Planting boxes being installed on our green roof

We spent the weekend building the planting boxes, getting about half of the garage roof covered. Each box is 24 to 30 inches wide, and up to 48" long. We're making them as close to a standard size as we can for our convenience, and then filling in any open space with pavers or river rock and gravel.

The box construction is from treated 1x4 pine, with the corners reinforced by small pieces of treated 2x2s. We're screwing the boards into the corner reinforcement with deck screws. For construction convenience, we are screwing the 2x2 pieces to the shorter 1x4 sides as a sub-assembly, and then making a jig from clamps and boards on a piece of plywood on sawhorses to put the sides (boards) and the sub-assemblies together. We tried to build the first couple of boxes on the driveway surface, but the driveway is not flat, and it increased the amount of bend-and-stoop we had to do. Elevating the worksurface --- and working on a flat stable surface --- made the boxes much more uniform, as well as making the task easier for our 50 year-old bodies.

Each screw goes into a pre-drilled hole to minimize splits, since we are screwing into two sides of the 2x2s. It took us a couple of hours to get a "system" worked out, but it is now going rather easily.

We lift the box to the roof surface, staple fiberglass screening to the bottom AND to the top, anchoring the top along one edge only. The box then goes into place.

The box is filled to about half-depth with perlite, and then filled the rest of the way with a commercial composted bark-based planting medium ( MetroMix 560).  We then pull the screening over the box, and staple down the remaining three sides. 

 

This week should see us getting the remainder of the boxes built and filled.  Planting will then begin.  Right now, we plan to use mostly sedums and sempervivums.  It is also very likely that we will do some trial plantings of small low-growing spring-flowering bulbs.  Our green roof installation is over an unheated garage, so the planting boxes will be exposed to cold temperatures both above and below.  I am expecting this to limit the species which will thrive under these conditions. 

 

There will be extensive planting posts as this project moves forward.  Species, varieties, sources, successes and failures.  And, of course, pictures.