Bob

Hi Bob, I'm no guru on this but I'll guess others will want to know the loading to calculate a deflection on a type of beam to support the weight. The various beams of any given size will have a different cross sections (weigh more per length) and be stronger due to this, so it will all come back to load on the beam and where the load is highest (center, all over, etc.).

I don't know what the load is, but it is currently being held up with a pair of wood 2 by 12's 12 foot long.

Does the beam span 12' or is there intermediate supports? If supported, what is the pitch of the supports (i.e. what is the real clear, unsupported span)?

One thing that needs researching is the possibility of using a glued-laminated engineered timber beam (try Googling 'glue-lam') to replace the rectangular section described. There's all sorts of strange shapes available these days. The building at these co-ordinates has recently used two of them 350 x 175 x 6000mm as the structural supports to provide stability to a Mansard roof. Try getting a single piece of wood to those dimensions!

If this is a ridge beam, then the rest of the peaked roof is a lot lower. I find it har to imagine a peaked roof where an extra 6" head room is needed with no need for more head room in the lower areas??

Please describe better.

Bear in mind you do not usually place steel beams on wooden high places.

There are table of beam stresses online and these should help.

here is one set.

http://www.martindalecenter.com/Calculators4_6_Civ.html