2 story plan beam question

[phalynx]

John,

Or, anyone who knows.  I am thinking about expanding the 20x34 to 20x40.  By doing so, it would stretch the beam that goes over the living room.  Using the 3 2x12's together, what is the maximum distance I can stretch them before needing a support under them?

thanks,
Scott

[jraabe]

Scott:

If you can get good grade Doug fir (SS or #1) or equal and glue and spike them together to make a 4.5" x 11.25" beam, then my quicky calculation says you can span 14' carrying 350 lbs per LF (assumes a 2nd floor live load of 30 psf - no grand pianos).

You could also use I-joists of course, go wall to wall and eliminate the beam.

NOTE: This is not a professional engineering determination. Just an opinion.

[phalynx]

John,

Thanks for the quick reply and I understand the "disclaimer"..  

So, if I understand correctly, the stock 20x34 plan is really at "practical" maximum span.  Not to open up a HUGE can of worms that I think it may be, how does one calculate the figures you just did?  I was thinking of a span of 18'8" - 20'8".  Would I need a more "engineered" beam or "could" a combination of 3 2x12's together with 2x12x20's as floor joists be enough?  

And, I accept your "opinion" as non binding..    Just looking for "thoughts"

[phalynx]

I think you already answered my question and I just didn't "Get it" until just now.  If I just used I-joists then I wouldn't need to worry about the beam and my guess is the I-joists would be about the same price as the beam + 2x12's.

[Jimmy_Cason]

Because I added 6 feet to my house and built an "L" shaped stair case
the area above my living room has a  beam span of 17'-8"
I have used 3 2x12s with the thought of "feeling it out" when I install to the tongue and groove plywood.
I am prepared to add a decorative support post or beefing it up with another 2x12 added to the existing beam.
Another thought is using 45 degree gusset beams attached to the two supporting columns to reduce the unsupported span.
The area directly above the beam will carry no weight other than foot traffic.
Standing on the beam at this time I get no bounce.
But I am afraid sagging over time might be an issue.

[jraabe]

Yes, the Universal Cottage plan has both full span I-joist floors and standard joists with a beam running down the center. You can use either one (or even mix the floor systems).

My beam calc program allows me to choose a grade of wood, set up a span length, put a load on the beam (determined from the roof or floor above), specify how much deflection I will tolerate, and then set a width for the beam. Then when I hit the Calc button it gives me the required depth of the beam to meet those conditions.

And, as usual, Jimmy C. has some good suggestions. You will likely be fine with the loft loads on the beam you have. You might, over many years, get a bit more deflection than wanted but this is not a safety issue and you would really have to load up the floors to get that.

[phalynx]

We have decided to keep the plans stock now.  The question I have is where the beam connects to the foundation.  In the middle it rests on 6x6's on footings.  On the foundation wall, it says to use a pocket or a hanger.  I am thinking of using a concrete block wall for the foundation.  How would you create a pocket that would allow the beam to rest on the wall without it collecting moisture from the concrete blocks?  Or, what hanger would be used here?

Scott

[glenn-k]

Seems PEG once mentioned putting a piece of asphalt roofing shingle under beams on concrete- Please correct me if I'm wrong, PEG.

[jraabe]

In a poured wall you can put in a piece of foam that you dig out later. It would have at least 2" of bearing and 1" of airspace around the sides of the beam. Then the wood sits on a moisture barrier. This could be 90# felt or an asphalt shingle.

Such a pocket will support the beam and keep it dry. I think I have seen block guys do something similar with broken and 1/2 blocks but don't know the exact trick. I'm sure your local mason could show you.

The other way is by a metal bracket hung inside the wall from the sill plate. These can cost a few $$ but are easy to install.

[Daddymem]

Right or wrong...I looked at a beam under one of the additions on our house and there is a piece of sill seal under the beam sitting on the poured concrete cellar wall.

[jraabe]

Yes, sill sealer would do the job as well.