they prefer, but I just wanted to share my experience with the VHB tape. 
Good luck
 

[Tom Cherry]

2 hours ago, RNMCBR said:

I’ve used 3m VHB on two different coaches over about 12 years. I find it to be more than adequate for holding down solar panels. I have done a lot of driving in very high winds in the southwest with no indication whatsoever of any of my mounts coming loose. I currently have 12 100Watt panels mounted with it. I am using 4 “L” brackets per panel with a footprint of 2 square inches VHB each, and with Dichor sealant over the top to seal the attachment. I have tested the bond and agree with what AM solar told me: “you will likely tear a hole in your roof trying to pull the panels off”. 
3m also makes a primer that will accelerate the cure of the adhesive. I used that for the last 4 panels I installed and think it helped develop a good bond. 
I know some folks would rather use fasteners and I am sure that is as good or better than the 3m tape. But I don’t want to have a bunch of screw holes penetrating my roof especially since they only go into the thin luan underlayment. 
Each person should decide what attachment they prefer, but I just wanted to share my experience with the VHB tape. 
Good luck
 

Great information.  Thanks.  Just be aware that there at least TWO different types of the "Generic 3M VHB" double stick. The spec sheet says that the thinner CLEAR has better "peel" or holding strength. However, it is recommended for flat surfaces....where the thicker "black" emblem tape might give a better bond of a slightly rougher surface.

Personal experience, like Roy posted.  If you ever had a factory double sided gasket peel off.  Use WD-40 on both the MH and the rubber gasket and peel off all the OLD or residual adhesive.  Sometimes a little Acetone will help.  It will not hurt, on a cloth, either surface.  Then... THOROUGHLY wash with a soap like a little Dawn in a bowl....rinse and dry.

THEN...  Right before you apply, use a cloth with a little acetone on both surfaces.  This acts as a primer in that it activates the surfaces.  Then apply and mount.  It will HOLD as long, presumably, until the proverbial bovines come home.

I would use that technique, including the acetone activation, on any solar bracket that I mounted.  

Good Luck.

[Benjamin]

15 hours ago, John C said:

No sure about "see trusses in the dew pattern"on a cool moist morning.😀 

The roofs are typically insulated, but poorly, as in very little attention is given to eliminate thermal bridging.  So a metal framed wall will perform terribly, especially if it's aluminum with aluminum skin.  Even with above average insulation, the thermal conductivity shows through dew as it dries at different rates.  I've seen the nails under vinyl siding with dew, rafters and finished attics on roofs with snow, even purlins under metal roofing from the paint fading, still don't know how that one works.  

You don't need a cool moist morning either, if it's cool outside, then have the heat on inside and mist down the roof before dawn, or in the shade on a still day.  If it's hot outside, you can try it with the AC on inside. 

I'd reconsider the 1/2" lag bolts, that would take at least 1" of plywood plates to hold a bolt that big.  More and smaller fasteners is more appropriate. 

[Mark B]

I used 3M marine adhesive. It's been three years with no issues. I followed the directions and proper surface preparation. I also used panel brackets from eBay.  I have two 350-watt residential panels in series. I applied the adhesive to the bottom of the brackets and followed up around the edge to seal them.

[John C]

21 hours ago, John C said:

No sure about "see trusses in the dew pattern"on a cool moist morning.😀  

Open the A/C vent is definitely a great idea because there are so many of those, will try it tomorrow.

Thank you!

Just opened the vent, unfortunately I can't see much, the insulation above is not movable.

Guess I will have to wait for cool moist morning, but the chance of see that kind of weather in So Cal right now is going to be very hard now.🙁

21 hours ago, timaz996 said:

I don’t know if Monaco change the way they made the roofs but on my coach I used one and a half inch self tapping screws, and Daycor to seal the mounting points of my solar panels. Four panels have been up there for seven years and the other four on one year and I have been driving 60 miles an hour in some very wicked winds Without any problems. Four of my panels are set up to tilt so they are mounted with aluminum angle iron with four screws at each end. The other four stay flat, but they end up being mounted with the same number of screws. Like I said, no issues . I have speakers in the ceiling, and if you drop them down, you can see into the cavity that the air conditioning ducking runs through in between the roof and the ceiling and my screws peek through about a quarter inch.

I believe the older one do have thick plywood on the roof...

6 hours ago, Benjamin said:

The roofs are typically insulated, but poorly, as in very little attention is given to eliminate thermal bridging.  So a metal framed wall will perform terribly, especially if it's aluminum with aluminum skin.  Even with above average insulation, the thermal conductivity shows through dew as it dries at different rates.  I've seen the nails under vinyl siding with dew, rafters and finished attics on roofs with snow, even purlins under metal roofing from the paint fading, still don't know how that one works.  

You don't need a cool moist morning either, if it's cool outside, then have the heat on inside and mist down the roof before dawn, or in the shade on a still day.  If it's hot outside, you can try it with the AC on inside. 

I'd reconsider the 1/2" lag bolts, that would take at least 1" of plywood plates to hold a bolt that big.  More and smaller fasteners is more appropriate. 

The 1/2" lag bolts are for the trusses, not for the 1/4" plywood. Yes you are right, if I am not hitting the trusses, I will definitely use much smaller fasteners.

Unfortunately Right now or in next 6 month in So Cal, no sure I am going to get any moist at all.

[timaz996]

If you take out one of your speakers in the ceiling, you will be able to see the gap that your air conditioning duck runs through. You’ll be able to see each side on either side of the AC duct I believe the gap is about 2 1/2 inches high. 

