Green roof construction

This is the first post documenting the evolution in the construction of our cottage for wood. The house is topped with a green roof and its structure is made out of freshly cut young acacia and some recycled boards we found in the barn.


This is a rough model depicting the construction of the structure. It is basically four (only three in the model) frames, leaning on a concrete wall about 1m high in one line of columns and the other in a foundation on the ground. Beams are 2,5 x 17 cm boards every 120 cm. The span of each beam is 4 meters. Below is the final result of the structure.

Starting the construction


Structure is done

Another interesting feature that needed to be done for this little cottage is the floor: it is made out of gravel, stone and cement. In the first place, the covering 10 cm of grass and earth had to be removed. Unfortunately, we didn’t think of it beforehand, so we just removed the layer of grass and roots and piled it away, instead of carefully locating it somewhere else for later use in the green roof. This gave us extra work eventually as 20 m² of the same layer had to be taken from 15 meters away…

The underlying earth was rammed manually with a big wooden trunk in order to have a flat working surface. Also some levelling was in order although for this kind of construction is not essential. The movement of earth gave place to some draining work, as the wall above contains a lot of water. A pipe was passed underneath taking advantage of the existing draining of the plot.

On top of the rammed earth a layer of gravel was displayed, over which big flat stones (about 40 x 40 pieces) taken from nearby were put and levelled. The surface was divided with old recycled bricks to make the work easier. The gaps were filled with more gravel and adhered with cement.



The water collecting system from the green roof was tested and worked perfectly from the first rain. There is an inclination of 5% so it is enough for water to gain speed but not so much to erode our green roof. An initial set of boards was displayed inside to start putting the wood as soon as possible.


The most delicate part of the design is in the edge where water will be evacuated, so we chose to recycle some old clay tiles. The water insulation was put on top of the tiles with the purpose of protecting the underlying board from moist. This will also create a pond as a reservoir of water along the lower line of the roof that will serve to more thirsty plants.


All the perimeter of the roof has a line of gravel to hold down the tar sheet, and to serve as draining system.



Almost finished

The natural plants from the terrain were put plus some species of characteristic resistance, as there is no intention of watering the green roof with other than rain…



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