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Seeking ideas for a roof on an octagonal, roundwood framed building with a fairly low slope...  RSS feed

 
Brian Rader
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Hi All,
I am hoping to cull the collective knowledge base here for some ideas on roofing an octagonal, roundwood-framed barn/out-building. The building uses a beefy (~18") cedar trunk as a centerpole. The roof pitch came out to be about 2.8 in 12. We had planned on a 3+ in 12 pitch but circumstances conspired against us & we ended up with a bit shallower pitch, limiting our options somewhat.

Really don't want to use asphalt shingles (from a financial & aesthetic perspective). Thought about metal (actually have some around that might work), but was STRONGLY caution against this by a builder we trust (said wind blown rain will keep the hip rafters wet & rot them). Thought about the velacreations latex concrete roof (even bought the Knott/Nez book: 'Latex Concrete Habitat'). When I calculated the amount of latex & the cost, however, decided to look for other alternatives. Latex is expensive & there is very little info about this approach online. Thought about cedar shingles. We live on an island in the PNW & there is a lot of cedar available. However, most resources suggest a pitch of at least 3 in 12.

This leads me to looking at a living roof or a simpler (?), lighter weight (?) moss roof. This is not an engineered structure. This has been and will continue to be true design-build (and not all of it that well thought out at times as I am learning as I go). I have no idea what kinds of loads my round wood framing can take. Plan would be to sheet the roof using boards or plywood, add EPDM (or similar, ideas encouraged), add media & some kind of drainage, then add moss/sedums/other. We are looking for simple, inexpensive, using as little purchased/manufactured product as possible. We are very puzzled by drainage issues & media/substrate. Any thoughts & ideas are appreciated. Right now all we have is the framed structure (tarped for the winter to minimize damage). We are open to possibilities & constantly limited by imagination! I will try to attach some pictures... I hope this works! Note for the pictures: each of the 8 pie shapes in the roof consist of 2 hip rafters (these go directly over the 8 outer posts to the cedar centerpost), 1 mid-rafter (these go from the centerpost to the mid-point of the beam (half way between each outer post)), and 2 jack-rafters (these attach to each of the hip rafters and span the distance between the hip rafter and the mid-rafter). With the addition of the jack rafters (not shown in the pix), the maximum distance between rafters is a bit over 2-feet at the bottom of the slope.

Here are some pictures. Thanks in advance for any ideas!!!
(tried to post 3 pix, but no luck. Trying again with one...)
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Brian Rader
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One picture worked, where three did not. Here is a second picture!
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Brian Rader
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3rd picture. This one shows the cedar centerpole where the hip and mid rafters are attached.
2014-09-01-(3).JPG
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Jay C. White Cloud
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Hi Brian,

Welcome to Permies...

I agree with not using the asphalt for not only aesthetics, but even more so for the nasty industry it comes from and the environmental impact in general of this product, when many other more appropriate and sustainable alternatives are available.

I can't say I follow your builder's advice about metal roofs are quite accurate, assuming the metal roof chosen is appropriate for the style and pitch of roof. It goes without saying also that any metal roof must be done well, and detail appropriately. If all these factors are perform well, then metal roofs are one of the most enduring (well over 100 years) and environmentally sustainable/recyclable. I will state from experience that on round hipped roofs, it takes a master roofer (and/or great attention to detail plus patients) to pull of a multi faceted metal roof, and if that is your builders point...he is more than correct...As when not done properly the hips are what "rot" first and often can happen unnoticed.

I know of and about "latex concrete roofs"...I have little positive to say of them from a "natural or permaculture" perspective, as they are supporting industries, modalities of architecture and concepts that are neither sustainable or historically proven to have endurance over time compared to other methods. I think they can be beautiful aesthetically, and offer perhaps a "creative venue" for some, yet are not either natural or a type of roof I would ever facilitate for a client.

Living roofs, to work well, really need to be designed from from before the architecture ever leaves paper and the drawing board. As an "afterthought" they can often (and are anyway) problematic. Either the structure is a true "fossorial building" with many cm (inches) of material on top or a specific design for the weight of this style roof. It should also be pointed out that this will require a "rubber" or similar material placed on them...A big can of worms in the long run...that I have been watching for over 40 years with EPDM and other membranes failing and/or needing repair. Most folks do not realized that this and tar roofs are not by any means,...new...They are all over the place, and most flat roofs in cities, box stores and the related have them. Its "big business" and "big industry." Now all folks are doing is adding plant material to the structure and calling them "living roofs." The living part is nice, but the 20 to 30 year life span? Not so much... I think some are getting better, and I know that the traditional (stone and/or built up layers of clay, earth, wood, sod, etc.) living roofs I have witnessed are great...they are not easy to facilitate...nor are they executed as an "after thought."

