The live load is variable, and consists of the weight of people, furniture, stocks of goods, machinery, etc. The amount of this load, which should be added to the dead load, depends upon the use to which the building is to be put. Where the floor is required to support a considerable live load, concentrated at a particular place, such as a heavy safe or piece of machinery, special provision should be made in the floor construction for it. Table V gives the live loads per square foot recommended as good practice in conservative building construction.

Table V

Live Loads.

Lb. per Sq. Ft.

Dwellings, offices, hotels, and apartment houses ............................

From 40 to 70

Theaters, churches, ballrooms, and drill halls...................................

From 80 to 120


From 150 up


From 150 to 250

A live load of 70 lb. per sq. ft. will seldom be attained in dwellings; but, as city houses are liable to be used for other than dwelling purposes, it is not generally advisable to use a lighter load. In country houses, hotels, etc., where economy demands it, and the intended use for a long time is certain, a live load of 40 lb. per sq. ft. of floor surface is ample for all rooms not used for public assembly. For such rooms, a live load of 80 lb. per sq. ft. will usually be sufficient, as experience shows that a floor cannot be crowded more than this. If the desks and chairs are fixed, as in a schoolroom or church, a live load over 40 to 50 lb. will never be attained.

Office-building floors have been designed for a live load ranging from 20 to 150 lb. per sq. ft., but a conservative practice is to use about 70 lb. per sq. ft. An investigation of the live loads in over 200 office buildings in Boston showed that the greatest live load in any office was 40 lb. per sq. ft., while the 10 heaviest loaded offices averaged 33 lb. per sq. ft., the average live load for the entire number of offices being about 17 lb. per sq. ft.

Retail stores should have floors proportioned for a live load of 100 lb. and upwards; while, for wholesale stores machine shops, etc., a live load of at least 150 lb. per sq. ft. should be figured on. The static load in factories seldom exceeds 40 to 50 lb. per sq. ft. of floor surface, and usually a live load of 100 lb., including the effect of vibrations due to moving machinery, is ample. The conservative rule is general, to assume loads not less than the above, and to be sure that the beams are proportioned to avoid excessive deflection. Stiffness is a factor as important as mere strength.

In designing the floors of office or buildings of like character, it is good practice to figure the full live load on the floor joists or beams, but to consider only a certain percentage as coming upon the girders, columns, and foundations, on the assumption that all of the floors will not be fully loaded at the same time. This percentage should be carefully considered in each case; and the amounts will depend upon the height of the building in question and the judgment of the designer.

In proportioning the foundations of hotels, office buildings, etc., the live load may be neglected, but should be considered in heavy warehouses. In buildings carrying heavy machinery causing much vibration, it is good practice to double the estimated live load.