[John C]

33 minutes ago, timaz996 said:

If you take out one of your speakers in the ceiling, you will be able to see the gap that your air conditioning duck runs through. You’ll be able to see each side on either side of the AC duct I believe the gap is about 2 1/2 inches high. 

Too bad it is sealed on all sides!

[timaz996]

Wow, that is nothing like mine. These coaches are truly snowflakes.

[Twomed]

3M 5200 and a 1 inch rivet through 1/4 inch aluminum angle brackets....4 panels 600 watts 12 years...110k miles never garaged...still tight.  😄

[Tom Cherry]

9 hours ago, timaz996 said:

Wow, that is nothing like mine. These coaches are truly snowflakes.

YES....  They do seem to be "unique".  However, from spending half of my career in "LINE" manufacturing and having to retool or make revise over 100 stations for a model year change...  IT HAPPENS. 

If you really want to understand the "construction" of your motorhome, the best resource is to download from Monaco or Holiday Rambler the "Sales Brochure".  That discusses, maybe vaguely, the construction of the walls and floor and ceiling.

Almost understand the evolution of manufacturing.  As time passed, there were more advances in how to reduce costs.  I worked in a boat factory during the summer...  We always "laid up" the hull using different layers of fiberglass and also type (Mat, Rovin Wovin and Cloth).  The owner went to a show and bought a "CHOPPER GUN".  It cut fiberglass strands and spit them out impregnated with resin. One man could, properly trained, do the hull in maybe 3 hours for a small fishing boat compared for maybe a day or so with 2 guys. Structurally, based on testing, the chopper gun method was stronger.  THUS....we converted...

I don't pretend to be the expert on many of the "construction" details...but I had to repair a "major dent and void" in the underlayment of my BED slide.  Chris Throgmartin was just testing the Guardian plates and had never seen my failure. We talked... I cut a small "hole" and cored the bottom.  He consulted with a friend that worked in the Elkhart factory.  We both learned about how the floor was laid out in a grid with "perlines" for strength and such...  They had, memory of what I was told, a large laminating operation where the sandwich was two layers (top and bottom) and then the grid or perlines randomly spaced and it was then foamed.  I THOUGHT that maybe it was a "Vacuum Forming" operation....

That was way different from the early days were the panels were closer to "residential" construction.

YES...one never knows what to expect in any exterior surface....  BUT the true "SNOWFLAKE" is a MH built by Crew A and the one behind it built by Crew B...  They are identical...all the "STANDARD RUN" items....exactly the same "Build and MSRP" Sheet... save color.  ONE MH will start, with the Chassis Battery Disconnect OFF...  The OTHER....NOPE...  We have just had a topic that delved into that very subject.  

 

[wamcneil]

On 4/29/2024 at 7:51 PM, John C said:

The question is I need to find a mounting point for my 1/2" lag bolts to the roof.

The 1/4" plywood and luaun board is not strong enough for my lag bolts

Good grief. 1/2” lag bolts? Are you mounting solar panels???  
Or building a deck up there???

[lotosrggp1]

Instead of trying to use small mounts on the roof and adding more places to leak I plan on using Superstruct attached with an appropriate 3M double sided adhesive. Lots of surface area that should never come loose. I plan on using the taller Strut to allow for better airflow to keep the panels as cool as possible. I do tend to overbuild.

[wamcneil]

On 4/29/2024 at 7:31 PM, John C said:

...I don't want to start a debate that the 3M is good enough or not here...

Good luck with that. 🤐

[Dean Bennett]

I’ve had solar for over 20 years on the same MH (2000 Windsor). Over 2,000 watts worth over the last 10 years. I use #14 x 1” Stainless screws:

https://www.amazon.com/Stainless-Steel-Phillips-Screws-Tapping/dp/B08V1PWTSJ

 

I pre-drill about a 1/8” hole, force Dicor into the hole and leave a good-sized puddle on the roof. Set the bracket in the puddle, install the screw and lightly tighten it then, mound more Dicor (NON-self-leveling) over the screw-head and the top of the bracket.

I pre-install the brackets on the solar panel. Then I set the panel in place and get all of the brackets adjusted for tilt and flushness. When I’m happy with the placement, I use a sharpie to mark the drilling locations.

I use 4 brackets per 200W Panel. I’m not a slow driver and we seem to drive on a lot of very-windy days with no attachment or leaking issues. I use adjustable-height brackets so you can tilt the panels enough so water does not pond (as much) on the panels. This also allows for aligning the base of the backet with the tilt of the roof making the contact-patch flush. I was getting these brackets from rvsolarstore.com.

I use good UV and heat rated split wire-loom to wrap the wires and use the same process to attach the cushioned P-Clamps holding the wire:

https://www.delcity.net/store/5:8%22-UV-Resistant-Split-Loom/p_811416.h_811422

 

Use a good combiner box like the one from AMSolar:

https://amsolar.com/shop/roof-cable-management/roof-mount/20-roof/

[John C]

6 hours ago, wamcneil said:

Good grief. 1/2” lag bolts? Are you mounting solar panels???  
Or building a deck up there???

I thought it was 1/2", just looked at again, I believe it is 3/8", that is how I did it on my previous coach.

Maybe a little overkill...

4 hours ago, lotosrggp1 said:

Instead of trying to use small mounts on the roof and adding more places to leak I plan on using Superstruct attached with an appropriate 3M double sided adhesive. Lots of surface area that should never come loose. I plan on using the taller Strut to allow for better airflow to keep the panels as cool as possible. I do tend to overbuild.

That is what I am planning to do if I can't find those trusses.