Yesterday was our very first day loading soil onto our rooftop, the official start of building our living roof! We used a pulley system to raise 5 gal. buckets up to the roof, where a line of people passed buckets to be dumped. It was a whole lot of fun, and it’s great to see our green roof coming to fruition, after weeks of scheming. Here’s a little bit more about our process.
Just like building our cob house, the living roof of our new straw bale house has had me thinking for hours, and quite honestly, it’s been the source of a lot of anxiety throughout the entire construction process. Gobcobatron was a breeze in comparison — single story, low to the ground, not a huge roof area.
But how would we get soil 25 feet up into the air, at the highest point on our new building? What type of soil, and how would it stay in place? Would people feel safe scampering all over the roof if we did the work by hand? Just how many hours of work is this going to take, anyway?
Green Roofs: Soil Versus Sod
We decided to use loose topsoil on Strawtron, as it was already available in a large pile not far from the house. No sod squares this time, as we didn’t have an immediate source. Plus, we wanted to try seeding the soil intentionally this time to see if we could select grass species that we really want. The beauty of sod is that you have a contained “piece” of soil that can be picked up, moved around, and laid down, and there’s no waiting for grass to grow. It’s like a ready-made.
The trick of using loose soil is figuring our how to move it around, and what to do in the meantime before it is rooted and firmly in place on the rooftop.
Moving Soil onto the Roof
We used a tractor to move a large pile of soil close to the house, where people could shovel the dirt into buckets. Yesterday, I rigged up a pulley system lashed to scaffolding so that those buckets could be pulled up right to the edge of the roof, with little effort.
One person shoveled, one person pulled buckets up into the air, and a group of people passed the buckets up on the roof (without having to take too many steps), where the last person dumped the bucket. Simple enough, right? Well, it definitely worked pretty well, once we found our rhythm. Personally, I am not a terribly huge fan of heights, and do not relish walking all over the roof, but amazingly, people became very comfortable after a short period of time and were traversing all over the place.
This is a really tall roof, and perhaps the view made it all worthwhile.
The pulleys were critical, and having the soil so close was also very important, not to mention having enough hands to have a steady flow of work.
Containing the Living Roof
But… how does the soil stay up on the roof, since it’s loose? We devised a “soil ladder” system to contain and hold the soil on the roof while grasses take root. (I tried this system on Gobcobatron, but ditched it since it was ultimately unnecessary — the sod held itself fine.) Basically, we tied a series of 2x4s together with rope, with 3-4 feet of space between each stick, and laid the ladder over the ridge of the roof. The 2x4s (on edge) provide a stop for the soil from sliding down, and once soil is on both sides of the ridge, there should be even transfer of load on the assembly.
This is, of course, going to rot over time, but that is the beauty of it — once the soil is rooted, the ladder is unnecessary, and the 2x4s will compost. The rope…. well, I’ll just dig it up one day, or leave it. No biggie.
Green Roof Edge Restraint
The detail that has caused me the most concern the is the edge restraint — how to keep the soil from sliding off right at the very edge. I will write more about this in a future post, but it entails a white oak 2×4 elevated one inch off of the roof deck, metal flashing, and gravel for drainage. The gravel will line the perimeter of the roof up to the 2×4, which is raised up slightly to allow drainage off the roof, over metal flashing under the 2×4, and right off the edge into a gutter on a fascia.
We are saving this work until we had the weight of the soil holding down the EPDM pond liner completely.
More Soil to Come
In three hours, with 10-12 people, we covered 320 or so square feet of the rooftop with soil — not bad! I’d say the upper roof is at least 1/3 covered. With two more work parties we could probably finish the entire roof. It truly was a lot of fun, and I am extremely thankful for our great help in the process…. we never could have built a roof like this without a community of friends.