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Old 10-01-2010, 11:58 PM   #1
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Building a 12x10' shed roofed outbuilding - questions


After the rainy season, I'm planning to construct a 12x10' outbuilding with a simple shed roof (5:12). Id like to make the building inhabitable so it will be insulated and finished.
I'm contemplating ventilation...I should ventilate, right? If so, with an eave soffit, how should the air be vented at the ridge? I found an image from Cor-A-Vent that's a possibility:



I'd like to also make this a "green roof" with soil and plants on top. I'm thinking 2x8 douglas fir no.2 rafters at 24"oc should be sufficient, no? Looking at a span table, they're good to 11'8" with 20psf dead load


Thanks in advance for your advice


Last edited by dwoloz; 10-02-2010 at 04:56 PM.
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Old 10-02-2010, 03:45 PM   #2
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Building a 12x10' shed roofed outbuilding - questions


Another question:

I'd like a healthy overhang, maybe 2' or so, on the 12' side with the front door and am wondering whether I can cantilever it or if I need a support post.

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Old 10-02-2010, 05:41 PM   #3
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Building a 12x10' shed roofed outbuilding - questions


2 x 8 might be too light depending on the amount of soil on the roof. 20 psf isn't a whole lot.
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Old 10-02-2010, 07:16 PM   #4
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Building a 12x10' shed roofed outbuilding - questions


Quote:
Originally Posted by jlhaslip View Post
2 x 8 might be too light depending on the amount of soil on the roof. 20 psf isn't a whole lot.
Hm, I think you're right
Green roofs have a lot of factors like soil media, depth, plants, etc. I'm thinking I will go lightweight with 4" of expanded clay soil media, sedum succulents and some kind of lightweight drainage substrate. The most weight it will see is in a rain with all the material wet

This pdf gives a green roof example of 20psf dead and 30psf live
http://docs.google.com/viewer?url=ht...l%20Design.pdf

This one gives the example of a 26psf dead load in addition to the load of the roof
http://docs.google.com/viewer?url=ht...en%20Roofs.pdf

This one says 15-50 additional dead load for a green roof
http://www.glwi.uwm.edu/research/gen...oofinstall.php



So perhaps 30psf is a more reasonable estimate (if using materials on the lighter side).
This calculator unfortunately only goes to 20psf http://www.awc.org/calculators/span/...rcalcstyle.asp but 2x10s seem safe
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