mono-pitch roof loads

[slugboy6000]

Hello,
I'm a curious builder hoping to understand the load profile of a mono-pitched roof addition (something like the image below).
My primary concern is correctly sizing the horizontal beam which supports the rafters (high snow loads here), but I don't know how to calculate the distribution of weight between the ledger board (on the wall) and the beam. I have a good understanding of flat deck construction, but how does beam load change when these structures are given a pitch?
Some contradictory information has me puzzled.
Thank-you

 

[PI31415]

For a simple span rafter with a uniform distributed load, the slope of the rafter will not affect the loading on the beam (assuming adequate shear connection to the ledger) except the dead load will be slightly increased due to a slightly longer rafter. So, to answer your question, for a simple span rafter with a uniform load, half the loading on the rafter will be transferred to your ledger and half would go to your beam. In your attachment, you show an overhang, so depending on the dimensions, this could definitely change the loading on the beam significantly. However, without span/overhang dimensions it is hard to tell to what extent this will affect your beam loading.

A few additional notes:
The slope is important for calculating snow loading, so make sure you take that into account.
Also important to consider is the drift loading or sliding snow that results from being up against another structure; that will be critical for sizing your rafter and beam.

Woodworks: Tutorial for Understanding Loads and Using Span Tables has some information that you may find helpful.

ENG Tips Discussion: Rafter Loading is a relevant conversation you may find interesting.

 

[slugboy6000]

For a simple span rafter with a uniform distributed load, the slope of the rafter will not affect the loading on the beam (assuming adequate shear connection to the ledger) except the dead load will be slightly increased due to a slightly longer rafter. So, to answer your question, for a simple span rafter with a uniform load, half the loading on the rafter will be transferred to your ledger and half would go to your beam. In your attachment, you show an overhang, so depending on the dimensions, this could definitely change the loading on the beam significantly. However, without span/overhang dimensions it is hard to tell to what extent this will affect your beam loading.

A few additional notes:
The slope is important for calculating snow loading, so make sure you take that into account.
Also important to consider is the drift loading or sliding snow that results from being up against another structure; that will be critical for sizing your rafter and beam.

Woodworks: Tutorial for Understanding Loads and Using Span Tables has some information that you may find helpful.

ENG Tips Discussion: Rafter Loading is a relevant conversation you may find interesting.

Thank you for the explanation and the links which were also very helpful.
It's sobering to learn that my intuition was very, very wrong.

 

[slugboy6000]

A quick follow up question here...
Does anyone have any book recommendations for beginners to learn more about wood frame engineering principles?
I noticed that "Design of Wood Structures" by Donald Breyers was mentioned in one of the links.

 

[LittleInch]

One thing I noticed was the bearing of the joists.

You probably need to use joist hangers or place your ledger board attached to the house under the rafters so that they rest on it, not relying on screws or nails in from that board.

That double beam is a bit odd as well. Any bending or misalignment of either plank or rafter and one of those planks will take more load than the other.

 

[slugboy6000]

One thing I noticed was the bearing of the joists.

You probably need to use joist hangers or place your ledger board attached to the house under the rafters so that they rest on it, not relying on screws or nails in from that board.

That double beam is a bit odd as well. Any bending or misalignment of either plank or rafter and one of those planks will take more load than the other.

That image is not my own, sorry for the confusion. It does have problems.
I will definitely use joist hangers. The double beam will be unified and notched into and bearing on what will be 2x6 posts.