Flat green roof

[Dawid86]

Hey!
I am about to finish concrete block walls in my outer building. Next step would be to lay a roof on it.
I am planning to build a green roof. I built a proof of concept on my bin shelter and it seems to work pretty well. So basically i am thinking to build a wooden frame, lower on one side, higher on another, then rafters cut in across, then mdf floor boards, frame around for the soil support, felt it all with torch on covering, layer of gravel, anti root membrane, low organic light soil and then of course vegetation.
I have a problem with figuring out the materials. The shed is a bit under 5m deep, then around 3m wide, with another exactly same size sharing one wall.

On the right side id put a wooden beam across (for bi-folds to be built and fitted later), left side will of course have lintel above the door.
Is that a sound idea? What timber size and spacing would you recommend for it?

 

[Why Not Indeed]

mdf floor boards

Surely at the first whiff of moisture ingress, the MDF is going to go to s***?

Wish I had the space to build myself a shed like this.

 

[Dawid86]

Then i shall go for ply, i suppose 18mm. Good shout.
Yeah i was specifically looking for a house with a big garden. Then again, would it be good to use 200mm x 45mm with 450mm spacing? Or is it an overkill?

 

[Dawid86]

Well another point, the roof run will be 5m so to extend it over the front and back I'd need about 6m rafters. I could not see ones that long so I guess i will have to join two together. If i overlap them and bolt together do you think this will hold well?

 

[bernardgreen]

6m rafters. I could not see ones that long so I guess i will have to join two together

many timber merchants can supply 6 metre lengths. First link from google "6 metre timber beams"

https://www.dgheath.co.uk/product/270/decking-base-timber/tanalised-6m-joist-225-x-50-per-length

look for one closer to the site,

delivery charges may be high for that length, check before ordering.

 

[Dawid86]

Hey! For the green roof would you actually use felt-on or rubber membrane?
Also how would you finish off the edge where gutter sits? I need to of course install some barrier to keep the soil in place but let water run to the gutter. The edge will be around 7m so quite long. I was thinking about metal brackets keeping a long board layed with felt/rubber but then I'd have to screw it to the roof through whatever i use on it, so it makes me a little concerned of that won't rot over time.