Carport and grass roof

[Buford]

I am going to build a carport. The roof will be covered with soil and then grass, thus becoming heavier than a roof with concrete tiles, I think.

Anyone who has more insight on the situation than I do and can hint if I'm way off base in wanting a stable roof for the carport??

 

[Daniel 109]

How are you planning to construct the roof above the rafters?

 

[Buford]

How do you plan to construct the roof above the rafters?

Tongue and groove boards, possibly tar paper, then a membrane suitable for a sedum roof, some protective layer like landscaping fabric, then soil and drought-resistant grass. Along the edges, I'll place a board on edge to keep the soil in place if it rains heavily.

Planning to build a carport. The roof will be covered with soil and then grass, thus becoming heavier than a roof with concrete tiles, I think.

Does anyone have more insight than me and can hint if I'm completely off track if I want a stable roof for the carport??

 

[VidarH]

Are you considering loose soil under a geotextile or a reinforced substrate mat with pre-grown sedum? I can imagine that a sedum roof supplier might have some tips regarding the underlying construction. I have some memory of there being some type of drainage mat under the green roof at the museum where I helped with the surrounding landscape when I was about 15, 25 years ago, but I could be wrong.

 

[Buford]

Are you thinking of loose soil under a geotextile or a reinforced substrate mat with ready-made sedum? I can imagine that a supplier of sedum roofs might have some tips to offer regarding the underlying construction. I vaguely remember there being some kind of Platon mat under the grass roof at the museum I helped landscape around when I was about 15, 25 years ago, but I could be wrong.

We did a similar grass roof on a shed several years ago, so I think I've got that covered ...
I'm more in need of a discussion regarding the construction that holds up the roof. I'm considering ordering roof trusses if the uncertainty factor becomes too great.

 

[heimlaga]

Normally, two layers of grass sod cut from a grass field are laid. The first layer with the grass facing down and the second layer with the grass facing up. Then the upright grass continues to grow and its roots bind the soil together.

I think the construction looks a bit too flimsy to support a sod roof, but to know for sure, you would need to perform a structural strength calculation.

 

[justusandersson]

Considering that it's outdoors (= climate class 3), I think you should go up to 45x220 in the rafters. 45x145 is too weak as posts in the middle position if there is going to be any height to the roof. Screw together double, go up in size, or preferably choose 95x95 lumber.

 

[Buford]

Considering that it's outdoors (= climate class 3), I think you should go up to 45x220 for the rafters. 45x145 is too weak as posts in the middle position if there is to be any height on the roof. Screw together double, go up in dimension, or preferably choose 95x95 timber.

I had planned to screw together double 45x145 as posts. But a 95x95 might be more stable after all?
I've looked at rafters that seem designed for climate area 2, which have a similar construction to what I intended, but with weaker timber and 1200 between them. For regular roofs then. And they were supposed to handle a span of 4300 (I have 3500). That's why I thought 195x45 and 600 between would be enough. But I also realize that I lack the knowledge to calculate properly. I thought I had gone overboard with it all, but some of you doubt. Thanks for the input, I'll see how I proceed.

 

[justusandersson]

Timber with a square cross-section is always best as freestanding posts because the buckling load is equally large in both directions. I am convinced that your roof construction would hold, but since it is outdoors, one should have slightly larger margins.

 

[heimlaga]

I was primarily thinking about the wall bands that look flimsy. I'm also not entirely sure they can withstand the stamping pressure on the editions.

 

[Daniel 109]

Lumber with a square cross-section is always best as freestanding posts because the buckling load is equally large in both directions. I am convinced that your roof construction would hold, but since it is outdoors, you should have a bit larger margins.

Is that really the case? I seem to recall that 2*45*90 is better than 90*90. But I'm definitely not sure. I will try to look for information.

 

[Buford]

I was primarily thinking about the wall braces, which look weak. I'm also not entirely sure if they'll withstand the load pressure on the rafters.

If I place 2 pieces instead of 1 45x220 as wall plates, does that make a significant difference?

Load pressure and rafters... You lose me there

 

[justusandersson]

Two screw-laminated 45x90 are somewhat better than 90x90 in one direction and equivalent in another. Two screw-laminated 45x145 are also better than 90x90 in one direction and equivalent in another. That's not quite how I expressed myself. I generally pointed out the advantage of square cross-sections on freestanding posts. Additionally, I mentioned two screwed 45x145.

The wall plate can manage well with a 45x220 as the span is only 2 meters. If a total of three 45 mm wide beams in the roof truss interact at the support (on the wall plate), the load pressure will be limited.