Expert: Daniel Humphrey - 1/21/2008

Question
I am finishing my basement.  I have a support column in the middle of the room I would like to remove.  The column is between the foundation and another column the total distance is 12'6".  The support beam looks like a prefab beam 4"x 12" and the columns are cement and steal.  This holds up 1/3 of the house.  (Family room and living room on the 1st floor and master bed and bath on the second and attic space.

What types of support beams and columns can I put in to replace the center column?

Are there any trpes of beams and supports made for long spans?

Is there a formula to figure out the weight load of a support beaam and column?

I thanks you in advance for your time and expertise.

Gabe

Answer
Gabe,

I'm not sure of your span, once you take out the post. A distance of 12'-6" is an easy distance to span in a two-story residence, but a 25' span is much more difficult for a support beam. It's not just that you need to hold up the floor and keep it from deflecting, you need to keep the bounce out as well.

For loads in the range you have, a wooden post of about 8" x 8" dimensions would handle that easily. Wood has tremendous compressive strength in the long direction, as long as it doesn't bow out. Posts are easy.

But as far as wooden support beams go,  25 feet is stretching it for anything but a deep glue-lam (over 12" deep and 8" wide). I'm just guessing at the loads here; only a detailed analysis of the upper structure could give you a real weight figure to go by. Since there are different formulas for different materials that the beams are made of, you would need to get those from the manufacturer. For common softwood beams, Western Wood Products Association has good strength tables. (http://www2.wwpa.org)

You also may have the option of going to a steel beam and wrapping it in sheetrock for fire code. (Steel loses its spanning ability when heated.)

For people thinking of removing a post like this (especially if we're talking about a span of 25 feet), I recommend having a builder or engineer come take a look.

I'll be glad to look at this project more closely if you want to give a more thorough description of the actual span without the offending post, the floor structure, the uses for the rooms above, and the walls directly above. You might also tell me what kind of headroom you have and what kind of treatment you would give a beam down there.

Dan