[Closed] Sedum roof on shed.

Mines got 4*4timber roof and wall.

With 18mm ply/with visqueen covered with sheet of left over rebar and minimal gravel for a drainage all pointing at a slot in my edge trim to allow excess water to leave the party. with a drainage membrane over that and a thin layer of soil.

Sedums came out of a pot and have thrived to spread planted last spring and should have full coverage this year.

Also have an area near the front that is deeper than the rest and is planted with hanging strawberries and herbs.

Should probably ignore me though. I didn't follow a tutorial so according to those on here I'm doing it wrong and my roof will fail to grow oh and fall down as I didn't follow span tables.

From personal experience the key is ensuring good (I mean suitable for what you're planting) drainage and making sure that drainage doesnt collect anywhere so you have to take the whole ******* roof off and rebuild the stupid git.

I'd also like to point out I was overruled on the design.

Still me fixing the barstad thing however.

I wanted to do this but you have to make sure the shed is strong enough to support the weight. I can't get any more technical than that but I was advised against it with mine

I've done it on my bike shed.
7x2" joists (plenty strong enough for two people to walk about on, even with the extra weight of the roof)
I cheated and made a 'normal' flat roof to make certain it was watertight, sloping very slightly (yes, I know, but technically less than 10deg is flat) On that I made a frame of 2x2, lined with a pond liner, holes at the bottom for drainage. Lightweight gravel (made of recycled glass with lots of air, looks like pumice) layer of old carpets, layer of compost, sedums, job done. Been up since 2016 and no problems at all.

We have one on the flat roof of our bathroom, put there by a builder. It needs weeding once a year as we are under some trees and little shrublets appear. It has acquired some grass and some other stuff, but we let that stay unless it looks like it might try to grow too big.

It is roof boards on joists, a waterproof sheet, vermiculite type stuff, a liner, a bit of compost, plants. It slopes slightly to one end where there is a slotted barrier and a gutter.

The only problem we had was when it filled up with snow one year and a bit of water got round the top of the waterproofing (it is sunken on three sides, with lead flashing overlapping the waterproof).

Mines got 4*4timber roof and wall.

and fall down as I didn’t follow span tables

To be fair... 4x4 are a bloody daft thing to put in a roof 50% of the wood you put up there is doing heehaw.

It probably won't fall down but it might eventually start sagging which would be a shame.

*flashbacks*

More folk who haven't seen it judging.

ItS not going to start sagging - but there are reasons for doing what I did.

Last time folk were thinking I'd used fence posts for a roof.... Mentalists.

To clarify, I really don't care I'm sure it will be fine and i bet it looks ace because chunky timbers always do.

But people will comment because square section doesn't achieve anything other than look good.

but you came across so chippy in your first post you kinda invited some baiting which i should have resisted, sorry.

Thanks for your experiences.
We do get a few snowy days here and that is something that could cause a weight problem.
Will ask our friend who helped build the shed for his thoughts.
Our shed has a very slight slope so there is somewhere for 'runoff' to go.

what depth of rafters do you have Bunnyhop? and where about roughly are you?

We're (I'm Bunnyhop's husband and erector of said shed) between Stockport and the Peak District. The shed is a standard Power Sheds 8*8 pent. Framing is mostly 44x28mm, with some parts doubled up to create 44x56mm. I'm not a very experienced builder but my pal Andy who helped me put it together does a fair bit and we were both quite impressed by the quality of the shed build, even the delivery mechanism (it was all packed neatly onto a single pallet).

The roof is constructed in 4 parts - 2 * 2' x 4' panels and 2 * 6' x 4' panels. Panels are constructed from tongue and groove planks attached to three framing battens, then each 6' panel is joined to a 2' panel using another three framing battens (battens are 44x28x1890mm). The two sections are then placed on top of the walls in opposing directions (so the 2' panels are at either end) then joined together again

It's fairly substantial but I might still use some wood I picked up to construct a brace across the middle of the roof

That's not a huge span. I wouldn't over think it. An extra brace or two will be plenty for the sedum as substrate for sedum can be quite light and doesn't want too much soil. I might be tempted to go a bit heavier duty so it safe to walk around up there, that'll make install easier, as well as maintenance. Maybe 3 8x2 beams.

I used an equal mix of topsoil, perlite and clay chippings. Mine is (from bottom to top) roof - DPM - old carpet - soil mix - sedum. The whole lot has a wooden frame to keep it in place and help keep the soil there while the sedum mat forms. Sedum was taken from walls from friends and family and few garden centre plants. It was pretty sparse to start with but spread to a complete cover pretty quickly.

Having done this to quite a few roofs in that london for rich estate owners to cover their 'greening' policy

I can see no good reason to do it other than you just want to, that in its self is good enough of course

I can see no good reason to do it other than you just want to, that in its self is good enough of course

The bees quite like mine.
Surely it's best to do something with a roof if you can, either plants for bees or solar panels or whatever, tiles or slates or felt do nothing to help anyone

There was a recent report about gardens and how when it comes to wildlife, biodiversity is more important than size. A green roof is a great way to increase your biodiversity. You do need a range of different plants.