If you go with a "living roof" it really should be PE approved first for weight capacity!

If this was a project I had to assist a client with, I believe that a double roof system (which I design into many frames anyway) would be in order. This would give a potential for a insulative void being created, and the ability for changing the pitch to a much steeper angle.

If you have slate, or other appropriate flat stone, that is an option as well once you know the "live and dead weight" load capacities for this roof.

For "fast and cheap" (but may need replacement in less than 20 years) look for recycle rubber sheet material, and place it in "shingle fashion. I would recommend at least 2 (4 better) layers on a built up paper-felt carpet padding, over board or slab wood sheathing. Again watch the weight and understand it. Then perhaps some sod...maybe?

Good luck!

j
 
Jack Edmondson
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Location: Central Texas zone 8a, 800 chill hours 28 blessed inches of rain
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Brian,

I claim no expertise on natural roofs, but wanted to share a resource I think might be helpful if you go that route. I think a moss roof is the right way to go. Without engineering specs or species info on your log rafters, the less weight involved the less you stretch the envelope. Working with the aquaponic folks you realize that plants don't really need soil to grow. Dirt is heavy. The moss will give you the right medium. I have seen it done a lot in Alaska. A waterproof underlayment will also give you a wider margin of comfort. The link is for recycled vinyl billboard signage. At .12 cents a sq. ft. it is hard to beat for heavy mil waterproof material.

http://billboardtarps.com/product-category/billboard-vinyl/billboard-vinyl-13-16-oz/

Having battled moss on Western Washington shingle roofs for a number of years, I would also suggest doing someone a 'service' by removing their moss patches without copper compounds. One might find hundred of small colonies of moss patches already established that one could transplant into the hay bed to speed coverage. It might jump start your roof.
 
Alder Burns
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On two different sites I lived at in GA, I built two cabins largely sheathed in cardboard and carpet! This might be a cheap/free solution for you. On the roof, first I laid down a layer of cardboard, double thick if need be, such that one can walk on it. (My frame underneath, of bamboo or pine poles, was no more than 12-18 inches apart). Then tack up plastic, in overlapping courses. The roof should now shed water. Then I laid up old carpets, also in overlapping courses, with another layer of plastic under each one. The upper edge was nailed or stapled into the frame (the plastic under-layer of the course above it prevents a leak where the nail punches through). The "indoor-outdoor" carpet with a short, looped nap is easiest to handle and takes less stucco than shaggier types. Then, the whole was stuccoed with a watery mix of portland cement. The cement mix embeds into the carpet fibers and hardens into a solid sheet. (If the carpet scraps are new, let them age in the weather for a while before stuccoing as it often has a water-resistant treatment) At the one community I lived at, this cabin was the only building that did not leak in ten years, and I once had five people on that roof at once. All of the materials except the cement came from the kindly dumpsters; and eventually moss began to grow of itself on it. In a climate where moss grows more quickly, I wonder if the cement could be omitted, since the main purpose of it was to protect the carpet from breaking down in the sun. Carpet, cardboard, and plastic are waste materials benefitting from re-uses, often free for the hauling, and easy to handle.
 
Brian Rader
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Thanks you guys for the thoughts & ideas. I appreciate you taking the time to reply!

Jay: Thanks for the big welcome (long time reader, first time poster)! I think you got the essence of the roofer's comment... very, very difficult to make 8 seams watertight with metal on this kind of structure. He described a previous experience with a similar structure as one of the more difficult & frustrating building projects he had taken on. And, I am no professional! Thanks also for your thoughts on latex & "living" roofs. It is unlikely that I will get a PE to do load calcs. Going to have to try & keep it as light as possible to stay on the safe side. Actually, we had been reading about Jack's moss idea & are intrigued by that...

Jack: Thanks for the moss idea & vinyl link. I need to do some more research on this. Interested in the lighter weight of of moss roof, but still get the "living" look. Need to understand if vinyl would hold up. Need to figure out if some kind of substrate ("soil") would still be needed. Need to understand if root barrier and/or drainage is needed. I have a nice healthy crop of moss growing in my yard right now! I read somewhere that you can put moss in a blender with yogurt & then paint it on! Need to learn more before spring!

