The Year of Mud: Building a cob house » Living Sod Roof

Strawberries on a living sod roof

ziggy — Sun, 07 Jun 2009 02:19:46 +0000

Here it is…. the first food from the sod roof of my cob house. Mm mm.

Building a living sod roof for a cob house

ziggy — Fri, 15 May 2009 02:15:52 +0000

At long last, I have a living roof! I’ve been anticipating this day for over a year now and it’s finally done. On Monday, a group of about twelve folks assembled to help me lift sod onto the top of my roof, and in two and a half hours, it was effectively covered.

Soil retaining ladders

A few days prior to Monday, I made several soil “retaining ladders” using rope and some thin wood poles to help keep the soil in place. These poles were spaced a couple of feet apart to provide a brake for the soil from sliding down the roof. At some point I ditched the idea of using any loose soil on the roof in favor of entirely using sod, so these ladders became less important to me, but I left them up anyway.

Building the sod roof

Since I already wrote about cutting sod for my roof, I will descrive how the sod was loaded. Once the perimeter of the roof was covered with sod, we covered the rest of the roof. Doing the edge was the trickiest part, since I had the fold the EPDM underneath itself and leave a little bit exposed to protect the edge logs.

Once that was done, it was only a matter of lifting the material onto the roof. People worked at ground level to pass the turf up to folks on scaffolding and ladders, who then passed the material to others on the roof. The turf squares were packed closely together so that there were no gaps. If any awkward gaps could not be filled with sod squares, loose soil was loaded into cracks.

It was all fairly simple. Heavy heavy, but simple. I still have to load some sod up at the very top of the roof to completely cover the tractor tire skylight frame, but the roof is effectively done.

Planting the living roof

On the east side of the roof, I dumped several buckets of loose soil so that I could put in several strawberry plants. I mulched the strawberries with straw to help conserve moisture.

Eventually, I will plant wildflowers, grasses, and edible perennials on the roof, focusing on plants that are tolerant of drier soils and full sun. Since the sod is only about four inches thick, it is likely that the roof will dry out during high summer.

Although… yesterday was an incredible first test of the integrity of my living roof. At 6:30 p.m., we were warned of a tornado headed straight for Rutledge. Within 30 minutes, an inch and a half of rain had fallen, but thankfully the tornado turned at what felt like the last minute, and we were spared. It missed us by a mere 10 miles. I was happy to find that the soil remained intact on the roof, and none of the sod slipped. I didn’t see any signs of wear on the rafters, either. Success!

It will be interesting to see how the living roof ecology develops and changes over time. It will be especially nice once the individual sods root together and get totally established.

My living reciprocal roof formula

Here is my living reciprocal roof formula, in layers:

28 round pole rafters (black locust and pin oak, 14 primary, 14 secondary)
black walnut wood decking (mostly 1-1.5x)
muslin fabric
double layer of cardboard
EPDM
four inch thick sod squares

And finally… a few more photos from the sod roof party:

Starting to build the living roof

ziggy — Fri, 08 May 2009 14:11:55 +0000

Lately I have been focusing a lot of my attention on building the living roof (a.k.a. green roof, sod roof, or turf roof). Last week, I finished building an edge board – a sort of retaining wall around the perimeter of the roof to help hold the soil from sliding off the roof. I debated quite a bit about how to construct the edge board, and eventually I decided that I would use round black locust logs spiked into the rafter ends with giant 8″ nails. Unfortunately, the logs only extend a couple of inches above the height of the roof, so it’s less of a retaining “wall” and more of a little edge “bump.” (See above photo for a better idea.) I’m not too afraid of soil sliding off the roof, so I’m not that worried.

Cutting sod squares

Originally, my plan was to use loose soil on most of the roof. I thought I’d use loose soil because we are having some road work done in the near future, and much of the topsoil will be scraped and made available. Instead, I am using sod squares. Ma’ikwe, another Dancing Rabbit member is building a new home this year, and she very kindly gave me permission to cut sod from the footprint of her future home. Sod is much more ideal than loose soil because it already has grasses and root structure established.

I’ve gotten into a pretty good groove cutting the sod using a simple flat trench shovel. Each square is something like 4-6″ thick and very heavy. I’ve moved dozens of wheelbarrows full of this sod to my building site.

