Need a metal beam to span 18' for my outside deck. What size & type beam can I use? The loading is 40lbs live & 10 lbs dead.

Where do you plan on getting the beam? Many suppliers will size it for you.

Why do u need steel? Why not wood?

Chuck

The span is to long for wood & an engineered lumber beam is not designed for weather exposure

Tugger

Depending on your location you will/may need a building permit. To get a building permit you will have to submit drawings of what you want to do. The building dept may require architectural drawings from a certified architect and/or load bearing report from a construction engineer.

Check with building dept to find out what you need to apply.

Chuck