How much overhang on floor joists for a porch with a roof?

[Grottulf]

Hello everyone,
I am planning to build a new deck, and for various reasons, there will likely be an overhang of about 1m on the floor joists.
The total depth of the deck will be 4m.
There will be a roof over the entire deck, and naturally, you want the posts for that at the outermost edge.
The carpenter says it's fine, but I'm not so sure...
The floor joists will be 45x170 with 60cm c/c spacing.
With snow load, I roughly calculated that I might have almost 2 tons on each post in the worst case. (The posts are intended to stand with 240cm c/c spacing).

What do you think?

 

[Workingclasshero]

Hello
You should probably upload a picture.
But the principle is that the roof should be connected to the foundation straight down.
Now I understand that this is not how you want to do it, but upload a picture of the construction so we can understand better.
/W

 

[Grottulf]

Hello, I don't have a picture or drawing, but basically like this, but with the lower beam 1m in from the outer edge.

 

[fribygg]

As long as you have a proper plinth under each post, they will handle the snow load from the roof.

 

[Grottulf]

As long as you have a proper footing under each post, they will handle the snow load from the roof.

That's what I don't have...
And that's what this thread is about.

 

[fribygg]

I think you need to show a sketch of your idea. As the footings are placed in your illustration in #3, the footings and posts take the snow load in a sensible way.

Generally, there is very low utilization on a standing post for a patio roof. The footing should be placed directly under the post to support the load.

You can build the floor joist frame completely independently from the roof with a footing row/bearing line closer to the house if you wish.

 

[Workingclasshero]

I think you need to show a sketch of your idea. As the footings are placed in your illustration in #3, the footings and posts take the snow load in a reasonable way.

Generally, there is very low utilization on a standing post for a deck roof. The footing should be directly under the post to be able to bear the load.

You can build the floor framing completely independent of the roof with a footing beam/beam closer to the house if you wish.

Hi
You misunderstand TS, what is desired is an overhang outward from the beam and then placing the posts with a 1-meter overhang from the outer beam.
This means that you must fasten the floor joists to the wall of the house considering the upward forces due to the lever.
The outer beam must be doubled, and the floor joists must be stabilized strongly in a lateral direction, preferably with an outer double new beam that is well anchored to all the floor joists.
Then set up an outer line of posts.
Phew, I think I understood it correctly...
/Workingclasshero

 

[Grottulf]

That it's optimal to have the support beam directly under the posts is quite obvious.

But now the question is how bad it gets with the support beam, and thus the footings, 1m in from the edge...
Or in this particular case, it's not footings but a concrete beam that lies "floating" on a gravel bed.
But that doesn’t really matter.
What is relevant is that the support beam is not positioned at the edge where the posts stand.

I have seen examples of calculations on how to determine the deflection on a plank that is anchored versus resting on something at the ends.
But I haven't seen the same for loading the end of a plank when it is anchored a bit away from there.
But I assume it's possible to turn the calculation "upside down" and make the support beam's position the load point...

 

[Grottulf]

Hello
You misunderstand the TS, what is desired is an overhang outward from the support beam and then to place the posts with a 1-meter overhang from the outer support beam.
This means that the floor joists must be attached inside by the house wall considering the upward forces due to the lever action.
The outer support beam must be doubled, and the floor joists must be stabilized laterally, preferably with a new outer double support beam that is well anchored in all the floor joists.
Then place an outer row of posts.
Phew, I think I've understood it correctly...
/Workingclasshero

Yes exactly! 🙂
I'm not a carpenter, so I'm sure I'm using the wrong terms 😳
But it's not entirely impossible, you think?
An inner support beam for the floor will be bolted to the house's concrete foundation, and we can make sure to bolt the floor joists properly in it, so they can also take upward forces.

Floor joists are the same as floor beams, right?
With a "new outer support beam," you mean the outermost where the posts are going to be, right?
That's to better distribute the forces to the adjacent floor beams, I assume?
So if you can just manage to distribute the forces from the posts holding up the roof, to also load the three floor beams that lie between the posts, it should be fine even with a 1m overhang, right?
(Posts with cc 2400, and floor beams with cc 600)

 

[Workingclasshero]

Exactly! 🙂
I'm not a carpenter, so I'm probably using the wrong terms 😳
But it's not a lost cause, do you think?
An inner bearer for the floor will be bolted to the house's concrete foundation, and we can make sure to bolt the floor joists properly to it, so they can also handle upward forces.

Floor beams are the same as floor joists, right?
With a "new outer bearer," you mean at the very edge where the posts are supposed to stand, right?
That's to better distribute the forces to the adjacent floor joists, I assume?
So if you can just manage to distribute the forces from the posts holding up the roof, to also load the three floor joists that lie between the posts, it should be fine even with a 1m overhang, right?
(Posts with cc 2400, and floor joists with cc 600)

Hi
It seems like we're thinking the same way, yes!
I can't say if it will hold, but is there an option to use 220 floor beams/floor joists?
Of course, there's the possibility to place the floor beams closer together, double or triple or use laminated beams where the post is supposed to stand.
There's another thing, making sure it holds is one thing, but making it feel stable is another.
This is the wrong place to skimp on sizes, it doesn't cost much more in the end!
/W

 

[fribygg]

You should not load a floor joist 45*170 with a 2-ton load from the ceiling one meter from the bearing, it will not hold, and the floor joist will break.

 

[Workingclasshero]

You should not load a floor beam 45*170 with 2 tons of weight from the roof one meter from the support, it will not hold and the floor beam will break.

Or the attachment inside towards the house wall will lift.
/W

 

[Grottulf]

You should not load a floor beam 45*170 with 2 tons from the roof one meter from the support, it will not hold, and the floor beam will break.

That sounds reasonable.
But then the question is, where is the limit?
If you manage to distribute the load with an external support beam so each beam "only" carries about 500kg?
(I realize that you can't distribute the force perfectly so 500kg might not be entirely realistic)
and you block the floor beams over the support beam they rest on, so they can't twist?
It might be a lost cause regardless, but how large of an overhang would be acceptable?
50cm? 25cm? 10cm?

It would be interesting if someone would have the desire to do a calculation on a cantilever setup for a single lying 45x170 beam on edge.
So you get a sense of what a single beam can handle, and then make an assessment of how much stronger the completed structure becomes...

I have done such calculations for steel beams, but that was probably around 30 years ago, so I've forgotten most of it.
And my Björk's formula collection is probably gone a long time ago...

Regarding 45x170, I'm somewhat limited to that to not have the floor too high up.
I want it against the foundation, and not against the wooden siding.

 

[fribygg]

Regarding 45x170, I am somewhat limited to that to avoid the floor being too high.

You should consider laminated wood or steel; regular wood is not going to manage it.

 

[fribygg]

It would be interesting if someone would be willing to do a calculation on a cantilever assembly for a single horizontal 45x170 beam on its edge.
So you get an idea of what a single beam can handle, and then make an assessment of how much stronger the finished construction becomes...

It's probably faster and easier to set up such a beam and load it down until it breaks.