Putting a garden on the roof

[Matty F]

Let's say, some nice paving stones, and some soil and plants. It doesn't need an engineer's calculations does it?

[Robin]

Might the roof have been designed and built by the same people who did Southland Stadium?

[Adrian]

Nah, little details like that are just bureaucracy and 'elf-an-safety bollocks.

[Tim Watts]

On Sunday 24 November 2013 11:54 Robin wrote in uk.d-i-y:

It will add up to quite a bit of weight - take the slabs, add a volume of water equal to that occupied by the soil (waterlogged) and don't forget snow. Should be easy to get a per-rafter loading figure worst case estimate. Add 50% for good measure plus 100kg point load for when a fat bloke (not you obviously) stands directly over one rafter centre span.

What have you under the roof? 100mmx50mm rafters - over what span and centres?

I'm not saying it won't work - but I would do a sagulation type calculation!

[F]

A supermarket...

[Adrian]

54 Flat Latvians. (Flatvians?)

[Matty F]

Looks like steel trusses about 2 metres high, over a span of about 7 metres. The trusses are bolted on at each end with 6 tiny bolts that seem to have vanished, and the trusses have broken in half. I can't see why they broke in half since there really wasn't that much weight over them.

[Brian Gaff]

Weight bearing calculations I'd imagine would be a given. One does not want a planter complete with wet earth and plants on ones head wile watching the TV after all. Brian

[Dave Liquorice]

The images I've seen show the trusses still attached at one end. So I suspect the 6 bolts sheered, that end of the truss fell, when that it hit the deck the momentum of the truss itself and the roof it was supporting broke it.

Reports indicate that it didn't all go at the same time, the initial collapse was multiple stage but fairly close together. Then another happened once rescuers had arrived and were inside. B-(

[John Williamson]

I suspect a reference to the recent problem in Latvia when a newly installed roof garden caused a supermarket roof to collapes, killing (at the last count I heard) 57 people.

[charles]

Estonia

[Tim Watts]

On Monday 25 November 2013 11:26 charles wrote in uk.d-i-y:

No, Latvia. Zolitude suburb of Riga to be precise. In fact I stayed in the middle of the 3 18 storey tower blocks pretty near to this supermarket when I was travelling there in 1997. Maxima was not built then of course.

[Martin Brown]

In the light of the recent supermarket collapes in Latvia I am surprised you even need to ask this question!

You can get away with houseleeks and mosses that don't add too much weight, but you erode your design overload margin for weight of snow.

[Tim+]

Whoosh! ;-)

Tim

[Nightjar]

It is possible that there had been calculations that showed that the final design worked, but none that took into account how the materials were going to be stacked during construction.

Colin Bignell

[GB]

I'd read of the collapse and assumed it had been badly built. It never occurred to me that somebody had taken a perfectly good design and overloaded it. There was rather a smart design of cobblestones on the part of the roof that collapsed last.

[Tim Watts]

On Monday 25 November 2013 16:05 GB wrote in uk.d-i-y:

It was more than a "green roof" took - the Wikipedia article talks of paving, benches - virtually a "park on the roof".

[GB]

It could have been even worse. It might not have collapsed until there were a couple of hundred people up there having a party.

[GB]

The design would have needed to cover people, planters, 6 feet of snow (this being Latvia), plus a safety margin.

[Nightjar]

Which is where we come to the difference in effect between distributed loads (the finished garden and play area, with or without snow) and point loads, such as a few pallets of paving stones stacked in the wrong spot.

It certainly wouldn't be the first time that something had failed because the loads imposed during construction significantly exceeded those expected on the finished article. I know of at least one part completed bridge that fell into a river because of that. Fortunately it happened overnight, while the construction crew were off site.

Colin Bignell