# Calculating the load limits of dimensional lumber and a custom beam

As I build things, how / where can I look up the approximate load values for a “beam” made of dimensional lumber?

E.g.

• What is the max it can hold if it’s in a joist orientation (sideways with the narrow orientation horizontal to the ground).
• What if it’s doubled up and glued?
• What if I put 1/2” plywood in the middle of two and glue it all up?

If you have to pick a wood, I would say #2 Southern Yellow Pine; but I am primarily looking to be taught how to do this vs. having calculations done for me.

I will be building a tree house and I am considering building a loft in my garage.

I understand that the span is significant in these calculations.

• Calculating it - take a side-quest to engineering school. Table lookup is more typical if not. Example for SYP southernpine.com/span-tables Commented Jan 22, 2023 at 19:59
• Usually a rule of thumb for normal floors loads is an inch of depth per foot of open span, a single 2x6 at 16in spacing should span 6ft and be okay. If wanting to place very heavy loads(big safes, hot tubs, masonry fireplaces) having an engineer design joist size is almost/very good sense required. Commented Jan 22, 2023 at 20:23
• Thanks. Both answers are helpful. The documentation @ecnerwal is the sort of thing I was looking for, as some of those tables tell the max load for a given dimensional lumber, or laminated beam.
– Doug
Commented Jan 22, 2023 at 23:51