Hello folks.

My question is about the roof of a cabin I recently bought in Northern Spain, in a protected area. I need to rebuild the roof (it’s about to collapse) which is tiled by very heavy flagstones.
 
At the beginning my idea was to rebuild the roof decking and place the stones back on top. For that purpose I needed some way to “glue” the stones to the decking, which is impossible unless I lay a layer of concrete underneath so the stones can be mortared to it.

The problem (and I discovered it afterwards) is that there is no way to find anybody who would install the stones. It is a very specialised job, and all the suitable builders want the whole project and would not accept to place the stones unless they have built the whole structure.

Then, after a trip to Norway, another idea started forming in my mind: A sod roof.

There is nothing more beautiful than a green roof. And nothing that insulates more. The problem for a peniless guy like me comes with the money. The costs of an “engineered” green roof are even higher than using the stones. All the new fancy systems are composed of a huge number of layers of expensive materials.

In Norway somebody told me that all they use is a metallic corrugated on the roof deck, and then some soil and then the turf. Don’t you think it sounds too simple to be true? Being a pitched roof, I can see how the soil may slide down the roof, even when there are retentive frames.

I saw what the “modern” Norwegians were using, which is way simpler, and it seems like it works: http://www.isola.com/com/apps/isolareddll/showprod5ab0.html , where the membrane (laid directly on the waterproof felt) is the root barrier if properly applied. I could also find a UK made membrane http://www.safeguardeurope.com.

But then I found a Swiss manufacturer http://www.eternit.ch/uploads/media/Doku_GREEN_01.pdf that implements another simple approach, by superposing two layers of ondulated fibrocement sheets, where the lower one drains away the water and the top one keeps the soil in place for pitches up to 45 degres. No further root barriers, filters or waterproof membranes are needed.

Have any of you ever built a green roof? Which of these solution would be the most cost-effective and most importantly DURABLE?
Any idea about the way to calculate the structural needs providing the total weight of the roof when the soil is saturated and one metre of snow is laying on top?

There are loads of documents talking about green roofs, but nowhere to say how to actually build one… Thank you guys, I hope you find this topic as interesting as I do!
Miguel.