Author Topic: Round Cob Cottage w/ Sod Roof in MI w/ Video  (Read 597 times)

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Offline Ernest T. Bass

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Round Cob Cottage w/ Sod Roof in MI w/ Video
« on: November 17, 2017, 08:21:19 AM »
Hey peeps! Some of you might remember me as that wacky kid who spearheaded a cob/cordwood homebuilding project 10 yrs ago. Well, my younger sister is following in my footsteps and has recently finished a cob studio project that I thought you might find interesting..

I just did a short 4min film for a competition, featuring her and her project: https://community.zooppa.com/en-us/contests/everyday-humans-2017/submissions/mary-lund

There's a simple post-and-beam frame that supports the reciprocal roof buried in the wall. The walls are actually cordwood with earth plaster covering everything; the cordwood offers more insulation than solid cob, and the earth plaster is great for combating cordwood's notorious air-infiltration problems, as well as eliminating the need to tuck-point and use perfectly dry wood. The foundation is stepped earthbags on a slope; shallow footer for our climate, frost-protected with foam and a washed gravel footer. A couple winters so far with no movement.

There was certainly a lot of experimentation in the build, but some of these methods seem to be working quite well.

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Offline Don_P

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Re: Round Cob Cottage w/ Sod Roof in MI w/ Video
« Reply #1 on: November 17, 2017, 03:15:03 PM »
Beautiful! I've wondered what you were up to.
Comments on the roof? How difficult was it, tough to sheath or no?

Offline MountainDon

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Re: Round Cob Cottage w/ Sod Roof in MI w/ Video
« Reply #2 on: November 17, 2017, 07:00:37 PM »
I like the light spots through the wall... the glass bottles and interior tree design.
Just because something has been done and has not failed, doesn’t mean it is good design.

If you didn't have the time or money to do it right in the first place, when will you get the time and money to fix it?

Offline Ernest T. Bass

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Re: Round Cob Cottage w/ Sod Roof in MI w/ Video
« Reply #3 on: November 18, 2017, 01:03:14 PM »
Yeah, Mary was a lot more artsy and detail-oriented with her design than we were with our house. :)

The roof was a pain in the butt, tbh.. The rafters go up in a couple hours; we spent more time figuring out charlie stick height and placement, but all of the sheathing boards had to be cut in place, and as you get close to the top the angles are such that the boards don't lay flat at all. I also made a gazebo with a reciprocal roof--sheathed with poles and put cedar shakes on them. Also took me an insane amount of time... It's fun how the rafters go up quick, but there's gotta be a better way to sheath them.. [noidea'

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Offline Don_P

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Re: Round Cob Cottage w/ Sod Roof in MI w/ Video
« Reply #4 on: November 18, 2017, 02:44:47 PM »
That's what it's looked like. Hand in hand framing is fun, we've done Leonardo's bridge and also used the same reciprocal methods for shelter with the local kids. If you set the reciprocal rafters and then set "common" rafters directly above them straight up and down the roof from a crossing at the center directly down to the top of the closest reciprocal foot. Then it should plane in like a multi faceted hip rather than sawtoothing. Not sure how it would look inside though, busy.

Offline Ernest T. Bass

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Re: Round Cob Cottage w/ Sod Roof in MI w/ Video
« Reply #5 on: November 19, 2017, 03:18:47 PM »
Sounds interesting, but I'm not quite getting the picture?

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Offline Don_P

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Re: Round Cob Cottage w/ Sod Roof in MI w/ Video
« Reply #6 on: November 20, 2017, 04:38:14 AM »
That's not an easy picture to draw  d*

I've drawn 2 common rafters running straight down from the occulus to the plate ring, this removes the stepping but at quite a busy cost...  an alien yurt lands on a recip roof  :D

Offline azgreg

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Re: Round Cob Cottage w/ Sod Roof in MI w/ Video
« Reply #7 on: November 20, 2017, 06:00:25 AM »
Looks like a nightmare to me.


Offline Don_P

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Re: Round Cob Cottage w/ Sod Roof in MI w/ Video
« Reply #8 on: November 20, 2017, 11:55:37 AM »
More doodling on it. The reciprocal, self supporting, rafters in orange, the common rafters in gold. The commons run just like hip rafters.



It actually looks fine inside, at least on a screen, I think the commons would blend into the ceiling and the show is still the recip rafters.


Another type of reciprocal frame to google  Davinci's Bridge. Leonardo DaVinci was commissioned by the Medici's to devise a simple bridge that soldiers could easily and quickly build out of readily available materials. Again interlocking self supporting "hand in hand" framing
The Chinese had by that time been calling that a rainbow bridge for about 1,000 years  :D
« Last Edit: November 20, 2017, 02:53:29 PM by Don_P »

Offline Ernest T. Bass

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Re: Round Cob Cottage w/ Sod Roof in MI w/ Video
« Reply #9 on: November 20, 2017, 04:50:37 PM »
Pretty sweet drawings... It's the kind of thing that's hard to wrap your head around, but makes sense once you start to do it. Seems like the common rafter method could translate to logs, and it still looks cool.. I would definitely go that route if I was going to install metal roofing (or pretty much anything besides sod..).

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Offline Don_P

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Re: Round Cob Cottage w/ Sod Roof in MI w/ Video
« Reply #10 on: November 23, 2017, 07:29:20 PM »
I think it lends itself to log better than rectangular timber, sketchup is just easier drawing in rectangular.

The look is stunning.  What is earth plaster and how is it applied to the cordwood?  I guess what I'm wondering is what keeps an earth covered pile of wood from becoming a termite condo?

Offline Ernest T. Bass

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Re: Round Cob Cottage w/ Sod Roof in MI w/ Video
« Reply #11 on: November 24, 2017, 09:32:58 PM »
Well, for one we don't have termites here.. :) I don't know why it would be more susceptible to insect damage than regular cordwood, or any other log building (less perhaps, since every piece of wood is separated from its neighbors). Mary has had some odd ant invasions at points, but she's been able to keep them under control.

Since the cordwood mortar is rough earth to begin with, the earth plaster (clay, sand, some water-repelling and sticky-enhancing additives like flour glue) sticks great to the wetted wall. The cordwood is small enough in diameter that the plaster goes right over the log faces (with a little chopped straw in the first coat). She may finish with a white lime plaster eventually, but our raw cob plaster has been doing okay on the main house for years now.

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