Roundhouse.. roundwood or timber frame

Hello,

I am considering a roundhouse build. A decagon, 1.75stories. It would be 32ft diameter. 8/12 pitch, metal roof in heavy snow country.
I  have a 16ft capacity bandsaw mill, a woodlot with mostly hemlock, and a 3t excavator.

Given my roof frame design I would need several pieces longer than 16ft. 5x at 23ft for primary rafters and 10x at 21ft for secondary rafters.

I'm stuck between going with roundwood or timbers. Each have implications and concerns. I shall go into more details..

Given my plans/strategy, the implications are as follows:
For roundwood, I'd have to either go hemlock and log myself, which means new roads + inexperienced logger/road builder... or
Hiring a logging truck to deliver 5x 23ft 10in+dia small end and 10x 21ft 8in+dia small end, fairly straight + excess for firewood, which would mean monies.. but may be worth it.

or

for timbers
Felling hemlock by the site, taking a couple passes with a chainsaw mill, then lifting onto the mill and rigging up a system to mill the longer lengths.

With the timbers, I can get more out of the larger, 22in+ hemlocks at the base. But, it seems like a lot of work to pre-mill on the ground and rig a system to push the log through with the mini excavator. I think I can do it with two passes per length on chainsaw mill, and 6 passes/length on the rigged bandsaw mill, and it would require harvesting 7-8 trees, and no new road infrastruture.

I'm concerned about strapping the roof with roundwood. I imagine the curves of the roundwood would make the roof less uniform and impact snow-shedding performance on the metal roof. Is this an issue for people with knowledge/experience?

With the timbers, I can get more out of the larger (22in+ hemlocks at the base), but it seems like a lot of work to pre-mill on the ground and rig, when I could do other structures by keeping things within the bandsaw capacity and mini exc capacity.

Other info:
I'd like to build a smaller version with the same framing for a ~14ft dia duck coop in the early spring, 2025.
I'd be cutting/seasoning the logs/timbers for use in 2026. I'd be doing 14x4 for primary rafters, 14x4 for secondary, 3x14 for Tetiary, and 2x8 for bottom half spanners secured ~half way to primary/secondaries.  
I have a machine for clay-chip making and lots of clay, will be infilling walls 12" claychip.
Building code people generally stay away, but I'd like to over-build regardless.
Advice on my current plan or advice in general is appreciated. I do have a rough sketch of the framing plan if people think that is of use I can upload/share. I took the basic design from "The Maloca" seen here: https://sentinelbc.ca/stay-with-us/#&gid=1&pid=sentinel-05515-jpg . I adapted it for 10sides, and increased the slope + will be adding a tensioned steel cable around the perimeter.

I figure I'll just post the roof framing now as I suspect it will be requested information for providing advice and general feedback. I hope it is legible enough, I'm not sure if perhaps there is a way to zoom in? I'm not the greatest with tech this way.

https://tinypic.host/image/roundhouserafters.2QMv4v

Neat project! I guess I'll propose some other ideas just in case you hadn't considered them...

How much would it cost to buy the timbers and have them delivered?  Maybe getting dry timber that's graded/stamped might be worth considering?

What about a different roof rafter layout that can use 16' timbers?  Perhaps with a few posts?  Or a hogan style?

I would recommend to start with something smaller to get the feel how it's going.
Large polygonal structure will be more difficult than large rectangular, and large rectangular more difficult than small rectangular.
If I had to choose I would go for milled timbers. Round logs still need to have the bark removed and after that they are still round, and potentially crooked. Milled heavy timber adds aesthetics to the structure.

Mike Haasl wrote:Neat project! I guess I'll propose some other ideas just in case you hadn't considered them...

How much would it cost to buy the timbers and have them delivered?  Maybe getting dry timber that's graded/stamped might be worth considering?

What about a different roof rafter layout that can use 16' timbers?  Perhaps with a few posts?  Or a hogan style?

Thanks for the input.

I did not consider buying the timbers, although as per your suggestion I have sent out for a quote. If it seems decent I may send out a few more. This would also allow me to get d. fir, which would be easier to work with and stronger than hemlock.

That is the first time I've seen hogan style. Very cool. I wonder if it would make insulation of the roof challenging? I assume it also would be difficult to generate a slope that easily sheds snow? I do live in a cold climate(zone 5) that has 4-5ft+ of snow per winter. I was planning to do 12-14" of cellulose in the roof.

I would have played around with an outer+inner circle design and attaching rafters that are 16ft. This would be more feasible if I was starting from scratch. In my current situation, it would be challenging. I have already built the floor for this build, and it is only 2x6fir. I currently have a 30', insulated w/ hardwood finished floor(except for the center 5ft diameter). My 30' yurt is currently supported by this floor. The idea was to stem wall around the yurt, use the yurt as scaffolding and scaffold a high central platform to get the frame + roof. Put metal on it. Then, live in the yurt for the winter with the roof overhead. Year2, take down the yurt, install central post and members for the second floor, do electrical, insulate+extend floor to edges of new stem wall, infill the walls, and finish inside of roof + insulate.

Cristobal Cristo wrote:I would recommend to start with something smaller to get the feel how it's going.
Large polygonal structure will be more difficult than large rectangular, and large rectangular more difficult than small rectangular.
If I had to choose I would go for milled timbers. Round logs still need to have the bark removed and after that they are still round, and potentially crooked. Milled heavy timber adds aesthetics to the structure.

Yes, I imagine it will be a challenging build. I am looking to break it up into 3 years.

I did mention I was planning to build a 14ft duck coop with the same framing. This will be used as a way to test it out and sense difficult scenarios to anticipate for the future build.

If I was going for round logs I would go for the 7" grinder+debarking tool. It will still take time, and I think they would still be prone to be crooked and or continue curing after a year. I'm leaning more towards the timbers, even though the timbers will not be visible as I will be using 12" of claychip for walls, and 12" of insulation in the roof.