When the attic space is accessible the author usually adds from 3 to 5 pounds per square foot for occasional loads on the ceiling, such as persons walking or climbing over it, or for the storage of odds and ends.
When a floor is supported by the truss, the dead weight of the floor should be computed, the same as for a ceiling, and if there are any partitions these must not be overlooked. Four-inch stud partitions, plastered both sides, weigh about 20 lbs. per square foot. An allowance must also be made for live load on the floor. If the floor is to be used for sleeping or living rooms, an allowance of 40 lbs. per square foot for live load will be ample. For committee rooms, etc., allow 75 lbs. per square foot, and for assembly rooms and dancing not less than 120 lbs. If used for storage of any kind, an estimate should be made of the probable maximum load that the special class of goods will give. Data for this purpose may be found in Chapter XXI. of the Architect's and Builder's Pocket Book.
For certain types of trusses the live floor load may be considered as a dead load, while for other types the stresses should be computed both with and without the live load. This subject is more fully considered in Chapter VIII (Architectural Terra Cotta).
To the weight of the roof construction proper should be added an allowance for the weight of the trusses. If trusses could be built in exact accordance with the theoretical requirements their weight would be directly proportional to the roof load and span, but as there is always some extra material, it is impossible to determine the weight of any proposed truss exactly until it is completely designed. Several tables for the weight of wooden trusses and formulas for steel trusses have been published, but hardly any two of them are alike.*