Our whole garden is created for wildlife. Putting on a sedum roof covering will be another step to help the bees and insects.

I'm thinking of doing the same but with a span of about 4.5m and am struggling with joist sizes thinking of going for a herring bone joist to make it up nice and strong

The chap who helped put up our shed says a sedum roof would make the inside damp. Surely that can't be the case, otherwise no one would do this.
Any experiences of damp or how to prevent it please.

Its would be damp if you didn't put any waterproof membrane down.

it could get damp becase the roof might remain raltively cool and promote condensation i suppose

I can see no good reason to do it other than you just want to, that in its self is good enough of course

One of the biggest issues in the urban environment is run off, anything that attenuates that is good news for all involved, its cooling, it provides biodiversity, its looks good, its relatively easy to retrofit, the sediment hat accumulates on the roof stays there rather than blocking the surface water drainage... which in old urban areas is normally combined. Combined sewers with too much rainwater in them have to overflow becasue its just not practical to treat the volumes coming in.

No experience of damp at all, mine has been absolutely fine.

These lads provided the sedum and advice for the one I was involved with

Green Roofs Direct

The building roof was a plywood arch, waterproofed and four outlets at the corners.

The chap who helped put up our shed says a sedum roof would make the inside damp. Surely that can’t be the case, otherwise no one would do this.

He's probably not very good at putting up sheds...

Any experiences of damp or how to prevent it please.

There are some very large and expensive buildings with full and extensive green/sedum roofs, none of them seem to be suffering with damp...

Love our sedum roof. Most flat roofs/shed roofs are just ugly - if you're looking down on it from the house why not make it nice to look at

There's a difference between "I'm going to construct a building that will have a sedum roof" and what we have here which is "I've just built a shed, why don't I put a sedum roof on it" If we do just pust sedum on the shed, it will get damp. What we need - I think - is a membrane to protect the shed, on to which we put the sedum

What we need – I think – is a membrane to protect the shed, on to which we put the sedum

Yes, absolutely. I'm in the middle of looking at this for a new shed in the forest near my place.
There are LOADS of guides online for how best to waterproof the roof. Just sticking a sedum roof on to an existing weather proofed roof is going to lead to leaks and damp.
Need a proper waterproof membrane. And some sort of structure to hold the matting/sedum in place.

I considered it for one of our sheds but it wasn't practical as the roof was too weak but found this guide which seems like a good starter even if the 'garden ninja' is a bit of a cheesy alias. For waterproof membrane you can buy the large thick polythene sheets that are used as a DPC under concrete floors from a builders merchant fairly cheaply. I would have thought that would be ideal for the waterproof membrane on a shed.
https://www.gardenninja.co.uk/green-roof-shed-installation/

THanks for that @slowol

Astonishingly expensive things.

I've just looked back through my emails for how ours was built up. the roof was engineered to take the weight, then it had a single ply flat roof membrane on it.

The sedum system on top was installed as follows -
You should have two fleeces.
Normally a Brownish thicker one ( protection )and a thinner black one ( filter ).
1. Lay the Protection layer fully across the roof even up the perimeter upstands if there is enough.
2. Install the gravel stop creating a border to the perimeter, using tinsnips or similar to notch the gravel stop to allow it to bend and form a corner where necessary.
3. Use the joining plates to the rear of the gravel stop to join lengths a form a rigid joint
( the base of the gravel stop should face inward)
4. Install the Evadrain 25mm Reservoir Board ensuring the base of the gravel stop is covered completely.
5. Install the Filter Fleece on top of the Reservoir Board dressing it up the inner face of the gravel stop. ( this will allow water to filter through the slots in the stop, but retain the substrate.)
6. Install the substrate to an even depth of at least 60mm to ensure a successful growth pattern.
( refer to GRO Guidelines available online if unsure).
7. Lightly water the substrate prior to installation of the Sedum Blanket.
8. Install the Sedum Blankets tightly to each other in a staggered joint manner
9. Water thoroughly, and continue to do so every day, especially if the weather remains dry.
( look to keep the Sedum Green, and should it begin to go Red, it is stressed so add water.
This should continue at a rate of around 5litres/ m2/ day for at least 3-4weeks to allow the Sedum to settle into its new environment as quickly as possible.)
10. Weed during this period as necessary, and look for the joins to disappear as the blanket becomes settled and begins to "grow" into one another.

Sedum is hardy and needs little by way of nutrient, but it is considered good practice to sow a few nitrogen pellets on to roof a couple of times a year if the Sedum is looking tired.

Build up is shown here -
https://www.icbprojects.co.uk/solutions/green-roof-systems/sedum-systems
but I can't find the costs for that bit.

the Sedum and substrate came from https://turf.co.uk/sedum-mat. 17m2 of sedum plus 'turf' plus 2m3 of substrate came in at £60m2 (but that was >6 years ago).