How to mount panels onto Fiber Cement sheets?

[Ben Harper]

What's the recommended way of mounting solar panels to a fiber cement roof (sheets, not tiles)?

I assume whatever screws one puts in need to penetrate into the wood, because the fiber cement is not strong enough. Also, it seems desirable to get the screws to mount to the main roof beams, instead of just the purlins, because the purlins are usually just nailed into the main beams. If this is the case, how do you locate the main beams from the outside?

I live in the Cape Town area and I enjoy doing these kinds of things myself, so looking for a place where I can purchase the necessary stuff, and some recommendation on suitable equipment.

I've attached a picture of the roof.

Thanks!

[Virwat]

Just in purlin should be fine.

You should first measure the distance between the purlins as it is now, then compare it to the panels mounting specs.

You gonna love working on that angle: grin

[Ben Harper]

I measured the bolts currently on the roof, and they're 100cm apart, and I assume that that roof is bolted into every purlin.

What is the bolt called that you've posted here, and do you know where I can buy them?

Also, I'm guessing that you attach a rail onto that bolt, and then the panel onto the rail?

And yes, the angle is menacing. Just steep enough to slide off. I'll build a hooked ladder for the job.

[Garthox]

9 minutes ago, Ben Harper said:

I measured the bolts currently on the roof, and they're 100cm apart, and I assume that that roof is bolted into every purlin.

What is the bolt called that you've posted here, and do you know where I can buy them?

Also, I'm guessing that you attach a rail onto that bolt, and then the panel onto the rail?

And yes, the angle is menacing. Just steep enough to slide off. I'll build a hooked ladder for the job.

They are roof hanger / hanger bolts

Hanger bolt

I'm planning to do the same into the big 6 nutec roof sheets here by me.

 

[Ben Harper]

So what does one attach onto the hanger bolts?

Does one place a rail onto the hanger bolts, and then mount the panels to the rails, or do the panels go straight onto the hanger bolts (with some kind of clamp thing obviously)?

[Ben Harper]

I'm going to try to answer my own question here.
 

1. Hanger bolts about 1m apart

2. Attach rails onto the hanger bolts (2 rails per panel). Rails mounted horizontally, if panels are portrait

Drill horizontal holes into the rails to attach to the hanger bolts

3. Use mid clamps and end clamps to bolt the panels down to the rails
 (mid clamp)

4. Place end caps to cover the rails

Does that sound right?

 

[Sidewinder]

31 minutes ago, Ben Harper said:

Drill horizontal holes into the rails to attach to the hanger bolts

This does not make sense... The rail has a goove on the side where the horizontal bolt can slide/fit into and then gets tightened. 

 

Also the hanger bolt spacing will be dependant on your truss spacing (normally 700mm), please don't bolt the hanger bolt into brandering etc, unless you want to collect your broken panels some distance away, special when the Cape Doctor comes and visits, even when you don't live in CTN.

Just my thoughts..

[Virwat]

Stainless Steel T-Bolt slide into the rail ( I assume that rail you posted is Renusol ) and fastened to the L-Bracket on the Hanger Bolt.

+- R6.50 for a bolt, washer and nut. (Bonanza Technologies - Roberto helped me out here, What a pleasant Italian chap)

Edited November 30, 2023 by Virwat

[Ben Harper]

Thanks - I understand now how the T-Bolt attaches to the rail.

@Sidewinder - are you suggesting that I ensure the bolts go all the way down into the main roof beams?

The house is in Pringle Bay, so wind is indeed a serious issue.

If the bolts need to go directly into the main beams, how on earth does one locate them from the outside?

[GerhardK83]

1 hour ago, Ben Harper said:

If the bolts need to go directly into the main beams, how on earth does one locate them from the outside?

@Ben Harper Does the ceiling run parallel to the roof or is there a space between the ceiling and the roof?

[Virwat]

Just curious.

What is the difference between the hanger bolt screwed into the purlin or the truss.

If it wants to pull out because of wind, it will.

Purlin height is 75 mm, Use hanger bolt that screw in as deep as possible. (various lengths available)

Main beams must overhang outside by +- 500mm

(maybe covered by nutek or similar. Also, if there are gutters, their brackets most probably will be fastened to the beams)

[Ben Harper]

The ceiling is parallel to the roof beams - you can clearly see the main trusses from inside the house.

