"scabbing" structural members 2x8 doug fir rough 1

[remington7]

Greetings, I have a project involving a shed style roof with a 20' span. The material is rough sawn douglas fir 2x8, and 2x10. The problem is the length of the new material is generally 16', is there a best practices proffessional approach to building members that will span 20', and leave overhang, so a total rafter length of about 23'. Inspector frowned on country style scab of approximately 6' nailed on both sides of the joint. Now what? PS. we can do this with truck frames and the scab area is stronger than the non-scabbed .Thoughts on correct rafter spacing also appreciated.

 

[msquared48]

If you use microlams or PSL's there won't be a length problem.

You may be able to get 24 footers on a special order though if required.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[DaveAtkins]

You can certainly scab members together, IF you properly engineer the connection. It will take many lag screws, because the connection must be designed for shear and moment.

DaveAtkins

 

[dicksewerrat]

First, it is real hard to weld wood. Second, is this wood that the boss found near a sawmill? Are they really douglas fir? Why not just buy the right trusses for the job? Shrink the bldg?

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[remington7]

Thanks Guys, yes we have the wood from a supplier of such rarities as douglas fir. The building already exists, and this is a new roof structure with a 4/12 pitch. We built kne wall extensions and raised the roof to get this new pitch. The trick is to do this on a tight budget if possible and hopefully fasten some shorter members together with enough integrity to exceed the strength of a single contigous member of 2x8" nominal. Possibly sandwitching plywood for the entire length and constructing a "header" style member will suffice with lag bolts or through bolted carriage bolts? I have pulled truck engines with such members in the barn back home.

 

[dhengr]

You would do well to stick to pulling engines in the barn back home, just don’t stand under them when doing this. Get a structural engineer to size and space these rafters properly, and then buy them the correct length, they are available. Small trusses or I joists would work too. This will do more for your tight budget than a whole bunch of sandwiching, drilling and bolting which an engineer must design also. And, it will work a good deal better and look better too, knee walls or not.

 

[Brad805]

I would be cautious using rough sawn lumber. Technically, it does not comply with most building codes since it is usually not professionally graded.

Brad

 

[remington7]

Thanks Brad, this lumber is graded, and we have a grade letter aproved by inspector.

 

[dhengr]

Then you have everything you need except long enough rafters, loading and spacing criteria and a structural engineer who will design the rafters and the splice and sign off on it to satisfy the inspector; not small items to fulfill.

The splice will extend about to the max. bending moment point on the rafter, and a 20' span is really pretty long for 2x8's or 2x10's whatever the loading. We buy 16' long 2x8's ~$8.75 & 2x10's~$11.50; and 24' long 2x8's~$19.75 & 2x10's~$24.75 & 2x12's~$29.30, at a big box store, and depending on grade they will be higher. But, 2(11.50, 2x10's)=$23.00, plus six or eight bolts, drilling and fit-up, labor time and experience, etc. etc.; you get real close to $29.30, 2x12's which might start to get you a proper roof system on that span. Sometimes free material is better saved for another project than used in an improper fashion.