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Re: .spanning 22' load bearing wall

From: info@builderswebsource.com
Category: Structural
Remote Name: 63.198.181.43
Date: 01 Feb 2001
Time: 07:34 AM

Comments

To calculate the size of the beam (whether glulam, microlam, or steel), the expected load-bearing weight is required as well as any point loads that are not equally distributed. It sounds like your 13 trusses will equally distribute the roof load. You must account for:

1) Weight of ceiling itself (sheetrock);

2) Tributary load of the portion of roof that will be transferred to the beam (including any new additions);

3) To calculate the roof load, you also need to specify the roofing material, such as tile, slate, composite, shake, etc. as this can make a huge difference on the dead load;

4) Additional weight, such as from snow loads, high winds, etc. (depending on your area).

Once this information is known, the beam size can be estimated. From general experience, however, a 22-foot span will require a relatively deep beam...probably in excess of 12" deep, and likely deeper. For example, in our garage, we have a 24' glulam beam supporting a deck and part of a 2nd story. This member is 6-3/4" x 15" deep, bolted to a 6x6 column on each end with large steel column-beam connectors.

It is possible to set the beam on supporting columns, such that the bottom of the beam is flush with the ceiling. However, depending on the new roof line, this may require that you taper the top side of the beams to match the roof line -- which could weaken the beam if too much is cut. You would use joist hangers to tie the ends of the trusses into the beam.

If you were to use a steel beam, you may be able to get by with less depth vs. a glulam, but this would need to be calculated based on actual loads and anchoring is a little trickier. Builders Websource offers a valuable structural beam design package that lets you calculate various combinations of wood and steel beams given a particular loading condition.

We strongly suggest you contact a local licensed structural engineer to look at your exact field conditions. Running a calculation is easy once the load parameters are known as well as the architectural constraints of your existing structure.

Certainly, by putting in a center support, you'll be able to get by with a shallower beam (since the effective span will go from approximately 22 feet to 11 feet)...but you'll need to be sure you can properly transfer the load to the foundation with proper anchoring.

Good luck!

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