I am working on a early '80's Salt Box style home with exposed rough-sawn cedar beams. It is a small 1-1/2 story home (1100 sq. ft) that is 15 ft. wide over a crawl space. The ceiling joists are 2x8s.

I want to replace the rough-sawn cedar ceiling beams on the first level using double (or triple) 2x8s and joist hangers placed into the ceiling. The longest beam span will be 12'; longest joist span is also 12'. I will build temp. support walls, pour two footings, where needed, replace the support studs for the beams, etc.

My concern is the use of 2x8s. Should I use LVL or PVL for beams, or are multiple 2x8s robust enough for the beams?

you do not explain why your doing this.
Are you planning to make another floor level above? What are you supporting? Or better yet what are the cedar beams supporting?
Not having any of this information no one can give you any advice.
Please be more specific about what your attempting to do and what exists now.

The size of the home will stay in tact- no room additions or additional floors. The 4x12 cedar beams, placed at 1/3 intervals, are supporting the upper floor. One beam in the hallway is 4' long; the other, in the living room, is 15' long. The home has 8' ceilings, and since the beams are 12", they visually restrict the openness. Relocating the beams into the ceiling will create a more open appearance without delineating the space, giving a smoother transition from room to room, so to speak.

Still not enough info.

What floor is the beams supporting?
The first floor?
Are these ceiling joists supporting the floor of the attic?
When you say they ar at 1/3 intervals. How far are they apart?
How many are there?
What exactly are you trying to acheive?
Do you want to hide these support structures so you have a more open ceiling?

My understanding is that these beams are the support for the flooring of what ever room(s) above. If this is an attic the job would be to determine what loads are the flooring above supporting?
This is a difficult a task to hide beams, and very time consuming as you need to support all floor joists while you remove the existing beams and replace them with something to support the joists that will be buried into the ceiling.
You need to determine if the beams are holding the exterior walls from pushing out as they are a structural part of the home.

My best advice would be to contact a professional engineer to determine load profiles, and sizing of these critical support boards. There are simply way to many variables to answer this type of question on this without seeing the task at hand.

Besides you WILL need to get the local township approvals (permits) to do such a task.
Not doing so will put your home owners insurance at risk should a failure take place and no permits were issued.

If you want a flush ceiling, you're probably looking at steel and not wood for some of those spans. Take a clue from the existing beams which are 12 inches deep. That depth is what will be required with any other form of sawn lumber. Maybe LVLs will give you a little less depth. But I agree with HCC, you will need a qualified design professional to evaluate the loads and design the beams, and I also agree that recessing a beam into a ceiling is not easy. It's important to check the new beams for deflection as well as load-carrying ability.

quote:

Replacing a beam

First, you need to know what kind of wood, then determine the strength characteristics. After you know what it is, the easiest thing to do is determine your replacement structural member of equivalent or preferably stronger. Chances are, you will need a rather huge beam to support the load without the 10' support spans. You also need to know the estimated deflections of the original beam as you don't want sagging in the middle. Removing the 10" support beams sounds aggresive

Then the real engineering starts. You are going to need a solid plan on how to replace this beam. Clearly, this beam supports a lot of load. I would realy like to see you come back to this forum and ask more questions.

I would get a local engineer (PE) involved to verify all calculations, replacment material, and review the plan to replace the existing beam.

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