"michael adams" wrote in message
...

"Uncle Marvo" wrote in message
...


Good point. The only problem then would be a) getting the thing on there
in
the first place and b) weeding it. How do the Norwegians, who do lots of
this, manage their weeding? I had assumed that sedum or whatever they use
is
short growing stuff which beats the weeds. Maybe not.

Perhaps I'll use astroturf!

Rockwool was mentioned in my previous link.

Used extensivley in hydroponics, and presumably very light.

How it's anchored so as not to slide off, and how the plants are anchored
in the rock wool until they get established is another matter.

http://www.grodan.com/sw63706.asp

From the link it looks as though rockwool is pretty substantial
though light, like expanded polyurethane or very thick loft insulation.

Why not try using two or three slabs of rockwool which can be planted up
on
the ground, and when fully established lifted into position ? If the slabs
were on top of plywood or chipboard sheets on the ground, these could be
then
lifted up and the rockwool blocks slid off onto the roof. You'd still need
some means of anchoring the rockwool on the roof however.

I have a fair lump of rockwool, used as loft/boat insulation. It might be a
bit thick. I'll experiment with planting some stuff in it. I think grass
might be one good bet as it doesn't disappear in the winter, also it keeps
down weeds if you use the right stuff.

I think the loading would then be quite low as long as it is well-drained. I
suspect that it can be kept on the roof by means of some spikes, so I need a
material that is waterproof and spikey. Can't think of one.