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-   -   What size ridge beam do I need? (http://www.diychatroom.com/f19/what-size-ridge-beam-do-i-need-69404/)

madeshotels 04-19-2010 08:07 PM

What size ridge beam do I need?
 
Hi, I am building a 12X24 Storage building in south louisiana and was wondering what size ridge beam I should use. I built my sub floor out of 4x6 all the way around and one 4x6 down the middle and 2x6 between them. I used 3/4" treated tongue and groove plywood on the floors. I have already built my walls out of 2x4 16 OC. I will be putting 1/2" OSB and shingles on roof. My rafters and ceiling joist will be 2x6. Also, would you do 16" OC are 24" OC for the 2x6 rafters? I was told a 2x6 ridge beam would be good enough, but I would like more opinions. Do you think that 2x6 is good enough are what. Any help would be appreciated.

Thanks, Mike

Yoyizit 04-19-2010 08:13 PM

Quote:

Originally Posted by madeshotels (Post 430807)
I was told a 2x6 ridge beam would be good enough, but I would like more opinions. Do you think that 2x6 is good enough are what. Any help would be appreciated.

Thanks, Mike

FWIW,
"Roof ridge beam deflection greater than 25 mm in 2400 mm is considered excessive ."
This is a 1 in ~100 ratio, so Δ/L=5/384 * w[L^3]/EI = .01, so w in pounds/inch distributed load is 0.768EI/[L^3]
L is 24(12) = 240", E assumed to be 1,000,000 PSI, I = [1/12] b[h^3] = [1/12]1.5[5.5^3]= 21 in⁴.
I get 1.2 pounds per linear inch, 290 pounds for the whole ridge beam, dead & live load.

That seems small. Maybe there is an arith error.

Scuba_Dave 04-19-2010 08:18 PM

You only need a ridge beam if you will are not going to have rafter ties
Without rafter ties the ridge beam must be calculated to hold the roof up
If you put in rafter ties you only need a ridge board

Which way is the ridge running ? 6' long rafters or 12' rafters ?
What slope roof ?
I do 16" OC...but we have snow here, I prefer plywood on the roof
Not sure if 1/2" OSB is rated for 24" OC

madeshotels 04-19-2010 08:28 PM

What size ridge beam do I need?
 
It will be 7 foot rafters because I am going with a foot overhang. I decided it was worth the extra little bit to go 16" OC. I'm sorry I did mean Ridge board. My roof will be 6 on 12. The only problem is that I will have to splice it. What size ridge board and for my splice would a 10' 2x6 on each side screwed into the ridge be enough?

Scuba_Dave 04-19-2010 09:01 PM

2x6 rafters use a 2x8 ridge board
I'd go with a 16' 2x8 & add on another 8' for the 24' length
Or if you are going over on each gable end use a 10' 2x8 & cut off the extra
Use splice plates to tie them together

You could get a 24' long 2x8 from a lumber yard, but transporting it home might be a problem

Gary in WA 04-19-2010 10:24 PM

The ridge board is always full depth of cut rafters unless a low pitch(<3/12), then designed as beams. 1x boards "ok", check local code. IRC 802.3 The ridge board can be of any length, splice plates are not required here as it is not structural, only holding the rafters in opposite line.

Be safe, Gary


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