In most climate zones, conditioned unvented crawlspaces perform better than vented crawlspaces in terms of safety, health, comfort, durability, and energy consumption. Research has demonstrated that these conditioned crawlspaces also do not cost more than vented crawlspaces. Crawlspace venting is a widely accepted business practice across the country. However, in humid climates, the warm, moist air entering the crawlspace is more likely to condense on crawlspace framing than to help dry out the crawlspace. This is because the outside air often has a dew point higher than the interior crawlspace framing surface temperature. As evidence, existing vented crawlspaces have experienced severe moisture and mold problems costing builders and homeowners significant resources to repair.

Unvented Crawlspace

Unvented Crawlspace

The housing industry has been reluctant to use unvented crawlspaces despite their compelling benefits and the history of problems with existing vented crawlspaces. One of the reasons commonly cited by builders and designers is “the code does not allow me to build unvented crawlspaces.” This is both generally correct and misleading. The model codes do not allow the construction of “unvented” crawlspaces—except in minimal circumstances, but they do allow the construction of “conditioned” crawlspaces. The distinction is important and necessary.

Unvented, conditioned crawlspaces with insulation on the perimeter perform better in terms of safety and health (pest control), comfort (warm floors, uniform temperatures), durability (moisture), and energy consumption than passively vented crawlspaces with sub-floor insulation. This is because they are calmer and dryer in the summer, which minimizes condensation on framing surfaces. In addition, there is less heat loss from home during winter, which results in more comfortable floors and less risk of freezing pipes. Crawlspace temperatures, dew points, and relative humidities should mirror the house interior.

Crawlspaces should be designed and constructed as mini-basements, as part of the house within the conditioned space. To meet code requirements, the crawlspace floor should:

  • be covered with a ground cover consisting of 6-millimeter plastic that is overlapped and sealed at the edges and secured to the side walls;
  • perimeter walls should be insulated to code-specified levels (e.g., rigid foam on the exterior or inflexible fiberglass, spray foam, or rigid foam on the interior); and
  • Perimeter drainage should be provided just like a basement when the crawlspace ground level is below the ground level of the surrounding grade.

The crawlspace can be conditioned in one of three ways:

  1. supply air from the home to the crawlspace,
  2. return air to home via transfer grille or to outside via exhaust fan, or
  3. connect the crawlspace to a conditioned basement.

A soil gas venting system should be installed as part of a complete radon-resistant construction system.

Research encourages using slab-on-grade foundations rather than crawlspaces for locations not subject to frequent flooding.

A water heater tank should be installed inside a water heater drain pan in a dwelling where a leak from the tank could cause damage to the structure or property.  The pan is intended to catch water leaks from the tank or associated connections or condensate from the tank.  The pan should be made of galvanized steel or other approved material.  Pre-fabricated aluminum and plastic pans are standard and widely used.  Aluminum and plastic pans may not be allowed by every authority having jurisdiction (AHJ) or code official because they are not made of galvanized steel, and some tank manufacturers require a metal pan only.

Water Heater Drain Pan

Water Heater Drain Pan

A relief-valve pipe terminating into a water leak catch pan is not permitted because the pan is not an indirect waste receptor.  Most pans have only a ¾-inch-diameter drain outlet, which is incapable of using gravity to drain the pressurized discharge of the relief valve at full flow.

The pan should not be less than 1-1/2 inches deep.  The pan should be of sufficient size and shape to catch all dripping water or condensation leaks.  The pan should be drained by an indirect waste pipe having a minimum diameter of 3/4-inch.  The pan drain must not be reduced in size over its entire length because a reduction will act as a restriction and will impede the discharge.

The pan must not connect directly to the drainage system.  The water heater drain pan should terminate over a suitably located indirect waste receptor or floor drain or extend to the exterior.  An air gap must be provided to prevent backflow when the pan drain terminates into an indirect waste receptor or a floor drain.  When the pan ceases at the exterior of the dwelling, it should terminate at least 6 inches and, at most, 24 inches above the adjacent ground surface.  This makes the pan low enough not to be a nuisance and high enough to prevent the pan drain from becoming blocked by vegetation, snow, or ice.

A wood-burning stove (also known as a wood stove) is a heating appliance made from iron or steel capable of burning wood fuel. Unlike a standard fireplace, a wood stove is typically contained entirely within the living space rather than inset in a wall.







Wood stoves come in many different sizes, each suited for another purpose.

Small stoves are suitable in single rooms, seasonal cottages, or tiny, energy-efficient homes. These models can also be used for zone heating in large houses where supplemental heating is needed.

