Spanning a roof from one floor to the next

[scuba_dave]

Not sure if I phrased that correctly
Below is a picture
Th roof will go from the wall on the right
Where the (17') & (19') markers meet will be the attic wall
To the right will be a cathedral ceiling
So two sets of rafters will meet on that wall (2x6)
The rafters coming from the peak = birds eye & they sit on the wall
The rafters will be cut off allowing a 2x12 to be nailed on the end as a "ridge beam"
The rafters coming from the bottom will then attach to this "ridge beam"
Is this the right way to go about this?

Supporting beams have been engineered to hold the weight
It's just a matter fo best way to make the connection
The roof may not be a "straight" shot as shown
The angle may change slightly at that wall where the rafters meet

The lower drawing was an initial design
But I'd rather have the continous roof
Future plan is for a solar panel array
Note: Pics are reversed from each other

http://i4.photobucket.com/albums/y105/Daveywb/Home%20Stuff/Sideview.jpg


http://i4.photobucket.com/albums/y105/Daveywb/Home%20Stuff/Additionroughoutline.jpg

[CraigFL]

Why wouldn't you just sister the new rafter ends to the old so the load would be carried straight down through the wall rather than offset?

[pushkins]

Why don't you build it like your original B site elevation drawing ? It would look much "cleaner"

[Fischer]

Why don't you build it like your original B site elevation drawing ? It would look much "cleaner"

I guess I would go with Pushkins on this. Not only would it be easier, but it would allow you to put some clearstory windows on that side allowing for naural light. Put you at about a 5/12 pitch, which would be much easier to roof and maintain.

[scuba_dave]

This is an entire new addition
Everything will be new
I want one roof line going from the back all the way to the peak
The rough sketch w/colors shows 2 roof lines
Redesign went with one straight roof

The line where the 17' & 19' marker meets is a wall going straight up
On top of this wall the rafters will meet
I was planning on:

The rafters coming from the peak = birds eye & they sit on the wall
The rafters will be cut off allowing a 2x12 to be nailed on the end as a "ridge beam"
The rafters coming from the bottom will then attach to this "ridge beam"


But some people say the rafters should cross (offset from each other) & be nailed into each other. Doing it that way means the plywood won't quite line up on 16's

The wall shown faces West, single windows have been changed to 2x mulled windows. The 2x French doors now have a 3rd door. The wall to the right faces South & is a wall of windows. Plus the skylights. So I'm going to have a ton of light :)


So.......nail rafters together ?

or

Rafters in line from top to bottom ?

Maybe this shows it better
Black line going up to left is attic roof
Purple going down to the right is great room cathedral ceiling
Brown is the attic wall, supported by 3x engineered LVL
Green is flat ceiling in cathedral ceiling in great room
Attached to collar tied to tie rafters in

Attic rafters will stop on the wall
The blue line is an end view of a 2x12 nailed across the ends of the attic rafters. This 2x will sit on top of the attic wall (brown)
The rafters from the great room will then attach to the (blue) beam - using it much like a ridge beam

Confused now? :D
Clear as mud :lol:
(My drawing skills are off, roof line should be straight)

http://i4.photobucket.com/albums/y105/Daveywb/Construction/Roofline.jpg

[pushkins]

Ahhhhh....It was clear as mud but now I underkustumble (I love that word).

Yes your plan is much clearer now, I thought the black and purple lines were going to be different roof pitches and that would look funky.
You probably should add a ledger board to the side of the attic wall (2x6 wall) for the purple rafters to sit on (this will make your job of installing them MUCH easier as well).

You can still nail the rafters together as they sit on the attic wall, the size of the roof includes the soffits on either side, it just means that where you might have started a sheet of sheathing on the soffit then going 16" to the next rafter, once you reach the attic wall (joined rafters) you will have to travel 1 1/2" less (or more depending on the orientation of the rafters) before you get to your first rafter. 1 1/2" extra travel for sheathing on the soffits is OK.

Is that kinda a muddy explaination ?

For example: 20' wide building would have a 16" soffit on either side making the roof span a total of 272". The first sheet laid on the bottom section would span 16" from the outside of the facia to the center of the first rafter.
Now on the upper section of roof (where the rafter are nailed on the inner side of the lower rafter) the distance from the outter facia to the center of the first rafter would be 17 1/2".
It usually means that you use some extra sheathing as there is a little waste on the upper section as a full sheet is 96" and you will need 97 1/2" so obviously the first row upward sheets will need to be cut down to 78 1/2".

Is that less murky ?....http://216.130.168.108/images/icons/icon10.gif

[scuba_dave]

OK, makes sense.
Something else I just thought of
The rafters will be 2x12's to allow R38 insulation
The "ridge beam" would need to be 2x10 to allow air to flow up the roof between the rafters for venting. - soffits & ridge vent

Ledger board is a good idea
The rafters are going to be heavy, spanning about 16' 6", 16" OC using 3/4 plywood. From plans this is to code, but I've always gone above code. I'm just wondering if the roof will be "stiff" enough
Even the "worst" wood in the span tables will span 17.5' without a problem (L360)

[pushkins]

You will have to make sure that the 2x12 rafters sit higher (not lower) than the top of the ridge beam to allow the air movement over the ridge beam.
3/4' ply will work very well, is ply what code calls for or OSB ?

[Fischer]

Dave,

If you're worried about the weight that will sit on a ledger you can use a product called ledgerlock available at HD. They're 1/4 lags that easily drill into wood without a pilot hole, and are rated stronger than 1/2" lag bolts and meet code for shear strength. That's about all I use for decks, timbers and anything up to 2 1/2" thick. Easy to put in and ACQ rated. They now have them in bigger sizes up to 12" long for other projects. Highly recommended for your application

[scuba_dave]

Since I'm a one man team I prefer plywood over OSB. Gives me a little more time for roofing. I use weatherguard all the way up the roof. So I cover the plywood fairly quickly. I could go down to 5/8, but planning a solar power setup at some point

I had the same roof setup on my sunroom, but I went with 2 roofs
I wish I had made it a straight shot. The inspector wanted lag bolts on my "ridge beam", since the 2nd floor was under construction too I was able to go right into studs. I've seen the timberlock & ledgerlock itmes. Same idea as the Trusslock for the LVL, great idea - Thanks

Went back & double checked my lumber & the span tables AGAIN
The 2x12's can span 18' 6" Max, I'm only spanning 16' 6"
That's with L360 & 50 psf snow load, I'll actually be better then L480
I've been a little over concerned about this roof, I just want it to stand up to a major snowstorm. I'm feeling much better now about the roof

I'm also thinking of adding a strut (new red line) as additional support
That will depend upon the lengtht the strut would be. On my sunroom it would have been maybe 10-12" - more trouble then it was worth

http://i4.photobucket.com/albums/y105/Daveywb/Construction/Roofline-1.jpg

[pushkins]

With a ledger board in place for the 2x12 rafters that strut would be doing nothing.

[scuba_dave]

Ok, I tend to over-analyze
Maybe I need to explain the distances?
I was thinking it would help support the weight
IE where it "supports" (meets) the rafter may be 2' out from the ledger board. The green line will be about 4' long - flat ceiling

But after 2x checking the span calc I really didn't need it
But figured I would throw it out there