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A Shop for Dan #2: Thinking about living roofs

Blog entry by Dan Lyke posted 07-31-2009 11:09 PM 1481 reads 0 times favorited 2 comments Add to Favorites Watch
« Part 1: The state of what is Part 2 of A Shop for Dan series Part 3: Musings on foundations »

I’m still looking for reasonable numbers on roof loads for a living roof. I’ve run across people claiming as little as 7 lbs per square foot per inch of soil, and living roofs in as little as 4” of soil, and numbers as high as 140PSF.

The online calculators and charts for joist calculations (I’m treating this like a floor because a living roof wants to be a fairly flat roof) I’m finding go to a max of 100PSF live load and 20PSF dead load. I’m finding calculators into which I can type a snow load, but my impression is that snow loads are treated like live loads, and what I really want is to calculate a reasonable span (12-16 feet) for a 140PSF dead load and a 20-30PSF live load (ie: someone walking around on the roof).

Of course the other thing I need to do is double-check those living roof weight numbers, because that’s saying I’m going to be supporting (and carrying up a ladder to install) 22.4 tons of material (A human can generate 1/4HP, right? So if the roof is 12 feet high I should be able to do that in 1 hour, 5 minutes and 10 seconds, right?).

And, yes, I will eventually end up having to hire an architect or engineer to sign off on my calculations, but when it comes to my house I’ve run into too much incompetence from professionals to just lob the whole project over the fence to one.

-- Dan Lyke, Petaluma California, http://www.flutterby.net/



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Dan Lyke

307 posts in 2424 days

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jroot

34 posts in 2317 days

posted 06-06-2012 09:03 PM

Amazing, Dan. It should give you good insulation on the roof, and the bonus is a growing area with good sunlight. What are you going to grow up there?

-- jroot

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Dan Lyke

307 posts in 2424 days

posted 06-07-2012 02:18 AM

Our intent was always to steal the California Academy of Sciences living roof list of plants, because our climate is pretty similar to theirs. In practice, I went to the nursery and said “what’ve you got in strawberries and sedums”, and bought a variety. Sedums are a low water coastal succulent plant, and strawberries are… well…

Finally got some plants up there this week, I hope they grow in well. Although I may go spend another couple o’ bucks on more sedums to hold things ‘til the strawberries really take off.

-- Dan Lyke, Petaluma California, http://www.flutterby.net/

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