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Engus 04-13-2009 07:56 PM

Horizontal spans
 
I'm going to be building a 4/12 pitch gable porch roof over an existing 18'x8' concrete pad this Spring.
The new roof will be built at a right angle into an existing 5/12 pitch roof and extend out 8 feet.
My question is this :
Can I get by with 3 posts, 9 ft apart on the out edge of the porch using double 2x6's with plywood spacer headers or will I need to use 2x8's with
plywood spacers ?

I am not going to be using trusses, and will be building
the roof using rafters. Can they be 2x4's with a 1x6 ridge board or should I use 2x6's with a 1x8 ridge board ?

Thanks!
Steve.

joel v. 04-13-2009 09:26 PM

If I'm reading this right your wanting to build a lean to.Correct? A span calculator says that 2x6 at 16"o.c. is plenty. For headers I would do a double 2x8 or a triple 2x6 but likely the double 2x8. Nail them together with lots of nails.

Gary in WA 04-13-2009 11:34 PM

What is the spacing? What is the species? Elbow braces for shear? Post caps and bases? Any snow load? Location? Be safe, GBR
Species1 Compression perpendicular to grain design value, psi. (Fcperp) Douglas Fir-Larch 625 Eastern White Pine 350 Hem-Fir 405 Southern Pine, Dense 660 Southern Pine, Select Structural No.1, No.2, No.3, Stud, Construction, Standard, Utility 565 Southern Pine, Non-Dense 480 Spruce-Pine-Fir 425 Spruce-Pine-Fir (south) 335 1. Design values apply to all grades for the species listed unless otherwise indicated in the table above. EXCERPTED FROM SPAN TABLES FOR JOISTS AND RAFTERS, Copyright 1993 AMERICAN FOREST & PAPER ASSN., WASHINGTON, D.C.

Engus 04-14-2009 06:56 AM

No, Joel.
As stated, it will be a 4/12 pitch gable end roof.
At right angle to existing 5/12 gable end roof.

Gbar,
Standard studs are #1 grade select southern pine, the type that is available in Lowe's and Home Depot here in Northern Virginia.

The question I'm asking is basically this:
On the outward end of the gable roof, a span of approx. 18 feet, I intend to use three 4x4's inside vinyl sleeves for support.
Therefore, the spacing between posts would be in the area of 9 feet.
[post]-----9 foot run-----[post]-----9 foot run-----[post]

Coming away from the existing roof, I intend to set the beams inside the boxing on top of the existing walls for
support, and they will be coming out 8 foot.

[new gable end roof 19 foot run]
[post]---------------------[post]------------------[post]
| |
| 8
| ft.
| length
| |
| |
| |
| |
---------------[ existing roof ] ----------------------------

I hope the diagram makes sense.

Are double 2x6's with half inch plywood spacers sufficient, or would you go with 2x8's with half inch spacers?

Gary in WA 04-15-2009 09:40 PM

The 18' gable goes 8' back to the house and ties in on that 5/12 slope, right? I'd use 2-2x8's under the gable. And if 24"o.c., 2x6 rafters with no snow load, span 11'8". And use 2x6 collar ties or ceiling joists as per table.

http://www.colonie.org/forms/building/bdspanab.pdf That chart is for NY, and 50# snow load. The chart I have says 30# snow load per square foot, and 2-2x10's span 8'5". Check with your local Building Department for the local snow loads incurred. Be safe, GBAR

Engus 04-16-2009 07:18 PM

Yep, Gbar, you are spot on.
A friend gave me the local code sheet (Virginia area), but
I have the tendency to overdue rather than chance things.

The codes show that the gable end can span 12 feet with double 2x6 beam/24" OC, and 16 feet with 2x8's/24" OC, so since I have only 9 feet span between my three posts, I would think I'd be OK with double 2x6 beams.

For rafters on a 4/12 slope, 2x6 can run 14' 8"/16" OC ,
12' 2"/24" OC .

I'm planning on 24" OC with 2x6 collars and will also put in braces and purlins with 2x6 joists.
I'm also figuring on using tie straps on the rafters.


One last question, If I may:
How would you recommend connecting the 8 foot beams to the 18 foot beams at that outside corners that will be sitting on the posts ?
Sit the 18 foot beam on top of the post and end nail the 8 foot beams to it ?

Thanks for your replies. I appreciate it.


Gary in WA 04-16-2009 08:10 PM

I would use a 24" flat strap, bent L - shaped to tie the two off, with an LCE or similar to connect to the post.

http://www.strongtie.com/products/Ca...?source=topnav

Be safe, GBAR

joel v. 04-16-2009 09:32 PM

I understand what you mean now but GBAR has it answered now. I had a vision of a lean-to for some reason.


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