Alder: I like the cardboard/carpet/cement idea, too! Kind of takes me back to latex-concrete, w/o the latex (& maybe w/o the concrete!). Like in my reply to Jack, could be that a fairly lightweight carpet might be a good substrate for the moss. Great ideas!

I am also thinking that this building needs some kind of cupula! Would like to show off the wagon wheel around the center pole & let some light in. May also try to incorporate some ventilation. Building is likely going to be a combination barn & chicken coop, but you never know!

Thanks again ! ! !

Brian.
 
Jay C. White Cloud
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Hey Brian, et al,

...very, very difficult to make 8 seams watertight with metal on this kind of structure...


SO TRUE!! Unless (and even then it is a pain in our "behinds') you are a master metal roofer...this is a real challenging type of roof...No matter what style metal, ie. copper shingle, lead, standing seam, or wire down corrugated...They are all difficulty on multi hipped and/or round roofs...

I (have) design moss gardens and related landscapes. There are a number of methods that work and some can be applicable to a lighter weight living roof. I don't do concrete, plastic, etc unless recycled material and/or the project spec's before my involvement was engineered for them.

Now one possible method is a mix of "old and new." The pitch is a "wee-bit" low, which concerns me, yet I think you can pull it off. The roof will tell you if its getting over loaded when you walk on it. It will begin to sag more in the spans and the "bounce" will become lethargic...That is an "old" empirical way models where checked for stone and tile roofs.

1. I would cover the inside that you see with a light bamboo or other reed matting, or a "woven matting" that can be made with scrap material cut on a table saw like I will share below. You can also use fern fronds to form a matting that is rather pleasing as well... Below are some different examples and possibilities to think about.


400 year old Minka farm house attic displaying traditional reed matting...


Contemporary version of the above in a Minka project in Vermont...


One of my students projects for an Asian-Craftsman style timber frame in New York State...



These are the panels made from scrap that is ripped on a table saw to approximately 30 to 40 mm wide by about 3 mm thick. They look nice and are very easy to make...

2. Once you have the ceiling you will be looking at sorted out, even if its just fabric of some type, you will need your first layer of waterproofing...

I would suggest a minimum of a five ply layer (10 layers is much better and you could go all the way to 50 in you project) of newspaper and brown or red building paper. I start with the building paper then newspaper. This is "wetted" with a sizing or glue water (many paper mache formulas will work as well as others...ask if you have questions.)

Once this is down it is going to get oil with flax oil at a minimum, yet I would use a mix of pine rosin, tung, flax, and citrus oil mixed with beeswax.

3. Now you can start getting into the "workhorse" of what is going to keep the building dry. It can be "shingling" of recycled vinyl, plastic, 5 lb tin cans cut open and flattened, tar paper, etc.

This does not simple go down onto the "paper layer", but should be attached to a grid of 20mm think x 30mm strapping that runs with the direction of the rafters and covered with "ribs" of similar strapping to support your water proofing material. This creates a "rain screen" or "cold roof" effect that allows moisture from inside to not condense against the paper but rather move into a dry venting space.

4. With the above complete, my first choice is "felt carpet padding" that is recycled from local carpet companies...they love not having to take this to the dump. This material is laid like shingle, and can even be oiled itself unless you want a living roof, then it is going to get treated with ground up moss, sour old milk, goat or rabbit droppings, and urine if you can get it (about 1 gallon per 100 square feet for the urine) This mix smells a bit but also provides the starter for your living roof. If you go this route I will give you a specific ration latter.

Now your moss of choice and/or sedum mix is planted (or sewn) onto this matrix. It will be spotting at first yet in time will start to "culture" itself to the environment. I have seen "stone fern" and other plants also used.

The caveat is the durability of the actual recycled "waterproofing" layer and how long it will last. In general you should get 20 years minimum.

I do like the idea of a cupola with a steeper pitch and perhaps wood shingle. I would also not instead of the recycled material for the body of your roof, you could go with a shake or sawn wood shingle roof as well just understanding that it will not last long at that pitch.

Regards,

j
 
Brian Rader
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Thanks again for all the help & responses to this.  Making progress & thought I should share some pictures.  First, cupola & moss roof... view from the ground!
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Brian Rader
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Next, a close up of the moss roof & the cupola!
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Brian Rader
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Cedar shake siding & rescued craftsman windows.
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Brian Rader
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Closeup of siding & windows. 
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