[Roy Rowlett]

:confused1:
I am building a workshop that measures 16 ft across the front and 20 ft deep. The rafters will be front to back (on the 20 ft dimension). I will have a vaulted ceiling , exposed rafters, with no interior walls or posts. I had planned to use wood I-beams, as I did with my floor joists, for the rafters, but I am not sure about the ridge board/beam. I am getting advise from local builders/framers with conflicting information.
Some say I can use my 9 1/2" I-beams for rafters, and a single 2"x12" ridge board across the 16' span at the ridge. Others are saying I need an LVL ridge beam. I have read that a ridge board/beam when used with wood I-joists for rafters should have a ridge board/beam that can support the entire roof load, since the I-beams are not designed to tolerate the compression that can occur in my situation.

Can someone give me a definitive answer to this question:
Can I use a single (or double) 2"x12" board for a ridge board/beam when I use wood I-beams as rafters. They will have a 10-12 pitch across a 20 ft total span (10 ft from front of wall to ridge). ..OR.. could I use a 2"x12" ridge board/beam across the 16' width if I use 2"x8" or 2"x10" dimensional lumber rafters? Both cases will have no interior supporting walls or posts and no ceiling joists. Just supported on the outside walls.
Thanks.

 

[Scuba_Dave]

You won't have any ceiling joists at all?
I went thru this with my walk up attic 17x24
Ridge beam running the 24' length

If I did not have any ceiling joists to hold the wall together then I had to have an engineered ridge beam
That would have been (3) 16" LVL's

 

[Roy Rowlett]

Since my ridge will be about 10 ft above the floor, I could put ties across the cieling area to tie the rafters together.

 

[JohnCarpenter]

If you tie the walls together across the room at least 2 places in the middle, you can use 2x12 butt end to end as ridge. If you leave it completely open in the middle, you must use a single piece ridge, in which case I would use a structural engineered beam. Collar-ties will not help a bit. Without the solid ridge, the weight of the rafters will push the walls apart in the middle.

 

[Gary in WA]

I agree with John C. And the rafter ties need to be 4' on center or 3 total as codes require. Ask your local Building Department as something this big may have issues (zoning, foundation setbacks, electrical permit, etc.). With a permit your Homeowner's Insurance will cover and when you sell it will be listed on the County records as legal. Be safe, G

 

[Roy Rowlett]

What about the wood I-beam vs dimensional 2xs for rafters question?

 

[JohnCarpenter]

If you talking about the I beams made from chip-board glued to a 2x4 on each side, I personally would not use them. I know they are supposed to be so good and structural.

I can just see glue failing in 10 or 20 years where I know a solid piece of wood will still be there. The technology is just not old enough for me to trust yet. Just old fashioned I guess. But, I have never even seen or heard of them them used for rafters.

 

[Scuba_Dave]

I have them as floor joists
Not sure about using them as rafters
They present unique issues as there are limitations on how you can cut them.
But they are used as rafters
Couldn't find a pic where they attach to the wall

 

[Scuba_Dave]

They've been around longer then I thought

An engineered wood joist, more commonly known as an I-joist is a product designed to eliminate many of the problems that occur with using conventional wood joists. Invented in 1969, the I-joist is a man made engineered wood product which has incredible strength in relation to its size and weight. The biggest notable difference, other than their look, compared to dimensional lumber is that the I-joist is designed to carry heavy loads over long distances while using less lumber than a dimensional solid wood joist of a size necessary to do the same task. As of 2005, approximately 50% of all wood light framed floors were framed using I-joists

 

[Gary in WA]

http://www.umass.edu/bmatwt/publications/articles/sizing_engineered_beams_headers.html Span tables at bottom. Be safe, G

 

[SNC]

You can use truss joists (i-beams) as rafters.
Be sure you know about using squash blocks and all. This info should come with the joists. And like someone said the restrictions on cutting them.

 

[Clutchcargo]

Depending on where you live (snow load), you may not be able to use engineered lumber for the ridge board without collar ties or supporting posts.
The ridge and rafters are individual components and are sized independent of each other. Is using engineered trusses out of the question?