Loading the sod

Recently, I put a few of these sod pieces (or “turves”) up on the edge of the roof. I decided to fold the EPDM under itself at the roof edge and slightly up over the log edge board. It looks a little less than ideal, but then again, the soil will eventually settle and perhaps cover the EPDM from sight. I’m not sure. It’s kind of an experiment. I want the EPDM to protect the logs, but I don’t want it to come all the way around the edge. I’m also want to have the option of adding a gutter to the edge in the future.

Next week, I’m planning to have a work party to completely cover the roof in soil. This is a huge step!

Getting in the last building work before winter

ziggy — Mon, 03 Nov 2008 04:18:28 +0000

I will be headed out of Dancing Rabbit in three short weeks to go back to New Jersey for the holidays. Within the past couple of weeks, I have accepted the fact that I will not absolutely “finish” the house before that time. By “finish”, I mean complete the roof, finish the floor, make my rocket stove and cob bed and bench, and plaster the interior.

So. I’ve done some prioritizing. Now that the cob walls are complete, and the windows and door are in, the house is sealed. My biggest remaining priority is the roof – I need to construct an edge board around the roof, create a soil-retaining system, and have soil moved to my site and load it onto the roof. Oh, and seed the soil, too. That’s not a small load of work by any means!

While I am waiting on a delivery of lumber to build my edge board, I have begun (and finished) some scratch plastering. A few days ago, I moved several tons of gravel into the building in preparation for the earthen floor, and raked it level and tamped it with Kyle’s help. (I estimate it was about six tons, all of which was moved within a 24 hour period.)

The chances are pretty decent that I will be able to finish the floor and the roof. If I do these two things, I will feel confident about moving in for the winter. I am pretty opposed to moving into an unfinished house – especially one without a floor. It would be quite a hassle to work on the house when springtime came (and springtime rains) with all of my stuff in the house and nowhere to store it. However, if at least the floor is done, it won’t be quite as difficult to work on the stove and cob bed and plaster with things in the space.

The weather has been phenomenal lately, which has definitely contributed to quick progress on things. There’s at least a few more days of warm weather in the forecast, too, which is promising.

Three weeks to go! Let’s see what can get done.

Cob walls complete, windows and door installed, and more!

ziggy — Thu, 30 Oct 2008 23:27:50 +0000

The past week or so has been quite eventful. There’s been mostly positive progress, but some negative, too.

Cobbing complete!

With Karen’s and my dad’s help, I completed cobbing. The walls are finally done! In just a few days, the gap between the walls and the roof was closed. It was very satisfying to see the final line of the wall meet the decking of the roof. It was awkward work having to stuff the small spaces, but it wasn’t too bad…

Windows and door installation

Next came the windows and the door. My dad and I struggled with installing the first of three windows, continuing our typically discombobulated history of collaborating on work projects. After a couple of hours, we got it in, and the next two were much easier. The north and west windows are casement style, and the southeast is double hung. All are doubled paned.

The door was surprisingly easy to install. A few shims here and there and it was set. Unfortunately, however, it’s not quite what I expected. Meaning that I must have looked at the door wrong when I first found it, and it doesn’t actually open the way I expected it would. It opens outwards instead of inwards. For now, I’m not locking it in cob, just in case I decide to change the door later (or even make my own door). It keeps the cold out, which is good enough for now.

I used sheep’s wool to insulate around the window and door frames where there are air gaps. The wool was free from a local farm, and I simply carded it using my hands before stuffing it in the gaps. The house is now sealed!

Losing my EPDM membrane…. almost

Beyond all that… the biggest happening of the week was almost losing my EPDM membrane on a very windy day this most recent weekend. What a nightmare. All day Sunday, there were gusts of wind up to 45 mph. Since the pond liner was not tied down or weighted in any significant way, it was flapping pretty heavily throughout the day. At one point, my dad ran to find me and said “your roof is about to blow away”, and we made it out there just after the ropes around the tractor tire flew off, essentially freeing the membrane from the roof completely.

We held onto the corners for dear life, and then Jeff ran to find help. Soon a pack of ten or more people were running towards the house, and each grabbed a corner of the membrane, some getting smacked in the face by the EPDM in the wicked wind. Tony and I scaled the house carrying rope, and working like spiders, we all wove a giant web over the membrane. It was a pretty intense experience. People were being lifted off the ground as they held onto the membrane, and up on the roof it was no better. Every time there was a giant gust, the membrane lifted us up off the surface, and there was little to hold onto. Frightening.

