This section is from the book "Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc.", by George Francis Atkinson. Also available from Amazon: Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc..
The beds are usually arranged in tiers, one above the other, though in some houses the beds are confined only to the floor space. Where they are arranged in tiers in a house of the proportions given above, there are three tiers of beds. There is one tier on either side, and a tier through the middle; the middle tier, on account of the peak of the roof at this point, has one more bed than the tiers on the side. The number of beds in a tier will depend on the height of the house. Usually the house is constructed of a height which permits three beds in the side tier and four in the center tier, with an alley on either side of the center tier of beds, giving communication to all. If the house is very long and it is desirable, for convenience in passing from one house to another, to have cross alley-ways, they can be arranged, but the fewer cross alleys the larger surface area there is for beds. The size of the beds is governed by convenience in making the beds and handling the crop. The beds on the side tiers, therefore, are often three to three and one-half feet in width, affording a convenient reaching distance from the alley. The beds of the center tier have access from the alley on either side and are usually seven feet in width. The width of the alley varies according to the mind of the owner, from two to three or three and one-half feet. The narrow alley economizes space in the structure of a house; the wide alley, while slightly increasing the cost of the structure, makes it much more convenient in handling the material, and in moving about the house. The beds are constructed of one-inch boards. Various kinds of lumber are used, the hemlock spruce, the oak, Georgia pine, and so on. The beds are supported on framework constructed of upright scantling and cross stringers upon which the bottom boards are laid. These occur at intervals of three to four feet. The board on the side of each bed is 10 to 12 inches in width. The bottom bed, of course, is made on the ground. The upper beds in the tier are situated so that the distance is about three feet from the bottom of one bed to the bottom of the next above. Figs. 228 to 231 show the general structure of the beds.
View in mushroom house (Wm. Swayne), showing upper bed in left hand tier. Copyright.
One portion of the house is set apart for the boiler room, where a small hot water heater is located. The position of the heater in one of these houses is shown in Fig. 227. In other cases, where the plant is quite a large one, a small separate or connecting boiler apartment is often constructed. In other cases, where the house is connected with or adjoining a system of greenhouses devoted to hothouse vegetables, the water pipes may run from the general boiler house which supplies the heat for all the houses. The water pipes in the mushroom houses are sometimes run beneath the boards or the walk in the alley, or in other cases are run just beneath the roof of the building.