## Structural Ridge Beam Design Help

Started by Starvin, December 07, 2016, 12:53:15 PM

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#### Starvin

Hey all!

I am looking for a little help in designing a structural ridge beam for my cabin.

CABIN SPECS:
- 12x18 (thus, the ridgebeam would span 18')
- 12x8 loft
- ~2' knee-walls @ loft
- 12/12 pitch roof
- Plan to use metal roofing
- My town does NOT have a building inspector or required code
- I plan to use rough-sawn eastern white pine, sourced on-site

Here is a rough SketchUp screen capture of what I am envisioning. I want to design a structural ridge beam to avoid collar ties (which would lose head room in loft), or a post in the middle of the cabin to support the ridge beam span mid-way (this wouldn't be the worst thing in the world, but would like to avoid the "awkward" post).

- Ground Snow Load for my Town = 90psf

- Roof Live Load = 14psf (this is a guestimate based on some charts I found online).

SO.....
I am fuzzy on what to do next? I am trying to determine if I can get away with doubled-up 2x10 ROUGH SAWN eastern white pine for the ridge beam? Is this possible? If not, would doubled-up 2x12's work? Or am I destined for an LVL?

All help appreciated! Thanks!

#### Don_P

White pine, NO!
Here's my beam calc;
http://www.timbertoolbox.com/Calcs/beamcalc.htm
The area is 6' x 18'... I multiply that by (the ground snow load + dead load). That is the total load to be entered.
Fb for EWP is 575, for LVL 2800-3000
E for EWP is 1.1, for LVL 2.0
Fv for EWP is 135, for LVL 280

I'd use a double 14" LVL.

#### Starvin

Thanks for the help Don, but I am hoping you can dumb it down for me?

I'm not certain how to use that calculator you linked to. The calculators I've seen output beam dimensions based on the entered stats. This does not appear to do that?

Also, why wouldn't you be adjusting the Ground Snow Load to a Roof Snow Load? I would think that with a 12/12 pitch roof, the adjusted snow load on the roof would be drastically reduced from the ground snow load. Using the pure Ground Snow Load would seemingly result in an extremely overbuilt beam? No?

Again, I greatly appreciate the help. I don't mean to challenge your intellect, I just like to try to fully wrap my head around things and push back on things that aren't immediately intuitive to me. Thanks in advance for your patience!

#### Don_P

My calc uses the equations behind the codebook tables. I simply took the math and wrote it into javascript so I wouldn't make dumb math errors. You are entering load, span, beam dimensions and strength of the material and it checks whether the beam is sufficient.

I've seen snow and people do funny things so I design stout. I've had 3' of consolidated snow and ice stick to a 12/12 simple gable before. I've also had folks realize it might be better to hold the snow up there than let is crash off.  Think it through before taking reductions.

Long day, redirect if I missed the mark.