In addition to stairways, towers are placed at the rear of the mill,
for the purpose of accommodating the elevators and sanitary
arrangements. It is not desirable that elevators should be boxed or
surrounded with anything that would result in the construction of a
flue; but it is preferable that they pass directly through the floors,
with the openings protected by automatic hatchways which close
whenever the elevator car is absent. In the washroom, etc., in these
towers, it is desirable to protect the wood floors by means of a thin
layer of asphalt.