Medium-size stoves are appropriate for tiny heating houses or mid-size homes that are intended to be energy-efficient and as inexpensive as possible.

Large stoves are used in larger or older homes that leak air and are located in colder climate zones.

To ensure the safe and efficient use of wood-burning stoves, inspectors can pass along the following tips to their clients:


  • Burn coal. Coal burns significantly hotter than wood, posing a fire hazard.
  • Burn materials that will emit toxic chemicals, such as wood that has been pressure-treated or painted, colored paper, gift wrapping, plastic, plywood, particleboard, or questionable wood from the furniture.
  • Burn wet wood. Generally speaking, it takes six months for cut, stored timber to dry out and be ready for use in wood-burning stoves.
  • Burn combustible liquids like kerosene, gasoline, alcohol, or lighter fluid.
  • Let small children play near a lit wood-burning stove. Unlike standard fireplaces, whose sides are primarily inaccessible, all sides of wood stoves are exposed and capable of burning flesh or clothing.
  • Let the fire burn while the fire screen or door is open.


  • use a grate to hold the logs so that they remain secured in the stove and the air can circulate adequately around them to keep the fire burning hot;
  • keep the damper open while the furnace is lit;
  • dispose of ashes outdoors in a water-filled, metal container;
  • check smoke alarms to make sure they are working correctly; and
  • periodically remove the stovepipe between the stove and the chimney so that it can be inspected for creosote. Homeowners may want to hire a professional to perform this service.

Drain Waste Vent Basics – Every trap and trap fixture should be vented. The purpose of venting is to protect the trap seal of each trap. The vent system reduces pressure differences in the drainage system. Venting protects the trap seals from positive pressures and siphonage. At least one vent pipe should extend to the outdoor air for a dwelling.

Drain Vent

Any vent’s minimum size is half the drain pipe’s required size but not less than 1-1/4 inches (32 mm). All vent and branch vent pipes should be sloped and connected to drain back to the drainage pipe using gravity.

The most common way of venting is to install a separate or individual vent for each trap or trapped fixture, which is then connected to the dwelling’s main venting system. The other venting methods include standard venting, wet venting, waste-stack venting, circuit venting, combination drain-and-vent, and island-fixture venting.

A standard vent is one vent that serves more than one fixture, functioning as an individual vent for each institution. Wet venting is venting single or double bathroom groups or combinations thereof, where one vent pipe may serve all the fixtures connected to the wet vent. Waste-stack venting is venting individual fixtures through a drainage stack, and the oversized stack functions as the vent. Circuit venting is venting up to eight fixtures with a single vent pipe. A combination drain-and-vent system is restricted to floor drains, sinks, and lavatories and relies on the oversized drain pipe. Island-fixture venting has a vent installed below the flood-level rim of the fixture before rising to connect to another vent.

Here are some essential terms and definitions related to different types of vents:

  • The stack is a general term to refer to any main vertical drain, waste, and vent (DWV) line that extends through at least one story of a building.
  • The waste pipe or waste stack conveys only liquid sewage, not containing fecal material. Waste pipes do not give human fecal matter.
  • DWV is the abbreviation for drain (or soil), waste, and vent piping used commonly in houses. The pipe will often be labeled “DWV.”
  • The soil stack or soil pipe conveys sewage containing fecal material. In the plumbing trade, “soil pipe” is a common name for the cast-iron drainage pipe. The term, however, is not specific to a cast-iron pipe and refers to any DWV drainpipe that conveys the discharge of water closets, urinals, or any other fixture that receives human waste.
  • The stack vent is provided for the waste stack. The stack vent is the extension of a soil or waste stack above the highest horizontal drain that is connected to the stack. This is the main commonly-observed observed pipe penetrating the sloped roof surface, and it may also be visible in the unfinished attic space. Generally, a stack vent extends to the open air and can serve as the main vent to which branch vents connect.
  • The vent stack is the vertical vent pipe installed primarily for providing air circulation to and from any part of the drainage system, which is the piping in a home that carries away sewage or other liquid waste.
  • local vent stack is a vertical pipe into which other pipe connections are made from the fixture side of traps. The local vent stack removes vapor or foul air from the fixture.
  • The building drain is the lowest pipe of a drainage system that drains the soil, waste, and other drainage pipes from inside, and it extends at least 30 inches beyond the exterior building walls. This is extended into the building sewer.
  • The building sewer is the piping that extends from the end of the building drain and connects to the public sewer, private sewer, or individual sewage system.