More foundation questions

[brian_nj]

ok after making a trip to the local lumber yard I am not real impressed with the quality of the 2"x12"20's that are available, So now I am thinking of alternatives. I am not a fan of I-joists (too bounce IMO) so what I am thinking is adding a center beam on the first floor of the 20x30 1.5 story (like the 20' universal plans) with the piers supporting it and using 2x12x10 or x12 depending on the overlap. Then using full span I joists for the second floor (I'll never be up there it is the kids rooms) I do not think that this will affect the load trace from the roof down. I do not plan on using bearing walls as interior partitions on the first floor at all as our floor plan is a bit open for that. Any opinions or critiques would be appreciated.

Brian

[MountainDon]

Sounds like a viable plan Brian. You are just adding a central beam and subbing 2 pces for one for the joists. What you propose would not change any roof down loads.

[brian_nj]

Thanks MountainDon, I thought that was the case but wanted to make sure I was not overlooking something silly. The silly little things always seem to bite me in the end

[John Raabe]

Doing that only lightly loads the centerline beam and only with main floor loads - the center 10' of the floor for a design load of 500 lbs per lineal foot to the beam.

Doing a quick estimate calculation a built-up girder of three DF 2x8's (4.5"x7.25") could carry that load over a span of 8' or less.

[rwanders]

If you don't like bouncy floors, you will indeed be much happier with the center beam----I added a center beam to my 24 wide even though I did use wood I beams at 16"OC---main floor is really flat and rock solid! A few more $$ at the foundation and platform framing stage really pays off IMO long after you have forgotten how much you "saved".

[Don_P]

I might be misreading but your joists for a 10' span shouldn't need to be 2x12's.

[MountainDon]

Might not need to be 2x12, but they offer more insulation space. Could be the reason.     R30 needs 9.5 inches for fiberglass. 2x10 = 9.25, so you could use 2x10's but not have any space for under batt venting if desired.    The 1/4 inch compression does not matter, but shoving R30 into a 2x8 cavity (7.25") reduces the R factor to 25.

Depending on species, grade and spacing 2x8 could be used. But less insulation space.

Insulation recommendations may be found at:

http://www.ornl.gov/sci/roofs+walls/insulation/fig2.html

[brian_nj]

insulation is the main reason we are going with the 12" with 11.5" we still get r-35 even in the areas that we are running supply ducts for the heating and cooling system. The second reason is I can get the 2x12s for the same price so I might as well lol...