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helena
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# Posted: 27 Jan 2013 08:50am
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Hi folks, new here. Am in the process of building a small cabin. I've started with burying 6x6 posts to make a 20 square foot square. 
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a bit like that. Anyways, I know I can afford to get walls and a roof on that this year and have a plan of where I'm going to add on to it to create more rooms so plan to put the doorways in to these places now and board them up till I can afford to add those rooms on. This main area will have a single plane (shed) turf roof on it with about a 30 degree slope. I plan to notch in 2x6's into the 6x6 uprights for nailing places for the various additions roof rafters and also notched in 2x6's at floor level which will also serve as attachment points for joists for the main 20 square foot box and for the later additions.
My main concern is avoiding leaky roofs on the additions and are my 2x6's big enough to hold 2x6 joists that will span 10 feet both directions and hold the exterior walls!? Will the 2x6 joists work if I space them close enough together?
Walls will will be made of straw clay infill then plastered and floor will bear the weight of the infill too, so, bearing in mind that these will bear weight of floor joists and the wall infill above them so perhaps I could notch in 2 - 2x6's one on top of the other to form 2x12's all the way around the building at floor level? Any tips?
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MtnDon
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# Posted: 27 Jan 2013 12:34pm - Edited by: MtnDon
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Quoting: helena turf roof on it with about a 30 degree slope.
From the little I've read isn't that a little steep? I seem to recall reading that a 2/12 pitch is about maximum for a green roof; that's about 10 degrees. Thirty degree slope is about a 7/12 pitch for those who relate slopes better to n/12 pitch. I could be wrong as I live in the desert and would have to water my green roof.
Quoting: helena plan to notch in 2x6's into the 6x6 uprights for nailing places
Maybe it's just me but that word picture has me confused. A drawing would help.
What did you use under the 6x6 posts as a footing? How deep> What is the frost depth?
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MtnDon
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# Posted: 27 Jan 2013 12:45pm - Edited by: MtnDon
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Quoting: helena perhaps I could notch in 2 - 2x6's one on top of the other to form 2x12's
Two 2x6's on edge, on top of each other do not make a 2x12. They would be better than a 2x6 alone but it is very difficult to calculate that set up.
The problem is the two 2x6 will slide on each other, much the same as the pages in a pad of paper slide when the pad is flexed. No real easy way to calculate that strength for two boards/planks/beams on top of each other. Trying to lock them together will more than likely cost more than a 2x12 and would still not be as good.
So far it is my opinion that the combination of a turf roof and straw clay infill walls will weigh too much to be supported on the number of piers you have. But that is a casual assessment. It's just that posts 10 feet apart usually are too far apart for regular stick construction. How did you arrive at that spacing?
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helena
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# Posted: 27 Jan 2013 07:08pm - Edited by: helena
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Hi MtnDon, thanks for your replies, very helpful. I believe 2:12 is recommended pitch for a green roof before you have to start putting in supports across the rafters so the turf doesn't slide off. I misquoted. The roof on my sauna I built is 30 degrees, gable roof with turf on. Instead of sheathing used "first cuts" with round side up. Helps keep the turf from sliding and holds a bit of water in the dips for the dryer days we seldom get. This roof will be 3:12. The vernacular roof here is 40 degrees and a foot of turf! designed to shed water quickly and to deal with high wind load i suppose. i'm using thin turf, 3 inches thick max.
Yes, I see what you mean about stacked 2x6's. We wondered about twisting and as you say the bending.
Why have I used 10 foot spacing? Just read in a book of a similar design so, went for that. Have I made trouble for myself?
As it stands, I have 9- 6x6 posts buried about 3 and half feet into the ground, all spaced 10 foot apart in a square. I believe you said something about piers. If so, no piers, just a pole construction type of affair just in case I wasn't clear on that.
Essentially no frost depth, rarely goes below 32F here in winter. Put it this way, I currently have waterpipes lying on the ground and only 4 or 5 days a year will my water freeze on me.
I've read a rule of thumb for floor joist depth is half the span in feet +2. I take it this is for an average stick frame house. that's 7" for a 10 foot span so, 2x8 for good measure. But, as you say still have the weight of walls and some roof weight in between the posts.What if I support the end 2x8's with some concrete blocks or stones spaced underneath? Or what would be a good work around? i've never seen anything bigger "off the shelf" here than a 2x8 so.... How can I work around my span problem? Thanks for your time.
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