This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
An important point which must be considered in connection with the framing of the walls and partitions, is the settlement due to the shrinkage of timber as it seasons after being put in place. Timber always shrinks considerably ACROSS the grain, but very little in the direction of the grain; so it is the horizontal members, such as the sills, girts, and joists, which cause trouble, and not the vertical members, such as posts and studding. Every inch of horizontal timber between the foundation wall or interior pier and the plate is sure to contract a certain amount, and as the walls and partitions are supported on these horizontal members, they, too, must settle somewhat. If the exterior and interior walls settle by exactly the same amount, no harm will be done, since the floors and ceilings will remain level and true, as at first; but if they settle unequally, all the levels in the building will be disturbed, and the result will be cracking of the plastering, binding of doors and windows, and a general distortion of the whole frame, a condition which must be avoided if possible.
It is evident that one way to prevent unequal settlement, so far at least as it is due to the shrinkage of the timber, is to make the amount of horizontal timber in the exterior and interior walls equal. Thus, starting at the bottom, we have from the masonry of the foundation wall to the top of the first floor joists in the outside walls 10 inches, or the depth of the joists themselves, since these rest directly on the top of the wall. In the interior, we have, if the joints are framed flush into a girder of equal depth, the same amount, so that here the settlement will be equal. But the studding in the exterior wall rests, not on the top of the joists, but on the top of the 6-inch sill, while the interior studding rests on top of the 10-inch girder. Here is an inequality of 4 inches which must be equalized before the second floor level is reached. If the outer ends of the second-floor joists rest on the top of an 8-inch girt, and the inner ends on a 4-inch partition cap, this equalizes the horizontal timber inside and outside, and the second floor is safe against settlement. The same process of equalization of the horizontal timber may be continued for each floor up to the top of the building, and if this is carefully done it will go far toward preventing the evils resulting from settlement and shrinkage.
With a balloon frame this can not be done, because there are no girts in the outside wall, but only ledger boards which are so fastened that they can not shrink, while in the interior walls we have still the partition caps. All that can be done in this case, is to make the depth of the sills and interior girders as nearly equal as possible, and to make the partition caps as shallow as will be consistent with safety.