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

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How to Build a Garden Office

How to Build a Garden Office - Intro

In this post I aim to describe how you build a fairly shabby, but well insulated garden office for under £1000.

Before you start draw a plan of you office on a bit of paper, and work out how much wood you will need and make sure you have enough space for everything you intend to put in the office. See my garden office plan.

Specs:

• OSB and Plywood Cladding
• 4" x 2" (100 x 50) framing
• Knauf acoustic role insulation 100mm.
• Reclaimed upvc double glazing units.
• Damp proof floor
• Sedum roof.

How to Build a Garden Office - Choosing Your materials

Wood

Perhaps the most important consideration is cost, a green roof is cheap and 10mm shuttering ply board is also cheap which is why I have opted for them. where you buy your timber can make a big difference. All my timber came from Travis Perkins, which came out cheapest when I quoted around.

Other more attractive external and internal cladding materials might be considered such as ship lap, or taper cut or external tongue and groove.

A garden office built with ship lap timber.

shuttering ply - not as pretty!

Despite not being very pretty ply wood as an exterior office cladding has two main advantages:

1. Increased weather proofness- unlike building with ship lap you will not end up with loads of little cracks which wind and rain can get in to the garden office.
2. Quicker - 1 bit of ply board will cover 2.88 m sq. so you will be working a lot quicker than you would with ship lap or taper cut.

Insulation

If you intend to work in your office over winter you will need to insulate it, unless you want to run up a large heating bill. 100mm of insulation is good, rolled mineral wool if you are on a budget, if you can afford some rigid foam board or XPS then lucky you. Don't forget insulation can keep you cool in summer too, and keep out sound. I went for acoustic insulation for my garden office.

How to Build a Garden Office - Step 1 - Footings and Floors

Floor Structure for your Garden Office

First off clear a patch of ground big enough for the garden office to fit in, clear of weeds etc, and then use a spirit level and a plank of wood to establish 4 or more level pads (concrete blocks / bricks) on which we will start to build our floor structure. Check the floor structure is square, place an uncut play board on top and use it like a giant set square to check that the office base is square.

the foolish pig?

Remember to make a good job of this stage, even a cheaply built garden office will be fairly heavy come the end. Pads every 1.5 meters is a good idea.

Damp Proofing Floor of Garden Office

Next lay down the cross beam / floor joists , and over lay with damp roof membrane.

space your joists to match your uncut ply board / OSB (saves time)

Insulation and Floor Boards for your garden office

Trim the damp proof membrane around the edge of the floor platform, you can leave this until after puttting down the floor boards, if you want. Then add in the insulation to fill the voids between joists.

 Building a Garden Office - Step 2 - Walls

To build the wall of you garden office you have two choices you can either build the frame for the walls and then attached the external cladding first. Or if in my case you are building close to a boundary the you can make up individual panels with the exterior cladding already attached.

building with panels as above is good when you are in a tight spot

 Things will be a bit wobbly to start off with but once you have made you first corner, things will become easier. Keeping checking that everything is upright using a spirt level.

building a corner means a stable wall section to work from

Extra framing around windows

 Doors and windows for your garden office.

Windows and doors can be sourced fairly easily from ebay, second hand is cheap expect to pay £15 - £50 for an ebay window, or £150 - £350 for a new window. Double glazed will keep the heat in better.

Buy a timber door frame and build this in to the garden office to provide access (hanging the door is probably the most technically demanding part of the whole build!)

Building a Garden Office - Step 3 - Roof

Building the roof is almost the same a building the floor, just put it on top of the garden office, leave an over hang all of the way around so that drips don't run down the walls.

To water proof my roof I used 3 layers of damp proof membrane, get on the roof, with no shoes on, unroll the plastic sheeting over the roof, staple down around the edges. Not easy doing this when windy so try and do it on a calm day.

Inside you garden office

Inside why not make your own desk and shelves with off cuts / spare wood. Cheap and made to measure.

ready for work

OK that is it. In our next post we will observe the set up for the DIY green roof.

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