Beam Size If Attic Above
Fine homebuilding notes that 2 inch by 6 inch garage joists will support a weight of up to 50 pounds per square foot.
Beam size if attic above. These nine beam spans are for built up beams made up of either 2x8 2x10 or 2x12 dimensional lumber nailed together as either 3 4 or 5 ply beams. Window door garage door headers supporting roof wall floor loads. The idea behind sizing headers and beams is straight forward. Window door garage door headers supporting roof loads only.
The formula for the section modulus is beam width times beam depth squared divided by 6. The job of headers and beams is a simple one. Two 2 by 4 beams together would not be enough. They transfer loads from above to the foundation below through a network of structural elements.
A 2 by 8 beam would be sufficient. Anything 5 and above we always at least double cripple. Although you can construct a garage using thicker stronger joists 2 inch by 6 inch joists are sufficient for most garages even if you intend to build an attic storage area above your garage. Add together all live loads and dead loads that act on the member and then choose a material that will resist the load.
Tables providing size selections for various beam spans and loading combinations for southern pine dimension lumber and southern pine glued laminated timber are available for the following applications. For example a 3 ply 2x8 beam would use three 2x8s nailed together side by side. On longer spans the beam may require much more bearing space as indicated by this table.