Roof top Solar Panels 1

Scans will only tell you part of the story - the where. They'll struggle to give good depths or sizes of the bars. Every time I've done something like this (no solar panels, but occupancy changes, construction loading, etc.) we've done scans and cores so we know spacing, size, and depth of bars.

That makes a lot of sense, we had a demonstration from Hilti and it seems like their scanner can do a decent job of getting bar size and depth but that its not perfect so cores would help fill in that info.

What orientation are the solar panels? Flat to the roof, sloped to the roof? What are your concerns, solar panels are very light, especially compared to concrete, could the IEBC be used by chance to show you are barely increasing the stresses?

Yes what is the concern if it's a concrete slab that is otherwise performing satisfactorily? Solar panels are generally LESS than the minimum live load for roofs.

The intention is for the solar panels to be tilted and installed with a ballasted rail system. Also with the NBCC the snow load is specified to be increased due to drifts around the panels.

The dead load of the concrete roof is likely an order of magnitude higher. And like other have said the weight of the panels themselves are likely less the the minimum live load. I really wouldn't be fussed. If it is structurally unsound to be installing solar panels on the roof then it probably isn't structurally sound to allow workers on the roof to do the testing you want.

As a side note, here in Australia we are now requiring PEMB type buildings which normally have very light roofs to be built with allowances for solar panels of 0.15kPa.

Combining the increased snow load from the design code with the new one, and the increased weight from the solar panels, the factored load on the roof increased from 8.1 kPa to 10.2 kPa. This is taking into consideration the reduced factors that the Canadian code allows for buildings that have shown successful past performance.

I've run the calculations with Canadian code and for tilted solar panels your wind uplift will be hefty. The blast system ended up being large which adds a tons(literally) on the roof. 0.9DL+1.4W
Then 1.25DL+1.5SN really messed up the roof.
So careful...

Yes, I havent been provided with the ballast system that is planned but the rough numbers indicated there would be similar issues. While I dont want to tell the client that it isnt feasible without having calculations to back it up I am hesitant to expect that it will work out and hence am curious how there are so many local installers that dont seem to be doing structural reinforcing.

As I have done many ballast and non-ballast solar system designs many years ago, including roof checks, I suggest you get the final ballast weights and that they use a company that has a ballast system that relies on wind tunnel testing as many of the larger outfits that make racking do. There is a chance that wind could be lower in many zones based on the wind tunnel testing they have for various systems. This also allows their ballast loads to be reduced significantly compared to ASCE style wind calculations. For snow I would consider drift, however also consider that I don't believe you are typically changing the net snow loading on the roof, only allowing it to move around, so with analysis you could find it may still be ok.

Start with telling them they need to provide you with ballast design by the racking manufacturer using a system that has wind tunnel studies to have the best chance to work.

Struct123ure said:

I've run the calculations with Canadian code and for tilted solar panels your wind uplift will be hefty. The blast system ended up being large which adds a tons(literally) on the roof. 0.9DL+1.4W
Then 1.25DL+1.5SN really messed up the roof.
So careful...

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Is it really that bad?

If there are uplift pressures under the panels then there would be similar opposite pressures downward on the roof that mostly cancel out. I find it hard to believe that solar panels are going to significantly change the NET increase in uplift pressure. Also my GUT feeling is that you are not going to have uplift challenges on a concrete roof. But I'd happily be disputed on that GUT feeling.

Regarding snow loads. I have no experience there, but I can see that panels if not appropriately installed could drastically increase the potential loading.

My 2cents.

human909 said:

I find it hard to believe that solar panels are going to significantly change the NET increase in uplift pressure.

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Going from a flat roof to many rows of open frames in a sawtooth layout will most definitely change roof uplift, however as you have said, probably not a big concern for uplift itself, the issue is in the fact that the OP said it's a ballasted system, which means no physical attachment and they add trays of concrete blocks, gravel or other weights to weigh down the panel racking to it doesn't fly off the roof in a storm, couple this with it having to resist both uplift, overturning and sliding, the ballast can get quite heavy when designed properly, easily increasing your roof dead loading. Now having said that, in the past we almost always found a way to make it calc out, and we were using much lighter roofs, never had a concrete roof to check.