Carport rafter dimensions

[Plupp 358496]

I have a pretty good idea of what holds without having built according to building codes every time, and the question is which dimension sags more under its own weight if anyone knows that?[image]

The question itself shows that you don't have a grasp on the situation. Study beam bending theory, and you can answer the question yourself, and perhaps some modesty will arise towards, for example, Swedish Wood's program when you start considering loads, material defects, and so on.

Or do you think there's someone here who knows better than the collective expertise (=the standard)?

 

[ptlf]

It's hard to really understand what is being asked for. The table shows the deflection for different dimensions in relation to your joists and span that you have today

Thank you! That's something like what I wanted to know because it's what they deflect in the middle without any other load than their own weight if I understood it correctly?

 

[ptlf]

The question itself shows that you are not familiar with the situation. Study beam bending theory and you can answer the question yourself, and maybe a certain humility will arise towards, for example, Svenskt Träs program when you start to consider loads, material defects, etc.

Or do you think there's someone here who knows better than the collective expertise (=the standard)?

I do have an understanding of Svenskt Träs program because I never said they are wrong; I only said I have built slimmer than they recommend and it has held. I also asked at the beginning if anyone else had experience using other dimensions than recommended, so I was never looking for approval that it will hold as I intended because I won’t get that.

 

[Grylf]

Correct me if I'm wrong but the program does not calculate the yield limit but the maximum allowable deflection.

 

[Plupp 358496]

Correct me if I'm wrong but the program calculates the maximum allowable deflection, not the fracture limit.

Correct, which is true for many wooden constructions. Of course, other phenomena must still be considered, such as buckling, fracture, creep, etc. But usually, it is deflection that is the determining factor.

 

[Krille4]

I do have some understanding of the Swedish wood program because I have never said they are wrong, I've only said I've built slimmer than they recommend and that it has held. I also asked at the beginning if anyone else had experience using other dimensions than recommended, so I've never been looking to get an okay that it will hold as I thought because I won't get that.

What is the reason you absolutely want to use dimensions that experts don't recommend? Spend a few extra kronor on the right dimensions, and you'll avoid risking your own and others' lives. Plus, you won't have the hassle of shoveling the roof in a normal winter

/Krille

 

[ptlf]

What is the reason you absolutely want to use dimensions that the experts don't recommend? Spend a few extra kroner on the right dimensions so you don't risk your own and others' lives. Plus, you won't have the hassle of shoveling the roof in a normal winter

/Krille

It's not just a few kroner difference if you have your own timber compared to laminated timber.... additionally, it's about the height that I don't want to increase in dimension so willingly

 

[ptlf]

Does anyone know how big the difference in strength is between a regular 45x220 at 4m and a glulam 56x225 of the same length?
There are also finger-jointed ones, do they end up somewhere in between then?

 

[z_bumbi]

What dimensions do you end up with if you have 70 thickness on the studs?

 

[Nissens]

This has held up and 195 should be more stable I think, even if the length increases... it is cc 600 here and I plan to continue with that. I've tried to google but can't find how much pressure different joists can handle

Why do you need cc 600?
Reduce cc until you get enough bearing capacity, then you won't lose any height either.
Then you should probably also check the attachment to the wall, it might be good to put posts as support…

 

[BSOD]

Do you really save anything by having tighter cc if you simultaneously reduce the dimension?

I have a deck and some simple sheds where we deviate from current standards. Sure, it seems to hold, but I would still build around the same dimension that Swedish wood suggests.

 

[ptlf]

Why do you need cc 600?
Reduce cc until you get sufficient load-bearing capacity, then you won't lose any height either.
Then you should probably check the attachment to the wall as well, might be a good idea to add posts for support...

Not a bad idea!

 

[ptlf]

What dimensions do you end up with if you have 70 thickness on the studs?

Have not checked, is something usually used in that dimension?

 

[fribygg]

Har ej kollat, brukar det användas nåt i den dimensionen?

No, it is more cost-effective to reduce the distance between the studs than to increase the stud thickness.

 

[Nissens]

Do you really save anything by having closer cc if you simultaneously reduce the dimension?

I have a deck and some simple sheds where we deviate from current standards. Sure, it seems to hold, but I would still build near the same dimension that svensk trä suggests.

I wrote nothing about reducing the dimension.