Want to grow a lawn on my roof

Posted by: Flame on 13 May 2010

Hi all;

My rooftop garden collection is getting bigger. I am enjoying working on it and it is providing me with a beautiful landscape to sit in. An idea came to my mind today. Could I grow a small lawn on my roof?

To put things into perspective, the villa is built out of reinforced concrete and the roof has been weather proofed and covered with driveway grade ceramic tiles. The available footprint is roughly 45 square meters and of that I'm only intending to cover about 9 to 12 square meters with lawn. My current thought is to build a wooden frame that measures around 3 x 4 meters with a height of 3-4 inches. This frame should house the soil and the lawn on top of it. Still haven't figured out if I need another containing layer at the bottom of the frame or not.

Any thoughts, suggestions or advice based on knowledge, previous experience or plane old common sense is very welcome. Please don't suggest to bring in a professional landscaper to do the job as I really want to do this DIY both for the fun and to reduce the cost. Thanks.

Sincerely.
Posted on: 13 May 2010 by lutyens
Hi Flame
Your problem is that 3-4 inches of soil is not really deep enough! One would normally assume a min of 150 mm top soil to put turf on top of and then that 150mm is above 'normal' earth.

I assume your flat roof is in Riyadh? Here the heat is extreme and therefore drying out will be a real issue as 3-4 inches will not retain enough water. You could irrigate ( hydroponics?) it but that brings its own problems as your local golf course will highlight! And finally it would be very weak in that depth and walking on it would do proportionately more damage than say on that golf course. There are of course stronger and better suited grass for warmer climes but they are much rougher and less the romantic european image of a lawn.

So sorry to dampen your enthusiasm. Do give it ago, which frankly is what it is about but........ I will ask one of my team in my office who are doing some landscape work in the middle east if they have any specific ideas.
atb
james
Posted on: 13 May 2010 by Flame
Really appreciate your input James. Looking forward to the advice from the landscapers.

Regards...
Posted on: 13 May 2010 by tonym
I'd be a bit worried about the weight of soil you'd need on the structure of the building.
Posted on: 14 May 2010 by Richard S
In a temperate climate such as the UK the answer would be to plant a green roof using a waterproof membrane topped with sedum. Many new buildings have successfully incorporated this feature including the Head Office of the conservation charity that I work for; BTCV's Sedum House in Doncaster.

In desert conditions such as yours I would very much doubt that this would work without a great deal of water (and money).

Google sedum to find out more.
Posted on: 14 May 2010 by Flame
Thanks Richard. We have large lawn areas in Riyadh, that are planted with grass/sedum/japanese grass, etc. So growing a lawn in my desert climate is doable and doesn't cost a fortune. In my previous house I had a 30 square meter lawn that grew wonderfully.

From all the input I got and some research which I did, it looks like I must use a layer of water insulation on top of the ceramic tiles. The load on the structure seems to be OK as the lawn is going to coincide right on top of a solid wall in the floor below. What I couldn't find a conclusive answer to is the need for drainage. In europe, a drainage layer is always used. With the minimal rainfall we get here and the very high temperature, I doubt that I will have that much water in the soil to cause flooding. Anybody has an answer to that?

Regards...
Posted on: 14 May 2010 by mudwolf
Proceed with caution. You must have that impermeable layer on top of you tiles. Just think if you get seepage in your ceiling it would all have to be torn out.

I've been seeing green roof projects in the LA Times and other places. They are a high maintenance item. The best one to look at is the San francisco Science museum in Golden gate park done by Piano. I've also seen green walls instead of looking at a bad view or dull wall they have a vertical planting.

I used to be a gardener in my 20s and it was all the rage to do hanging baskets with sphagnum moss and put annuals in for color. My gawd, the amount of water and fertilizer they took and replacing the plants was incredible. Most people didn't have the skill to pull it off and in a year you'd be looking at a half dead thing.
Posted on: 16 May 2010 by Mike-B
Richards suggestion of sedum is a good one - but only for northern Europe, this is a tundra plant - it needs very little substrata so is relatively light

In Saudi, the subsoil will need to be way thicker than 3 to 4 inches, unless you have a constant & continuous irrigation system.
But whatever the irrigation, the water weight plus soil will be significant numbers of TONNES & I seriously suggest a highly qualified structural engineer & an assessment of your water bill as that could be a number of hundreds of litres per day
Posted on: 16 May 2010 by Flame
Well guys. Thank you for all the input. I guess I do have to take matters with a bit more seriousness. I did approach one of the larger landscaping companies in the country but it turns out that they haven't undertaken such projects before. I'll have to either get professional on-site opinion or drop the whole thing all together.

Regards...