Rafters 45x95 instead of 45x120

[Derbyboy]

Hello,

I am going to build a cold storage for the grill and bicycles. Do you think I can replace the rafters with 45x95?

Span 1825mm (B1)

 

[fribygg]

Yes.

For the beam you should probably go up a size, and for the posts you can probably choose something cheaper, like two nailed together 45*70.

 

[Derbyboy]

I'm going to use a center beam 45x145

The posts will only be center posts, and I will use 45x95. The outer posts will be walls.

 

[Matti_75]

Won't the posts in the middle be in the way? Increase the dimension of the rafters and remove the middle support entirely.

 

[Derbyboy]

Well probably a bit, but I have to fit the roof under the eave but above a window, so I don't have much to play with.

 

[Marcus_Carlsson]

Interesting question, is there a table that shows what, for example, 45x145 corresponds to if you were to join studs that are not equally high?

For example, say 45x145 --> 2 x 45x95 etc.

I tried doing some googling but didn't find anything.

In America, it seems they do this in some constructions, they join several 2x4/6 instead as we do in Sweden and increase the dimension.

 

[Derbyboy]

Won't the posts in the middle be in the way? Increase the dimensions of the roof beams and remove the middle support completely.

I have reconsidered according to your suggestion.

 

[z_bumbi]

Interesting question, is there a table that shows what, for example, 45x145 corresponds to if you were to put together studs of different heights?

For example, let's say 45x145 --> 2 x 45x95 etc.

I tried doing some googling but found nothing.

In America, they seem to do this in some constructions, they put together several 2x4/6 instead, as we do in Sweden, and size up.

For example
https://www.byggahus.se/forum/threa...x220-vs-70x170-fran-1920.179916/#post-1383615

Since h^2 and h^3, it quickly becomes a ridiculous number of studs, but one or two steps down works. Then there’s the utilization factor.

Sometimes diagonal braces and trusses are not a bad idea.

 

[Marcus_Carlsson]

For example
[link]

Since h^2 and h^3, it quickly becomes a ridiculous number of joists but one or two steps down works. Then comes utilization.

Sometimes diagonal braces and roof trusses are not a bad idea

Aha, I see, but it's the bending resistance that is dimensioned, and it has h^2. Still fun, maybe I'll make my own table...

 

[Marcus_Carlsson]

It is the bending resistance that should be compared, see below. Then in reality, everything is complicated by a whole lot of factors regarding what the actual load will be.

 

[Marcus_Carlsson]

For example
[link]

Since h^2 versus h^3 it quickly becomes a ridiculous number of studs, but one or two steps down work. Then the utilization rate comes into play.

Sometimes braces and trusses are not a bad idea.

Here is the table --->


For instance, 2 x 120 is almost as good as 170.
And 2 x 145 can almost be equated with a 220.
However, it becomes a very heavy and expensive construction if you have to do it this way 😆

But interesting nonetheless.

An extreme case is that 9 pieces of 45x70 is the same as 1 piece of 45x220 (!)

 

[Marcus_Carlsson]

For example
[link]

Since h^2 respectively h^3, it quickly becomes a ridiculous number of joists, but one or two steps down work. Then the utilization rate is added.

Sometimes diagonal braces and rafters are not a bad idea.

Here is the table --->
View attachment 827944

For example, 2 x 120 is almost as good as 170.
And 2 x 145 can almost be equated with a 220.
However, it becomes a very heavy and expensive construction if you have to do it this way 😆

But interesting nonetheless.

An extreme case is that 9 pieces of 45x70 are the same as 1 piece of 45x220 (!)

 

[Derbyboy]

But it doesn't matter how they are assembled, screwed, glued, or written and glued.

 

[Marcus_Carlsson]

But does it not matter how they are joined, screwed, glued or written and glued.

It surely does, but I have no idea in what way. There's probably an industry standard for that somewhere...

 

[Testarn]

But does it not matter how they are joined, screwed, glued, or nailed and glued?

If you mean you're replacing a 45x1xx with two 45x95 where your two 95s have a higher total bending resistance than your 45x1xx? And it's the two 45x95s that would be joined?

As long as the load is evenly distributed on both beams, it doesn't matter if they are joined, but if the load is only on one beam, it will matter. Then they must be joined for both beams to be able to carry the load.

I assume you will have raw wood as the roof, and then the load will be distributed on all roof beams regardless of how close they are to each other. You can have them c/c 300 mm or two next to each other with c/c 600 or every other roof beam with 150 and every other with 450 mm c/c - they will hold equally well.