Roof strong enough for a tank? How do I estimate before our sedum roof?

[Elitost]

I have started building a shed 4.8*3 m which will have a homemade sedum roof, similar to https://kristinasoas.com/2014/10/10/hur-vi-fixade-ett-gront-tak-sjalva/

In the attached sketch, I am planning for cc-measurements 60 with a lower chord that rests on the walls (95*45 studs). The lower chord of the trusses is 195*45 and the rest is 170*45. It feels like it could support much more than I intend, but someone with experience is welcome to provide some input on whether I am on the right track or not.

 

[wildeside]

Just calculate it, modern sedum roof weighs 50kg/sqm water-saturated

 

[Elitost]

Just count on it, modern sedum roof weighs 50kg/sqm when water-saturated

I've been searching for a simplified formula to calculate what the construction can withstand, but haven't found any. Svenskt trä has examples in its design guide, but none of them are comparable to the shed I'm building.

Do you have any suggestions on how/where I can search to get a "rule of thumb" answer?

 

[wildeside]

Maybe not the easiest, but there's quite a lot of info about roof trusses anyway
https://www.svenskttra.se/siteassets/5-publikationer/pdfer/st-th-2021.pdf

 

[wildeside]

Another solution to your problem
https://www.adlibris.com/se/bok/tak...OCskpEl5lN8D7VJYj6nB0eokK1ehLRboYwUhQoJfD_BwE

The times I need a calculated roof truss, I usually get quotes on the trusses.
Although a bit different with your build that is not so large.

Let's hope that someone with the program and/or knowledge helps you here on the forum.

 

[myrstack]

I built a shed the other year with a sedum roof of about the same dimensions as yours, and while I indeed have a pent roof, I went with 45x145 cc-600 after checking the thread guide. I find it really stable, and considering your roof truss dimensions, there shouldn't be any problem. The books mentioned earlier along with the "träguide" are recommended, and some of their sheds should be similar to what you're considering, so you can see that you’re on the right track.

When I insulated, however, I used 120x45 as a wall stud to accommodate either thicker insulation.

 

[Elitost]

I built a shed the other year with a sedum roof with approximately the same dimensions as you, and although I have a mono-pitched roof, I went with 45x145 cc-600 after some checking on the thread guide. I find it really stable, and given your dimensions for the trusses, there shouldn't be any problem. The books mentioned earlier along with the träguiden are recommended, and some of their sheds should be similar to what you're envisioning, so you can see that you're on the right track.

When I insulated, however, I used 120x45 as wall studs to fit thicker insulation.

Thanks, that's great. It sounds like my dimensions have some margin (and they surely can have that).

I'm largely basing it on the träguiden's garage but slightly scaled down. I've previously received support regarding timber dimensions for the floor framing and framework, so I feel confident there too. I've put insulation in the floor but don't really plan to insulate the rest, so 95x45 should be enough.

What dimension of raw planking (or board) did you use on the roof?

 

[Workingclasshero]

45x145 is enough for the trusses, and so is 45x95.
Consider if it might look a bit bulky with trusses that thick?
If it looks like you want it to, go for it

Good luck
/W

 

[myrstack]

Thanks, that's great. Then it sounds like my dimensions have some margin (and they can well afford to have it).

In many ways, I'm basing this on the wooden guide's garage, but a bit scaled down. I've previously received support regarding the timber dimensions for the floor structure and frame, so I feel secure there as well. I've put insulation in the floor but don’t really plan to insulate the rest, so 95x45 will suffice.

What dimension of raw board (or sheet) did you use on the roof?

I used 20mm if I remember correctly and then underlay felt on top of that and a medium-quality dust sheet before the water-retaining felt that the sedum mats were laid on. I only have about a 7-degree slope so in my case, the sedum stays put without any slats at the roof edge.