Cork insulation; a complete illustrated textbook on cork insulation ...

STRUCTURAL SUGGESTIONS 209
appear that in the manufacturing process all voids, especially
surface voids, cannot be eliminated. Thus water in contact,
as just explained, has been knov^-n to penetrate corkboard
<strong>insulation</strong> to a depth of an inch or so toward the outside
building M'alls.
Water may also find its way into corkboard <strong>insulation</strong>
through an entirely different source, that is, from the outside
of the building. When the temperature of a cold storage
room is lowered by refrigeration, the air in that room contracts
with cooling, because cold air occupies less space than the
same original volume of warm air. Thus the cooling of the
air in a cold storage room creates in that room a temporary
partial vacuum, or an unequal pressure between the inside
and the outside of the room. If the room is tightly closed,
air will be sucked through the building walls and the insula-
tion, to balance the unequal pressures, and this air, carrying
with it water in suspension, the quantity measurable by the
humidity of the air, wuU precipitate its moisture in the insu-
lated wall where the dew point is reached.
The discovery of these two distinct ways in which moist-
ure is placed in corkboard <strong>insulation</strong> has been of great value
in revising <strong>insulation</strong> specifications. The air-proofing of the
surfaces to which the <strong>insulation</strong> of cold storage rooms is
applied, to be carried out as best as possible under each set
of conditions, is now done wherever possible or feasible, so
that instead of air being drawn through the building walls
and the <strong>insulation</strong> to compensate a partial vacuum, such air
will be supplied through some other channel or in some other
way. For example, it is now frequently the practice in large
ice storage houses to install a small air compensating vent
door or opening in or near the ceiling.
It will be noted that surfaces to receive <strong>insulation</strong> are
recommended to be air-proofed, not water-proofed ; and the
necessity for air-proofing is believed to increase with decrease
of cold storage room operating temperature, and in a general
way with the size of the room, that is, the greater the cubical
content of the room the greater will be the vacuum effect
produced by the refrigeration. Again, the choice of the kind
of materials used in the building construction, for instance,
will decrease or increase the resistance of the passage of air.