Dealing With Rain in Tents
Water is certainly not quite as much of a hazard to you
and your tent as fire, but it can nonetheless be quite an inconvenience.
For centuries, tent dwellers have struggled with two problems
associated with the interaction of water with their shelter:
rainfall and condensation.
While dealing with the first concern is mainly a matter of closing
off possible entry points and using treated fabric for your tent, the second
concern is somewhat more complicated.
Many modern camping tents come with a rain fly as well
as a factory-administered application of waterproofing chemical, though this
is not necessarily applied to all parts of the tent; just those areas that
are most susceptible to rainfall.
This is typically a polyurethane coating of variable rating in a unit
of measurement known as hydrostatic head, or HH.
It is measured by placing the material beneath a tube and slowly
filling it with water until the water bursts through, at which point the HH
can be measure in milliliters. A
tent should have an HH rating of at least 1500 to be considered waterproof.
Rain fly sheets and ground sheets of tents have HH ratings of up to
5500 and higher.
The factory waterproofing may not be sufficient to
prevent rainfall penetration, particularly as the chemical is prone to
wearing off after a few uses if not applied thoroughly.
It may be a good idea to get some waterproofing of your own and use
it on the ground sheet and the first two feet of the tent walls to ensure
protection.
Condensation is a more troublesome matter, caused by a
combination of heat and breathing.
While you sleep in your tent in the evening, you exhale warm, moist
air, as much as a pint of moisture each night, which creates humidity and
traps water. Sweat and moisture
from rain-soaked clothing add to this humidity, and steadily increase the
threat of condensation forming on the walls of the tent.
Once this occurs, the condensed water vapor will compromise the
otherwise dry tent interior, manifesting as water droplets or as frost
formation in colder climates.
Most tents fight off condensation by incorporating a
twin wall design where the inner layer, or the canopy, is not waterproof,
but the outer one, the rain fly, is, theoretically allowing water to
evaporate through the canopy, then condensing on the rain fly, where the
collected water can either trickle away harmlessly to the ground, or remain
on the rain fly, which will leave one with the problem of drying it, but at
least the tent interior will have remained dry as a result of the system.
Tents also utilize ventilation to allow air to circulate through the tent, keeping humidity and warm air from collecting inside. If the tent is equipped with windows on both sides, they can be opened to allow a breeze to pass through. The door of the tent can be opened if an awning can be placed over the entrance to still protect against rain. The best venting system has both vents at the ground level to allow cool air to enter and vents at the roof level to allow warm, moisture-filled air to escape, but tents are rarely equipped with such a system because it is difficult to likewise shield these tents against rainfall.
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