Thanks @Virwat - that makes total sense that one can see the beams sticking out the bottom of the roof. I'm not here right now, but that makes perfect sense.

[Ben Harper]

3 hours ago, Virwat said:

What is the difference between the hanger bolt screwed into the purlin or the truss.

If it wants to pull out because of wind, it will.

Purlin height is 75 mm, Use hanger bolt that screw in as deep as possible. (various lengths available)

Now that I think more about this, you must be right. I was thinking that the purlins might be so weakly attached to the trusses that the purlins would pull out. But that is ridiculous, because then the whole roof sheet would rip out. There must be hurricane brackets between the purlins and the trusses.

[Sidewinder]

The T-bolt should be part of the hanger bolt. As mentioned, if it is a Renusol part, then yes. I've used the Eco roof brackets on my (latest) install, and they came prepopulated with the T-bolt. If not, then Roberto is your answer. I've also bought many inverters from him before.

Many years ago I did my own installation. Simular situation as you, as i couldn't locate the trusses. So i removed the screws (luckily they were hexnuts) where the roof sheets were fastened to the purlins. I replaced them with new longer screws. As you can see from my markings in yellow, my screw spacing was much tighter. (For obvious wind reasons).

The mistake I did was not to use a hanger bolt, as that would have given me a greater height of the pv panel to the roof, for better ventilation.

If I was you, I would get the longest hanger brackets and try and mount the mounting rail as high as possible (to increase the gap between roof and PV)

, 

[Sidewinder]

@Ben Harper

In case you don't have it, here is the complete installation manual for the hanger bolt.

If you need a bigger one, Segensolar do sell a M12 version. Alternative would be to look for an equivalent on the KD solar range.

Renusol Hanger bolt manual.pdf

[Ben Harper]

Thanks @Sidewinder, that is very useful.

Mounting the rails straight to the roof looks like it would save a few R, but why do you say it's good to have ventilation between the panels and the roof?
I don't know anything about aerodynamics, but my gut tells me that a smaller space between panel and roof would produce less wind force trying to pull the panels off.

[Sidewinder]

Yes, less space = less chance of the Cape Dr. to take your panels!

The down side of less space is poor ventilation, and poor ventilation = rising temps of the PV.

High PV temps = lower PV production. So it's a tradeoff. 

If you can get the gap as high as possible, within the limit of the equipment you have/going to use, then just make sure it is over engineered. e.g. adding additional/(M12 vs M10) hanger brackets. Saving a few 100 R's is just not worth it, especially down in WC region.

[Sidewinder]

Another way of looking at this, could be to see if the prevailing wind direction over your property is across the panels. i.e the wind/breeze can enter that gap between the roof and the PV panel.

If not, then increase the height to improve circulation.

[Virwat]

29 minutes ago, Sidewinder said:

@Ben Harper

In case you don't have it, here is the complete installation manual for the hanger bolt.

If you need a bigger one, Segensolar do sell a M12 version. Alternative would be to look for an equivalent on the KD solar range.

Renusol Hanger bolt manual.pdf 634.47 kB · 2 downloads

..... but sir, we don't sell to non-account customers!....

[Ben Harper]

39 minutes ago, Sidewinder said:

Yes, less space = less chance of the Cape Dr. to take your panels!

The down side of less space is poor ventilation, and poor ventilation = rising temps of the PV.

High PV temps = lower PV production. So it's a tradeoff. 

If you can get the gap as high as possible, within the limit of the equipment you have/going to use, then just make sure it is over engineered. e.g. adding additional/(M12 vs M10) hanger brackets. Saving a few 100 R's is just not worth it, especially down in WC region.

The mounting bill is already looking steep, but I'll follow this advice.

[Thunderdolt]

This is for slate roof but will probably do what you need.

https://www.solarwaysuppliers.co.za/product/slate-roof-bracket-2/

Complete kit!

[GerhardK83]

8 hours ago, Ben Harper said:

The ceiling is parallel to the roof beams - you can clearly see the main trusses from inside the house.

@Ben Harper thanks for the feedback, it sounds interesting that the ceiling is parallel to the roof beams with the main trusses visible from the inside of the house, it would be interesting to see a photo or two of the inside with the trusses and ceiling.