Eventually we got the whole roof tied down. Unfortunately, I think the membrane suffered a bit in the process, and there is some damage and wear. Hopefully the parts that are damaged are close enough to the edge that will get trimmed. I also lost some cardboard cushioning that will have to be replaced, so it’s going to take a fair amount of work to get that material back under the EPDM and prepare for the next step in constructing the roof.

Scratch plastering

In the meantime, I’ve been doing some scratch plaster inside the house with the help of my new (and probably last) work exchanger, Kyle. We smoothed out the nooks and shelves, and some of the rougher parts of the wall that experienced some rain damage. It’s amazing how much more pleasing/smooth it looks now, even before the final coat of plaster is on.

Prepping for the earthen floor

Today, Kyle and I cleaned out the house and raked up loose cob and some grass to prepare for moving gravel inside. I decided to leave the topsoil in my building. I didn’t level it either, figuring that if any moisture did get in there, it would drain more easily with the natural slope. The soil has been well tamped by now, after walking on the ground all season, and mixing cob in there as well.

We moved gravel in by wheelbarrow. Because of the slope of the site, the gravel will be 4″ deep on the east, and up to 12″ deep on the west. Above this gravel will be 5″ total inches of earthen floor mix (divided between two layers).

I expect we’ll finish the gravel moving tomorrow, just in time for our traveling Halloween party. I plan on having a gravel-tamping dance party during at my stop. Many feet make work light!

Pictures coming soon!

Dressing up the reciprocal roof

ziggy — Mon, 20 Oct 2008 00:32:12 +0000

Before the EPDM went on the roof, I wanted to add a cushion of cardboard on top of the rafters and decking to protect the membrane. And before the cardboard went on, I wanted to add some kind of fabric so that the cardboard would not be visible from inside of the space. I bought a 50 yard bolt of muslin for $50 at Zimmerman’s, and Karen (my current work exchanger) and I draped the fabric and stapled it to the decking.

Next went the cardboard. This was pretty tricky since the cardboard was so slippery and could not be easily traversed while affixing it to the decking. I used some short nails to try to help it stay in place, which I wasn’t totally thrilled about having to do, since I wanted to minimize pointy things immediately underneath the EPDM. But it wouldn’t really stay in place otherwise.

With the addition of the tractor tire and cardboard, the house was looking rather…. interesting…

Next came the impermeable membrane: the 35′x35′ sheet of EPDM, weighing in at 380 pounds. With the help of at least a dozen or more other people, we unraveled the EPDM from its roll, and hoisted it up on the middle of the roof. From there, we unfolded it and spread it across the surface of the roof.

Without that many hands, the lifting of the membrane would have been an incredible chore…. perhaps even impossible…

I am incredibly relieved to now have the EPDM sitting on the roof. This means I will never again have to get out of bed at 3:00 AM to check to see if the tarps are still covering the roof during a thunderstorm.

Next up: trimming the membrane, making eaves and finishing the skylight, and then lifting lots and lots of soil for the living roof…

EPDM pond liner for living roof construction

ziggy — Tue, 07 Oct 2008 22:11:59 +0000

Last week, I ordered the most expensive material for my entire cob house: the EPDM pond liner for my (soon-coming) living roof. EPDM is a synthetic, petroleum-based rubber product commonly used for living roofs, due to its strength and durability. Apparently, it can last 50 years exposed to the sun, and presumably longer buried under dirt.

I have not been thrilled by the prospect of purchasing this petro product for my house (it’s one of the few new, synthetic materials in the whole building); however, it has been challenging to find information on building a living roof using natural materials. Apparently, Norwegians have historically used birch bark as their impermeable membrane. Getting more information than just that has proved difficult, and still, I probably wouldn’t have been willing to experiment with my first house, considering just how important a good roof is. I want to do this right. Perhaps I’ll experiment with an all-natural living roof on a different building in the future. (If anyone out there has details on any books, etc. with information on traditional living roofs, let me know!)

Anyway, the 35′x35′ sheet of EPDM cost a whopping $622, at least $100 of which was the shipping cost. The thing weighs 380 pounds. I’m pretty daunted by the idea of somehow getting this whole thing unrolled over the roof… but I’m sure with enough hands, it won’t be so bad!

