DIY Green Roof

DIY Green Roof - Intro

When building my Garden Office I opted for a DIY bio-diverse green roof. I read the guides , bought the seeds and then got to it.

DIY Green Roof - 1 Year in and already well established.

DIY Green Roof - Things I would do differently.

First off this is a guide of how I did it. I would advise the following changes.

1.  Thicker OSB or Plywood for roof 18mm minimum.
2. A thicker layer of growing medium minimum 2" or 50mm.
3.  Perhaps use sedum plants instead of seeds.

DIY Green Roof - The Roof Structure.

In order to support the weight of the green roof your roof structure will have to be fairly robust.

The DIY green roof on my garden office is supported by 4" x 2" (100mm x 50mm) timbers at 4 foot (60 cm) spacings. Board supporting the roof is 12mm OSB, which perhaps should be 18 mm. Opt for tanalised / treated timber where you can it is often not any more expensive and may well last longer. For a better quality build you may wish to substitute the OSB for Exterior Ply of a similar thickness.

To water proof on top of this goes 3 layers of visqueen damp proof membrane, one on top of the other. Obviously being careful with this is paramount, any holes and you will have leaks.

As above let the damp proof memebrane hang down over the edge by 8" or so, as we will dress over this with some wood next.

DIY Green Roof - The Roof Structure.

So at this point the garden office / shed should be  habitable and dry inside. The rest of the work is just for decoration, although it will add some protection to the water proof membrane.

After adding the decorative timbers the roof should look like this.

Here we can see the different types of timber used, and method of fixing (screws). Don't use to many screws as you want to keep holes in the damp proof membrane (DPM) on the vertical elements only. The above timber will give you a growing medium thickness of just 1". Which is only suitable for sedum, grass will not survive on this DIY green roof without constant watering.
  

DIY Green Roof - Prepare growing medium.

Sedum grows best in very well drained soils, and so compost is no good for a green roof. You will need a sandy  and gravelly mix. I used a mix of the following for my growing medium.

1. 4 Bags Pea Gravel
2. 4 Bag Limestone Ballast
3. 4 Bags Silver Sand
4. 2 Bag Compost 
5. 2 Bark Bark Chippings

The above will cover 8 meters squared to a depth of 25mm / 1".  And looks something like this. I would recommend doubling these quantities and having a 50 mm thick layer of growing medium.

DIY Green Roof - Sewing the sedum.

Planting the sedum is probably the trickiest bit, I avoided standing on the growing medium (protect that DPM), by sowing the seeds in strips perhaps 25% of the roof area at a time. If you were using small plants then you may wish to adopt the same principal.

 

The main thing to remember is not to puncture the membrane on the roof. Tip a bucket full of the green roof growing medium on the roof and then carefully spread around using a piece of wood, then use a piece of wood long enough as a screed. To level off the growing medium.

Sedum seeds are very very very small, and so you should mix them with dry sand to aid sowing, mix 400 or so seeds with 1 or 2 eggs cup full of sand and then sprinkle them on the the green roof, use your bit of wood to squiggle about the top layer of the growing medium to cover them over slightly, only VERY slightly, you are just trying to bed the seeds in to the surface. Not dig them in.

The sedum seeds will need to be watered until they are established, they germinate after about 2 weeks, and until they start to look fairly well developed you should continue watering. The thicker your growing medium the longer you can leave between watering.

DIY Green Roof - Did it work.

After sowing my seeds at the time of publishing in July, we then proceeded to have a very long dry spell, which I thought had done for my seed, as they had got wet for a week or two prior to the dry spell. BUT behold! I was applying some wood stain and noticed sprouts. . .

At present these little sdums which were sown from seed direct to the 1" thivk growing medium are around 10 - 15mm high. Will they survive the frost yet, I do not know.

Update: July 2014

It is now roughly 1 year since I planted this green roof with sedum, things are going well. We have had some prolonged dry spells and the roof has not suffered, the plants are flowering so it has been a success.

Update: 26/09/2016

Sunlight and Daylight Assessment

Visual Impact Assessment for Wind Turbine