TM 5-852-9/AFR 88-19, Vol. IX
(b) A special enclosed heated crawl space immediately below the ground floor elevation may
be provided in arctic building design. Its floor can be constructed with removable insulated panels. All piping,
including hot and cold water, heating lines, and waste piping, can be run in this space. The area must be
tightly sealed to avoid air infiltration. This system has several benefits: piping is readily accessible for
maintenance; it can be replaced easily; and the space provides a buffer zone to warm the floor above.
(2) Disposal of roof and floor drainage. Drainage from roof and floor drains should not be piped
to the sewage system since this would increase sewage treatment requirements. This drainage must be
disposed of separately. As discussed in (b) below, an exception is allowed. Although no perfect disposal
method has been developed for all situations, several usable systems are presented below.
(a) Dry wells are underground manmade cavities below the seasonal frost level. They can be
constructed by burying concrete pipes, concrete rings, or pockets of large stones or gravel capable of holding
large volumes of water. Dry well use is limited to subarctic areas with free draining soil free of permafrost.
If wells or connecting drains freeze, they will back up water toward the roof and create leaks within the
building. Silt, leaves, and other foreign materials deposited on roofs are carried through the strainers into the
roof drain system. This material seals off dry wells so that no leaching occurs after a few years. Oil can also
seal off drainage in dry wells. Dry wells which become inoperative must then be replaced with new wells.
(b) Roof drain lines which discharge through an exterior wall onto a splash block cause
glaciation. When this glaciation occurs on paved vehicular or aircraft traffic areas, one solution is to use a
concrete trench with a grate cover to move water and glaciation away from the area. Frequently the exterior
wall outlets freeze solid, backing up water in the rain leader. For this reason, an overflow line from the rain
leader is connected to the sanitary sewer inside the building to allow the back up water to escape. Usually
cyclic freezing occurs in the outlet during breakup conditions. Overflow drains are not included in the
building waste water fixtures unit calculations.
(c) Floor or trench drains in shops collect considerable mud, gravel, sticks, and vegetation
brought in by tracked and wheeled vehicles. Baskets, strainers, and sand and oil traps must be provided to
keep these drains operational. Drains, traps, and underfloor piping are difficult and costly to install and
maintain, but floor and trench drains are generally essential to carry away melted snow carried in by vehicles.
(3) Roof drains. Exterior roof drains may be damaged by snow and ice accumulation. When
required, roof drains should be a minimum 4 inches in diameter to reduce probability of closure by ice and
frost. Interior roof drains should be provided or roof drains should be eliminated and the roofs sloped to the
eaves.
(4) Roof vents. In subarctic regions, vent pipes should be increased one pipe size to prevent complete
frost closure. The minimum vent size should be 3 inches as required by TM 5-810-5. In true arctic areas,
vents should be insulated along their full length to their termination above the roof.
(5) Installation of plumbing vents. In high snowfall areas, plumbing vents on gable-type metal roofs
with cold attics should be installed near the roof ridge or should be reinforced to withstand snow and ice
loads. Figure 4-9 shows snow accumulation on a roof of this type in a subarctic area. Snow or ice slides may
break off vents and other projections.
(6) Heating grease and oil traps. If the water in grease and oil traps freezes, the traps will become
inoperative. Heating is required to keep these traps operational. These traps may be installed inside the
building to prevent freezing.
(7) Use of lightweight material. Lightweight materials should be considered when air transportation
to the site is required. Materials to reduce installation costs, such as copper or plastic piping, should also be
considered. Current guide specifications should be checked for restrictions on the use of plastic pipe which
must be able to withstand extremely low temperatures. There must be adequate design considerations for
plastic's higher coefficient of expansion. Pressed steel or lightweight fiberglass plumbing fixtures are available
and are more suitable for transport by air than the heavier cast iron fixtures. Such materials, however, must
meet minimum operational requirements.
(8) Garbage disposals. At small, remote installations where sewage treatment and disposal are
particularly difficult, garbage disposals are generally not installed. If disposals are installed, grease removal
must be considered. Grease may congeal and clog cold sewer lines, and may also create operation and
maintenance problems at the sewage treatment facility. Oversized exterior grease traps have been used to
remove grease, but frequent cleaning is required. The normal foodstuffs run through a garbage disposal also
have a tendency to reduce the life of a septic system drain field or leach pit.
4-15
Previous Page