Preparing for building the reciprocal roof frame

ziggy — Tue, 12 Aug 2008 02:32:10 +0000

The past few days, I have been dwelling quite heavily on the roof design for my cob house. I will be constructing what is called a reciprocal roof, a self-supporting structure composed of pin oak and black locust poles. Reciprocal roofs are round and spiral-y, perfect for round structures. They require no center post and are apparently “simple” to construct, requiring no experience. Plus, they look great, too.

The only downside to building a reciprocal roof is the apparent lack of really comprehensive information out there on how to actually do it. Running a Google search for reciprocal roofs results in a few decent hits, but still, there seems to be a dearth of hard information on how to go about making a reciprocal roof from start to finish.

The best resource I have found thus far is Tony Wrench’s book, How To Build a Low-Impact Roundhouse. You can see some photos of his design here. Wrench has some good sketches and a decent amount of how-to information in his book (which, by the way, is pretty hard to find), but I’m still craving more. Perhaps because my case is pretty different from his and I want to be reassured that this thing is going to work.

The main difference being that my walls are load-bearing, with the reciprocal roof rafters resting directly on the cob walls. Oh, and my house is also not totally circular… That makes a big difference, too.

But anyway, here are a few other sources of images and information for the prospective reciprocal roofer:

The LessPress Snail Cabin has a reciprocal roof made with dimensional lumber. Also, be sure to check out their Excel spreadsheet for calculating beam lengths and positions for both circular buildings and otherwise
Zone5 has a brief description with some images of a Tony Wrench-style reciprocal roof construction for a roundhouse here and here
Check out a scale reciprocal roof model and design using dimensional lumber at Casa de Baro
Cae Mabon in Snowdonia of North Wales features several buildings with reciprocal roofs. Images here
Simon Dale’s ‘low impact woodland home‘ has a gorgeous reciprocal roof with gnarly rafters and beautiful slab decking
For math nerds, visit The Pavilion for a very technical description of how reciprocal roofs function
Design Forward has a very brief snippet about the history of the reciprocal roof design, which was invented by Graham Brown, who says: “The structure demonstrates a principle that is fundamental to life on this planet – a simple natural principle: All life is connected.” (Unfortunately, Brown’s website is down…)

This is mostly what I have been reading and looking at for inspiration. I guess the only way to determine if my own reciprocal roof design works is actually making this thing. Soon enough, I will know!

(Image from Zone5.org)

Peeling bark

ziggy — Sun, 30 Mar 2008 16:18:08 +0000

The past couple of days, I began peeling bark off of the logs for the rafters of my living roof. I’m using a borrowed drawknife, a long, curved, two-handled blade for peeling back the bark. It’s sorta like whittling, only on a bigger scale. The idea is to peel back both the bark and cambium, which is just below the bark. That leaves only the smooth wood remaining. It’s pretty exciting to imagine these logs in the final building some day.

Lumberjacking

ziggy — Thu, 20 Mar 2008 21:29:47 +0000

The days have been packed recently. A few days ago, I began cutting down pin oak trees for the living roof of my cob house. On Tuesday morning, Dan lent me a hand and we took down three trees in an hour and a half, despite the ground being quite muddy.

This morning, I went out alone and cut down a tricky tree more centrally located in a dense patch of pin oaks. It was very tough to bring down, since it was hung up in the tops of the trees. I walked back to the village, and thankfully Liat offered some help, and together we shook and pulled and dragged the tree down. This afternoon, I cut a smaller tree and easily toppled it. That leaves me with five total trees thus far. Hopefully I will be able to get at least two rafter poles from each. I need between twelve and sixteen of them.

The patch of land that I have been doing the cutting is very dense with pin oaks. Some are growing mere inches from one another. Pin oaks are tall and straight, making them appropriate for the reciprocal roof I want to build. The toughest part of the job is not so much the cutting, but the toppling of the trees, since they are so tangled with their neighbor trees. All of the cutting has been done with a bow saw, a hatchet, and a smaller saw for branches. It has been gratifying work.

Unfortunately, I don’t yet have a plot of land for my house. I have been in talks with another member here who is interested in letting go of his warren, since he has determined that it’s not worth the cost to him for the small amount of gardening he does on it. So there is that possibility. Because it’s not definite, I have not bothered with transporting the trees back to the village. (A damp ground doesn’t really help with that, either, though, which is probably the real reason I haven’t carted them back.)

We shall see.