Ridge 'board'/'beam' for slope less than 3:12, without PE (California)

[Keith]

For a small residential addition in which the existing roof slope is 2:12 the ridge span is only 13' and rafter lengths 11'-4".

Since R802.3 2010 CRC states that for slopes less than 3:12, ridges, hips and valleys shall be designed as beams.

If the new roof is california framed on top of the existing roof, do i still have to engineer/provide beams for the valleys?

Can the new rafters be tied to the existing perpendicular rafters?

Regarding the ridge beam, in a previous similar project for a 2:12 slope roof, the plan check engineer allowed me to simply provide a post, cutting the span of the ridge in half (to a 12'-0" span) and let me use a dbl 2x8 for the ridge WITHOUT ANY ENGINEERING.

I felt pretty lucky.

I know this enters dangerous territory where a credentialed engineer may have been denied their compensation for the benefit of the client; as a result of a sympathetic plan check engineer ignoring the liability of the agency they work for.

That issue aside, is there any exception to R802.3 info above based on a limited span of the ridge for a 2:12 slope roof?

Any where I can go to size the ridge and cross my fingers that the design is approved without a stamp?

Thanks.

 

[Francis Vineyard]

Just had a contractor come in yesterday with calculations done and shown from posting his question on an engineer forum to span 6x6 24 oc floor joist. So yes, but will the AHJ accept it?

 

[steveray]

would they let you use "eng" LVL type product with no stamp that can be verified through manuf data?

 

[DRP]

I had wondered if they called that california framing out there.

Actually you can get a stamped design for the ridge from the LVL supplier, it will only cover the beam.

If the existing rafters have the capacity to take another dead load then the valley wouldn't worry me in your climate, but I'm just a carpenter.

awc.org has DA6 Beam Design Formulas in it's free download library, look at case #18.

If the ridge were sized as a "uniformly loaded beam overhanging one support" it would be conservative, the load on the overhanging end towards the valley has a decreasing load to the end.

This is those formulas written into a javascript.

http://www.timbertoolbox.com/Calcs/ohangunild.htm

 

[jar546]

I think we need some California inspectors to jump in here so I am going to edit the name of the thread to help. I do not have in my possession a CA building code.

 

[Keith]

would they let you use "eng" LVL type product with no stamp that can be verified through manuf data?

Although some city/government agencies might accept verification through manuf data, I don't expect this one to not only due to liability but also their support for the profession in which a stamp is required.

Is there a CRC table I can use to do a shed roof? (regardless of slope).

Is the floor joist table my best bet or are there any other options?

http://ftp.resource.org/codes.gov/bsc.ca.gov/gov.ca.bsc.2010.02.5.html#p431

 

[DRP]

Do you not have the rafter tables in chapter 8?

 

[Keith]

Do you not have the rafter tables in chapter 8?

Aren't those rafter tables specific to only a ridged roof of 3:12 or more with clg joists attached?

 

[DRP]

Not unless you have a cite to make a liar out of me.

The rafter tables are set up with the rafter as a uniformly loaded simple beam. The "rafter" (a beam by any other name) could be dead level and support the given load. The floor joist tables would work but would give a conservative span under most conditions as they do not typically factor in the same duration of load.

 

[mark handler]

Even though what is described can be "california framing" the bearing members maybe overstressed and should be looked at by a design professional(architect or engineer).