Build a Living Roof / Green Roof

Make a normal flat or sloped roof into a beautiful living garden.

While redeveloping our house we decided to install a living roof on our kitchen roof, why you ask.. well..:
1. I liked the idea of having a bit more greenery in the property (we live in central London)
2. We wanted somewhere for some wildlife to have (bees etc)
3. Insulation - green roofs are brilliant at insulating, both keeping heat in and cold out

Read on for how we did this

* As usual and mentioned millions of times on here - I take no responsibility for anyone following this and any maiming, death or damage which follows; nor world war or anything else :)

After doing quite a bit of reading on the Internet, ok well an afternoon or so, I soon realised that there isn't a step by step instruction for building a roof garden, just lots of greenies saying how good they are, and lots of companies trying to sell you expensive stuff to do it - so i thought I'd give it a go myself.

Before putting anything on a roof you need to make sure its strong, very strong.
As we'd just had this roof made we ensured we'd had is strengthened - there are 10 joists under the roof, each bolted next to another joist and supported by a steel frame at either end - so its super strong just to be sure. 

I found online is that living roofs can weight anything up to 150KG per SqM, so I asked our builder and engineer to work to a dead weight of 150KG - whats a 'dead weight' I hear you ask - well.. thats the weight it'll be when there is just itself up there, a live weight is stuff like water (rain), snow or the bloke on a ladder trying to install a satellite dish.

All set? Roof ready, then read on!

There are a number of types of living roof, ranging from the one I've made (enough for some simple grass, plants and anything else that comes along, right the way to full on living garden worlds, with trees, ponds and more - this isnt what we're after!

To keep the plants happy they need:
* - Soil to sit in
* - Some way of staying moist enough when it isn't raining (ideally we want this garden to be maintenance free)
* - Drainage so they dont get too wet (plants are tricky things to keep happy!)

Also you need to protect the building structure, so this is my recipe for making a living roof:

* - 1 x Roof - it'd be a normal garden if it wasnt on the roof!
* - 0 x Insulation - I had to put in some thermal insulation because our council building control couldn't calculate the U value for insulation of the living roof - after installing it this is way better than any fibreglass or fibrespan board - so you probably dont need this!
* - 2 x Pond liner  - this is to stop any of the roots, damp, greenery, water or any other stuff getting to the roof - I used 2 x liners to be extra safe
* - 1 x Root membrane - fancy name for the stuff you get in garden centres that stops weeds growing under decking/paths - This stops the roots and mud getting to the lower level of gravel, to help drainage
* - 2 x Gravel - A layer to go on top of the pond liner, and another to go on top of the root membrane
* - 1 x Moisture blanket - this is to help keep moisture in the soil - i used blankets used in hanging baskets, but they cost a ton - you can also use cardboard or old blankets - however I was concerned these may rot
* - 1 x Wood chips - More soil moisture goodness!
* - Compost - Food for the plants
* - Top soil - gives a bit more substance to the compost
* - Big stones to help with drainage at the edge and stop plants growing into the building
* - plants!

I started with a fully functioning roof with felt already sealed on it, therefore I havent worried as much as you would need to do if doing this on a leaky roof.

The insulation was required by our local building control, but I dont believe this was needed - however if you want a SuperRoof! stick some on it, it cost very little and was the silver backed bubble wrap you get in building merchants.

So, the steps:
1. Roll out insulation on the roof and cut to size - nb:/ i did this on a very sunny day (yes we do occasionaly have them in London!) and it was blinding standing on a silver roof!
2. Roll out pond liner number 1 taking care to tuck it under any leading you've got at the edge of the roof - so rain water comes off any walls, hits the lead and then goes inside, rather than under, the pond liner
3. Once pond liner #1 is rolled out cut off any spare (making sure you've left a good 5 inch lip around the edge of the entire area
4. Use the cut off's to go under the area your roof drains to - in my case this is a drain off the side
5. Repeat the same with liner #2

This bits easy

1. Pour on the bags of gravel - your looking to get just a single layer cover over the entire roof
2. Brush into place
3. Roll over the root membrane
4. Add some more gravel - I went for a layer of about 1.5 x the one under the root membrane (didnt get a photo of this sadly - close your eyes and imagine!)

Now onto the soil and compost goodness!

1. Roll out the moisture blanket keeping a 6-8" space around all of the edges (I have read you can use old towels/cloths/sacks to achieve the same effect, basically this is to get damp and stay damp)
2. Put another layer of small stones over the moisture blanket
3. Put large gravel or pebbles around the edge of the roof in the space you've left - this is to ensure drainage at the bottom, and also stop the plants growing into the building
4. Use flashing tape (lead replacement self adhesive tape) to seal the pond liner to the edge of the building where there is no flashing - this makes sure that no water gets under the pond liner

Finally moving onto installing the growing stuff!

1. Lay out the bark on the roof - this is another layer of damp goodness to stop the soil drying out too much (when buying the bark make sure its not chemically treated to stop weeds etc, as this will not be good for the plants!
2. Once you've got a good covering of bark start to put the compost up. Easiest way I found was to put it into 5 piles then gently (making sure not to move the bark etc) rake it around
3. Do the same thing with the top soil
4. Give it a gently bit of turning to mix it up a bit
5. Get stomping, you want the soil to be reasonably firm - not fluffy and light 
6. Final thing to do is put some paving slabs up - this is for two reasons, 1 - so you can walk around without treading on your plants, 2 - so you can put a ladder on the roof to get to the higher one if needed - otherwise you'll put the ladder on your living roof and may damage the liners etc

We visited the local garden shop and picked up a selection of plants that are hardy (see the bottom of the post for details).

Before planting I placed the plants around to get a feling for the spacing.
Once the spacing was right then dig a hole and bed them in.


Plants we bought:
Name / Notes
* Chamomile - Has spread ok
* Houstonia Caerulea - Has spread ok
* Sedum Hispanicum Glaucum - Brilliant, looks great, spread really well
* Sedumm Reflexum - Brilliant, looks great, spread really well
* Thymus Serpyllum Minimus - Favourite, really dense coverage, very pretty
* Scabiosa (Misty Butterflies) - dont like, looks a bit weedy now
* Acaena Saccaticupula (Blue Haze) - Didnt last too long
* Cotula Hispida - Didnt last too long
* Dianthus Deltoides (Acctic Fire) - looks lovely, but hasnt spread that well

All of the plants have now been in for well over a year, sedum really is the way to go. 

When planting keep them in sensible patches and let them spread

Now that this has been installed for well over a year I've got some conclusions:

1. It works - woop!
2. You do need to weed it during the spreading process (ie while the plants you want are filling the gaps in) - I've done this 3 times this year, doesnt take more than 10 minutes
3. You do need to water it - as I'm lazy I've installed an irrigation system (cost £17 on ebay), this connects to an outside tap, turn it on for 30 mins every few days or so when its very sunny - this could run off a rain water supply if you wanted.
4. Some plants take far better than others - I've started to move around the plants that work to get a better spread. By next year I want the whole thing as wild/maintenance free as possible
5. We've had bees - which is great!

Let me know how you get on