Major storm event

A rain or snow storm, or combined rainfall and snow melt event which produces stormwater runoff equivalent to that produced by the ten year to 100 year rainfall events.

Manufactured housing

These houses typically consist of a single module, almost entirely finished in the factory, placed on either a permanent or temporary foundation. These homes are usually built to the standards of a national code maintained by the US Department of Housing and Urban Development (HUD), which may be less stringent than state, regional or local codes for site-built housing. 

Marine climate

Marine climates have a mean temperature of the coldest month between 27°F and 65°F; a warmer month mean of less than 72°F; at least four months with mean temperatures over 50°F; a dry season in summer; the month with the heaviest precipitation in the cold season has at least three times as much precipitation in the rest of the year. The cold season is October through March in the Northern Hemisphere. The Greater Portland area is a marine climate.

Mass transit

Conveyance of persons or goods from one place to another on a local public transportation system such as light rail, bus, or subway.

MCS

See Multiple Chemical Sensitivity.

MDF

Medium-density fiberboard: a composite wood fiberboard, used for cabinetry and other interior applications. MDF containing urea formaldehyde can contribute to poor indoor air quality.

Measure life

The length of time that the demand-side management technology will last before requiring replacement. Also known as the technology life.

Mercury (Hg)

A metal that is an odorless silver liquid at room temperature, converting to an odorless, colorless gas when heated. Mercury readily combines with other elements, and accumulates in the environment. Mercury is toxic, and causes a range of neurological, organ, and developmental problems. Fluorescent lights and old thermostats are two building related products that can contain significant amounts of mercury. Newer fluorescent lights are available with substantially reduced amounts of mercury.

MERV

Minimum Efficiency Reporting Value: the rating standard for efficiencies of air filters. The higher the rating, the better the protection for the equipment and the occupants. Recommended ratings are MERV 8-14.

Methane (CH4)

An odorless, colorless gas, nearly insoluble in water, which burns with a pale, faintly luminous flame to produce water and carbon dioxide (or carbon monoxide if oxygen is deficient).

Microclimate

The small scale climate of a building site, affected by site geography, site topography, vegetation, and proximity to bodies of water, etc., which may very slightly from the prevalent regional climatic conditions.

Microturbine

A new technology fueled by natural gas, diesel or propane that generates both electricity and hot water. They have a compact size, small number of moving parts, are light weight, have lower emissions, more efficient and lower electricity costs.

Mildew

The discoloration caused by mold (see Mold).

Mini split (ductless) heat pump

These highly-efficient make good add-ons to houses with "non-ducted" heating systems. They can also be a good choice for room additions, small studios and accessory dwelling units (zonal control), where extending or installing distribution ductwork is not feasible. They are wall-mounted up high and have an outdoor compressor/condenser, and an indoor air-handling unit.

Mixed-humid climate

A region that receives more than 20 inches of annual precipitation, has approximately 5,400 heating degree days or fewer, and where the monthly average outdoor temperature that drops below 45°F during the winter months. This region has significant heating, significant cooling, high moisture levels most of the year, and many areas of moderate to high rainfall. Controlling the infiltration of moisture-laden air into the building enclosure and keeping moisture away from cold surfaces are major goals of design and construction. Ideally, wall and roof assemblies are designed to promote drying to both the interior and exterior in this climate.

Mixed-use development

A development in one or several buildings that combines several revenue-producing uses that are integrated into a comprehensive plan—such as a project with elements of housing, retail, and office space.

Modular housing

These homes are built from two or more factory-constructed modules with most finish materials in place.  They are transported to the building site on a truck and set on a permanent foundation with a crane. Modules are connected and finished on site. Modular housing is built to state and local codes. Also known as pre-fab housing.

Mold

A type of fungus that requires moisture and a food source to grow. Fungi do not contain any chlorophyll (and cannot make their own food); molds live off the food produced by plants or animals, or decaying matter. Molds are often parasites on plants, animals, or even other fungi. Molds reproduce with spores.  Mold is a common trigger for allergies.

Montreal Protocol

Treaty, signed in 1987, governs stratospheric ozone protection and research, and the production and use of ozone-depleting substances. It provides for the end of production of ozone-depleting substances such as CFCs. Under the Protocol, various research groups continue to assess the ozone layer. The Multilateral Fund provides resources to developing nations to promote the transition to ozone-safe technologies.

MRF

Material Recovery Facility: a facility where solid waste is sorted, separated and stored for recycling, or disposal, in landfill.

MSDS

Material Safety Data Sheet: form that contains brief information regarding chemical and physical hazards, health effects, proper handling, storage, and personal protection appropriate for use of a particular chemical in an occupational environment.

Mulch

A layer of material (wood chips, straw, leaves, etc.) placed around plants to hold moisture, prevent weed growth, and enrich or sterilize the soil.

Multiple Chemical Sensitivity

A diagnostic label for people who suffer multi-system illnesses as a result of contact with, or proximity to, a variety of airborne agents and other substances.