Gable roof framing, what size rafter?

[sbishop]

I was wondering what size of rafter would someone recommend, should I use a 2x6 or 2x8? the lumber is rough!

my roof pitch will be a 9/12, run is 11', 24"oc

i am in snow country, NB Canada, only a few hours from Maine

Thanks for any suggestions,

Sbishop

[Jim_Rogers]

As each piece of lumber put into a building is named by it's location, you have given this piece a unique name that could be confusing people. (I know it's confusing me).
Do you want to know the size of a rafter or a joist?
A rafter makes up the roof plane, a joist makes up the support of the floor.
If your joists go on top of walls level then they are ceiling joists.

Telling us you're in snow country doesn't help much either.
You need to know the snow load for your area.
We can usually look that up via the Internet if we know what state, county or town the building will be constructed in.

With the known pitch and run, you can adjust your spacing to accommodate standard rafter or joists sizes. Or you can adjust your rafter or joist sizes to maintain a common spacing.
There are several ways to do this.....

Jim Rogers

[sbishop]

Jim, thanks for helping out by making sure i'm talking about the right thing. I made a change to my post. Does my question sound right now?

Thanks
Sbishop

[Jim_Rogers]

You questions are right now.

Does someone know the snow load for this area?

I don't have a link to look it up.....

Jim Rogers

[moonhill]

There must be a chart somewhere.  Aroostook County had some kind of record snow fall this past winter 8'-9' on the ground, it just melted with yesterdays heat.  But really, do the snow charts take a average and plan for the 100 year storm?  I know here on the coast this winter I had to plow more than I had in the past 10 years.  Over on the tfg forum there is a picture of a failure due to snow.  A poor repair maybe. 

Another thing with 100 year storms and 500 year floods as the mid-west is seeing, 200 years ago there was no farms to speak of and if there had been a flood of such proportions there would of been no infrastructure to damage and there fore no big deal. 

The rafter length is 13'-9", with out the charts 2x8's, I would use.  Lets see what the charts say.   Tim B.

[Don P]

Need a species and grade and snow load info.
I think snow is done on a 50 year storm. I know they revise each time there is a catastrophic event. You can have 500 year events back to back  ;) They just do the best they can in a real world.

To give some codebook info that may not be even close...
70 psf snow/10 psf dead load, 24" oc, #2 SPF
2x8 max span 8' 9" horizontal  run
2x10 10-8
2x12 12-4
That's in dressed stock

[moonhill]

Hi Don, these things always intrigue me.  So if those numbers are for a horizontal member if it's raised on one end and becomes a rafter can one use smaller stock than listed?  And with steeper pitches can the length be increased even more with the same size stock?  There must be a point where length demands a larger member or course.  With the same run and by only increasing the roof slope the rafter gets a bit longer.  At some point the member becomes vertical and that is a whole different pot of beans.    Tim B.

[Don P]

It was not treating the rafter as a horizontal member, it was taking the measurement horizontally, the run. Yes you can start to play in that math at some level, it typically isn't done in residential. The roof gets steeper and sheds snow but the rafter just got longer so it kinda balances out. You can also look at the rafter as a column with a load on its side bending it. Dead load should technically be taken as actual area live as the horizontal run. In practice I don't see that done often, they usually just fudge a bit heavy on dead load and use the same area for both tributary loads.