Green Roof Shed

[Brandlin]

I'm going to be building something I call a "Shed", but SWMBO refers to as a "Summer House" over this summer. We've agreed to call it a Summer Shed. It'll be used for over wintering plants and garden furniture and plants so will have antifrost heat, a potting shed, garden tool storage and generally a place to potter about.

It isn't big, just 3.5m x 2.4m. Going on to an already poured concrete slab. There are a few constraints which are preventing me from doing things the 'usual way', and a few desires.

• The shed is pushed back against a 3.5m tall boundary fence. This means the fall of the roof needs to be towards the front of the building not the rear to be able to access guttering.
• I'm 1.93m (6'4") tall and I WILL have a full height double width entry doors on the long side under the gutter. Windows either side of the double doors, meaning almost the whole long wall is glazed.
• Aesthetically we both like the look with long protruding eaves. So the height towards the back of the shed will be 2.4m to allow for the roof pitch to clear the opening doors.
• It will be located against a north facing boundary so will be quite dark, Windows can only go in the north and west sides of the building. So we are going to add a roof light/sky tunnel.
• The building is below the level of the main viewing point from the house, so rather than look at a metal/felt/EPDM roof we want to install a green roof. probably Seedums to keep the weight down.
• We want an invisible guttering system.

I would be interested in advice and contact with anyone who has worked with green roofs (rooves?) before.

My current design thoughts are:

• Full 4x2 framing on 16" centres. Doubled up in the corners for rigidity and roof loading.
• 6x2 roofing members 16" on centre, located directly over the vertical studs.
• Doubled up 6x2 header across the long wall of glazing. With doubledup vertical studs between the doors and windows for load.
• roof in OSB sheet with perimeter upstand to retain the green roof. EPDM liner.
• Rear wall clad in upvc siding - access to this wall will not be possible so i want to make it as durable and rot resistant as possible.
• Remaining walls clad in shiplap/tongue and groove to be painted.
• Foam insulation board to ceiling and walls, interior cladding in ply or OSB

I am at a very early design stage and just wanted to check I'm on the right lines and am not doing something wholly inadvisable. More detail should emerge over the coming weeks and months.

I'm particularly concerned at the moment about structural loading and rigidity, and rot prevention, especially in the north facing location and under the green roof (no ventilation).

Any advice, suggestions or questions welcome.

 

[MikeG.]

I've done green rooves, reluctantly. For a start, there's nothing green about them. Even the colour isn't green. You have to build a much stronger structure than you would otherwise. In commercial buildings this means bigger foundations and bigger frames.......all that extra steel and concrete is exactly what I meant when I said these things aren't green. You then have to provide a fully working roof, then cover it with all sorts of stuff to keep the soil up there, keep water from building up and so on, and then plant it with stuff which ends up looking like the sort of weeds you see on derelict urban waste ground. What's more, they're out of place. X metres up in the air surrounded by pressed metal flashings and guttering etc is not where you expect to find vegetation.

Your joists aren't big enough for that span, but I am simply not going to get involved in sizing timbers for this construction. It's frankly a nuts idea to pile tons of soil on top of a timber building with a pond of EPDM. The ponding effect you are designing in could actually hold some tons of water before you even add in the weight of the soil.....and this is without knowing the height of the upstands you intend.

I urge you to reconsider.

 

[Hornbeam]

Totally agree with everything Mike has said. If you put all the savings from lighter structure, sedum etc you could probably use something like terra cotta tiles or a weathered copper roof without all the ongoing hassles which green roofs have
Ian

 

[Brandlin]

Sorry you guys feel that way.
I'm not doing this because i believe a green roof is some great environmental statement. i understand it will add considerably to the effort, materials and cost.
I like the look. You don't. That's fine.

I asked for relevant advice. I haven't yet sat down to do a design or any load calculations. I know there is a lot of knowledge and planning to be done - that's part of what i enjoy.

Looks like I will need to go elsewhere.

 

[ScaredyCat]

​
​You could try https://www.enviromat.co.uk/home (not a recommendation, just aware of them) they have a simple guide https://www.enviromat.co.uk/green-roof-installation-guide which might help. I found this one too http://www.greenroofguide.co.uk/media/en/applications/grc_diy_guide_small.pdf. I used to live in Holland for a bit, 10 years or so, and it was fairly common to see houses with this style of roof where I lived.
​
Video too! https://www.youtube.com/watch?v=xHDhWH2r6Dc​

​

 

[Blockplane]

Astroturf over a conventional felted roof ?

 

[RobinBHM]

My father's neighbour has built a garden studio with a sedum roof. I think it looks quite good in a garden setting, which is where such a roof is overlooked from bedroom windows.

I didnt see what size timbers they used, no structural calcs Im sure. 6x2 and 4x2 sounds reasonable, it is only quite small. If falls down though dont blame me

 

[MikeG.]

............ 6x2 ....sounds reasonable........

No. Just no.