Green roof - any experiences?

[shovetheholly]

I'm planning a green roof at the moment, which will be on a cold, north-facing side of my house in Yorkshire where it rains A Lot in winter, but will be quite dry in summer. The tray for the roof won't be that deep (the kind of construction we are using doesn't allow a really deep one), so I need things that can cope with nutrient-poor, part-shaded conditions, that are wet in winter, dry in summer. Bit of a challenge, I think . Not helped by the fact that I have never done this kind of gardening before and have no clue what I am doing!!

I'm hoping to plant it in Piet Oudolf style blocks of different texture/colour.

If anyone has experience of doing a green roof or planting suggestions, I'd be grateful. Things that I have seen growing on walls etc around here that might work so far are:

Persicaria vaccinifolia
Lysimachia nummularia
Adiantum species
Arabis fernandii

sedums???

Sorry to digress but assume you've checked that the structure can take it? They get VERY heavy when wet...

It's a new extension so it's being designed in and fully looked at by structural engineers!!

I think I might contact local alpine experts and see what their advice is. Maybe the Hardy Plant Society too, as they always seem to be trekking in the Himalayas looking for plants!! There will be species out there but my guess is that some will be quite specialist or rare and I might have to grow hundreds of plugs from seed!! I have plenty to of black ajuga in the garden, so that's a start!

Will report back with progress!

North facing is the tricky bit.
My one is very light (there is no soil, just lots of clay granules and then some soil around the actual plants)
and it has sedums, sempervivums and a couple of other tough little alpines
BUT
it faces due south so they get sun all year round

facing north it will get no sun at all for several months of the year
you may be best to go for a moss garden - sounds surreal but could look rather amazing

what I have learned with mine is that nothing survives that is more than twice as tall as the substrate is deep - it is not irrigated in any way.

That's interesting about the height talkin - I suspected that this might be the case.

I think there will be mountain scree plants that grow in shady areas, it's just they probably won't be the kind of thing that's in my local garden centre. I've been taking notice of what grows in the cracks of north-facing walls around me, as I figure the conditions will be the same. Maidenhair ferms, harts' tongue ferns, that ivy-leaved toadflax all seem to tolerate those conditions. Also, rather less promisingly, campion and bloody herb robert, which is the bane of my life. I think most sedums will struggle.

Moss is, I think, a really great idea for the shadiest bit. The house is at a slight angle, so the left hand side of the roof as you look out does get sun in summer, whereas the right does not. There are some beautiful mosses growing really, really well in the peak district nearby, and I don't mind giving them a bit of a helping hand with some mist out the bedroom window if it gets too dry.

I think my first job is to speak to the architects and see about the load that the building will take, because if I can do an intensive roof - i.e. one with more soil - that may well work better than an extensive roof, which is lighter and more scree-like. I think, however, the answer will be that only the extensive one is possible because of other construction requirements (the extension isn't standard brick).