Live loads

Building loads are traditionally divided into two large groups: Dead loads, which act for the entire life of the building, and Live loads, which act for a shorter period of time.

Roof and walls - snow, rain, ice, wind and earthquake loads, may only last for seconds.

Inside floors - weights of people, furniture, moveable equipment, considered to be in place for 10 years.

Live loads are mandated by the building code. But note, that with a changing climate, building code minimums may not be sufficient.

Building use, gravity loads only

Roof live load, from construction workers and materials.
Occupancy loads, from people, furnishings, vehicles, equipment, storage.

Some minimum live load examples:

Dwelling living areas: 40 psf
Dwelling: bedrooms: 30 psf

Attic (no possible storage): 10 psf
Attic (no possible rooms): 20 psf
Attic (future rooms): 30 psf

Offices: 50 psf
First floor stores: 100 psf
Places of assembly: 100 psf

Natural forces, including gravity, pressure, earthquake loads

Including:

Snow load: weight of snow, ice and rain-on-snow surcharge.
Rain load, including ponding on flat roofs.
Wind pressure from maximum 3-second gusts.
Earthquake, vertical and horizontal movements.
Ground water pressure.
Lateral earth pressure.
Expansion and contraction stress.

Some useful but very approximate reference values:

Snow weighs about 20 pounds per cubic foot.
Ground snow load in the US varies from 0 to more than 100 psf.

Minimum roof load for maintenance: 12 to 20 psf

Design wind speeds (3-second gust) vary in the US from 85 to 150 mph.
For most of the US, 90 mph: -15 psf uplift to 15 psf pressure.
Along the coast, at 125 mph: -30 psf uplift to 30 psf pressure.
Along the coast, at 150 mph: -60 psf uplift to 60 psf pressure.
Add 50% for eaves, corners and overhangs.

WOOD BEAM SIZINGTM Live loads

Building use, gravity loads only

Natural forces, including gravity, pressure, earthquake loads