Has anyone attempted to grow a garden on the rooftop of their home? I'm considering to do just that: grow a 30 m2 patch of grass on the roof top. For both heat insulation in summer and to have a nice garden there. Some potted plants around it, and it can look very nice.

Wouter.

Hi Wouter,

Yes, well, I've thought about it, but haven't got round to trying it yet.
I read a recent article about a professor at HKU who grows gardens on roof-tops on the HKU campus, mainly for the purpose of insulation - in both summer and winter - and saw a recent tv programme showing how popular such gardens are in Japan.
The actual mechanics of it; layers of insulation, then special light-weight soil, plus drainage, make the whole thing look a bit complicated, or, if you just ask someone else to do it for you, then it looks a bit expensive, but if there were several people on Lamma interested it would certainly create some motivation to find out more details.
As a, hopefully, cheaper alternative, I had wondered how much it would cost to cover a roof in Astroturf/Plastic grass and whether this would insulate as well as a real garden.
Do you have a practical plan for growing your grass - i.e. what to lay and where to get it from? Please let us know any details, if you go ahead with this.

Denis

Denis,

Now I don't really live in Lamma (Lai Chi Shan is near Tai Po), but it's still a village house. And I'm posting here mainly as it's the only English HK-village-related forum I know of.

I have been looking into the matter already on the Internet, and there is some Dutch company that provides all kind of fancy systems. The big problem is drying out of the soil (especially under Hong Kong's sun) on one hand, and the weight on the other hand.
First you start off with a root-blocking layer (unless you don't care about your roof), then a draining/water holding layer, then a soil substrate, and then the grass. Some more layers than this actually but not too bad.

We have asked two garden centres near Sai Kung already, one may be able to do it, the other says they tried and failed. Drying out of the grass is an issue. And with all the gardeners and tree-huggers on Hippie Island I hope to find people who actually did it, to get some experience.

Cost of having it done for a 30 m2 (300 ft2) garden would be approx HK$30-40k according to that garden centre. Not exactly cheap but managable. Considering such a garden easily weighs 300 kg/m2, this means you have to carry up 6 ton of material to your rooftop. That is already something I'd rather avoid!

Wouter.

Thanks for the info, Wouter (and sorry about not knowing where Lai Chi Shan is - I get a bit provincial, living here).

I'll try and get some info from HKU about sources of the materials. Maybe the professor in question would like to continue his experiments on volunteer roof-tops? (Dream on).

I'll get back if/when I get more info, but I'll keep checking here to see if anyone of longer standing (than me) on Lamma adds to this thread.

Regards,
Denis

I have investigated the weight issue, as my downstairs neighbour was getting nervous about the weight of stuff on our roof. I have a nice file of e-mail correspondence showing the Hong Kong Government's superb skill at passing the buck.

My initial enquiry - how much weight is reasonable for the roof of the typical village house - was addressed to the Housing Department. They referred me to the Buildings Department, who informed my that "your enquiry relates to NT exempted house which is controlled within the jurisdiction of the Lands Department." I then contacted the Lands Department, who gave a lot of details of the specifications relating to size etc, but could not comment on weight loading, and I was referred to the District Lands Office (Islands). This office finally told me what I needed to know - namely that I should employ a private structural engineer if I want to find out.

I want to construct a seat bench around the wall which doubles as a planter - sort of a step shape in section - I was considering whether to have the framework in brick or wood.

Wood will eventually rot, but it would be a lot lighter than brick or block. I'm also wondering if a typical village house roof could take the strain of a "low wall" built away from the supporting sides.

Does anyone know of a lighter material that could substitute brick? or does anybody know the weight limit on concrete that maybe has not been properly reinforced ?

Ofcourse, only a structural engineer would be able to give definitive answers, but pointers or views from experience would be nice. On the subject of structural engineers though - anybody know one that wouldn't charge a fortune?

Not sure if it will help.
But on the top of an old style house I installed a jacuzzu on a cement plinth surrounded by brick which when fully loaded with water & 2 people must have weighed in excess of 1,000 lbs in an area about 6' x 6'.
Think you'll be okay with your brickwork "seat" - just make sure yr landlord doesn't mind.

Water weights 1 tonne per cubic metre. People weigh less, depending on their fat content. That's why we float

So if your jacuzzi is 1 metre deep, it weighs 3-4 tonnes when full. (6-8000 lbs).

There you go - told you it was more than 1,000 lbs - thanks Alan

Thanks everybody for the advice.

I was just thinking - in terms of the jacuzzi - wouldn't you also have to consider harmonic resonance with two people inside? - remember galloping Gertie?

Has anyone ever tried three in a jacuzzi?

I'm sure they have