Dado- A groove cut into a board or panel intended to receive the edge of a connecting board or panel.

Damper- A metal "door" placed within the fireplace chimney. Normally closed when the fireplace is not in use.

Dampproofing - The black, tar like waterproofing material applied to the exterior of a foundation wall.

Datum- A reference point of starting elevations used in mapping and surveying.

Dead Bolt - An exterior security lock installed on exterior entry doors that can be activated only with a key or thumb-turn. Unlike a latch, which has a beveled tongue, dead bolts have square ends.

Dead Light - The fixed, non-operable window section of a window unit.

Dead Load - The weight of all permanent structural and nonstructural components of a building.

Deck, Decked -To install the plywood or wafer board sheeting on the floor joists, rafters, or trusses.

Decking- Usually referring to outside projects, the lumber that forms the floor surface. Decking fastens directly over the floor joists.

Dedicated Circuit - An electrical circuit that serves only one appliance (ie, dishwasher) or a series of electric heaters or smoke detectors.

Default- Breach of a mortgage contract (not making the required payments).

Deflection- The downward displacement of a structural member or system under load.

Degree Day - A unit for measuring the extent that the outdoor daily average temperature (the mean of the maximum and minimum daily dry-bulb temperatures) falls below (in the case of heating, see Heating Degree Day), or falls above (in the case of cooling, see Cooling Degree Day) an assumed base temperature, normally taken as 65 degrees Fahrenheit, unless otherwise stated. One-degree day is counted for each degree below (for heating) or above (in the case of cooling) the base, for each calendar day on which the temperature goes below or above the base.

Degree Hour - The product of 1 hour, and usually the number of degrees Fahrenheit the hourly mean temperature is above a base point (usually 65 degrees Fahrenheit); used in roughly estimating or measuring the cooling load in cases where processes heat, heat from building occupants, and humidity are relatively unimportant compared to the dry-bulb temperature.

De-humidistat- A control mechanism used to operate a mechanical ventilation system based upon the relative humidity in the home.

Delamination- Separation of the plies in a panel due to failure of the adhesive. Usually caused by excessive moisture.

Demography- The study of the statistics of a human population in respect to trends in size, density, age, and economic characteristics, to identify markets.

Desanco Fitting - A type of compression adapter that connects tubular brass fittings to PVC pipe.

Dew Point Temperature - The temperature at which water vapor condenses in cooling air at the existing atmospheric pressure and vapor content. Cooling at or below the dew point will cause condensation.

Disconnect- A large (generally 20 Amp) electrical ON-OFF switch.

Discount Rate - A mortgage interest rate that is lower than the current rate for a certain period of time, e.g. 2.00% below variable rate for 2 years.

Dishwasher Tailpiece - A flanged adapter connecting a basket strainer to the drainpipe with a dishwasher inlet.

Diverter - Valves, which direct water to various outlets. They are used in showers, tubs, and sinks.

Door Bumper - An obstruction installed to prevent a door or lock from contacting another object.

Door Closer - A door closer is a mechanical device that closes a door.

Doorjamb, Interior - The surrounding case into which and out of which a door closes and opens. It consists of two upright pieces, called side jambs, and a horizontal head jamb. These 3 jambs have the "door stop" installed on them.

Door Operator - An automatic garage door opener.

Door Stop - The wooden style that the door slab will rest upon when it's in a closed position.

Door Sweep - Weather-stripping that mounts to the bottom of the door. It consists of an extruded aluminum strip that holds a flexible vinyl strip.

Door Swing - The direction and degree to which a door opens, as LH 90º, RH 180º, etc.

Door Viewer - A device with one or more lenses, mounted in a door at eye level, which allows a limited view through a door.

Dormer- A structural element of a building that protrudes from the plane of a sloping roof surface. Dormers are used, either in original construction or as later additions, to create usable space in the roof of a building by adding headroom and usually also by enabling addition of windows.

Dormer Window – Vertical window in a dormer for lighting a room adjoining a sloping roof.

Double Bullnose - A type of trim with the same convex radius on two opposite sides.

Double Cylinder - A lockset which is keyed both sides, requiring a key to lock or unlock from either side.

Double Glass - Window or door in which two panes of glass are used with a sealed air space between. Also known as Insulating Glass.

Double Headed Nail - A nail with two closely spaced heads to permit easy removal; widely used in concrete formwork as a temporary fastener; also called a Duplex Nail.

Double Hung Window - A window with two vertically sliding sashes, both of which can move up and down.

Double Plate - The two wood plates on the top of a wood framed wall

Dovetail Nailing - Nails driven through one piece of wood at opposing angles into another piece thus making it difficult for the timbers to be pulled apart.

Dowel- A short length of wood, round in section, used for a variety of purposes such as joining timbers, plugging fixing holes etc.

Down Payment - The difference between the sales price and the mortgage amount. A down payment is usually paid at closing.

Downspout- A pipe, usually of metal, for carrying rainwater down from the roof's horizontal gutters.

Drain Tile - A perforated, corrugated plastic pipe laid at the bottom of the foundation wall and used to drain excess water away from the foundation. It prevents ground water from seeping through the foundation wall. Sometimes called perimeter drain.

Draw- The amount of progress billings on a contract that is currently available to a contractor under a contract with a fixed payment schedule.

Drift Pin - A tapered steel shaft used to align bolt holes in steel connections during construction.

Drip- (a) A member of a cornice or other horizontal exterior finish course that has a projection beyond the other parts for throwing off water.(b) A groove in the underside of a sill or drip cap to cause water to drop off on the outer edge instead of drawing back and running down the face of the building.

Drip Cap - A molding or metal flashing placed on the exterior topside of a door or window frame to cause water to drip beyond the outside of the frame.

Drip Edge - A device designed to prevent water from running back or under an overhang.

Drip Groove - A groove cut in the underside of a projection (such as a window sash or sill) to cause rainwater to drip to the ground rather than running under the projection onto the main structure.

Drip Leg - A stub end pipe placed at a low point in the gas piping to collect condensate and permit its removal.

Drip Loop - A loop that is made in the drop wires just in front of the weather head. The drip loop prevents water from dripping down the wires and into the weather head.

Drive-In Latch - A latch without a mortised faceplate installed by driving the latch into an edge bore.

Dry in - To install the black roofing felt (tar paper) on the roof.

Dry Rot - A fungous disease that causes lumber to become brittle and crumble.

Drywall (or Gypsum Wallboard (GWB), Sheet rock or Plasterboard) - Wall board or gypsum- A manufactured panel made out of gypsum plaster and encased in a thin cardboard. Usually 1/2" thick and 4' x 8' or 4' x 12' in size. The panels are nailed or screwed onto the framing and the joints are taped and covered with a 'joint compound'. 'Green board' type drywall has a greater resistance to moisture than regular (white) plasterboard and is used in bathrooms and other "wet areas".

Drywall Returns - A type of construction in which the windows have drywall installed from the interior wall surface to the window unit. Another method of trimming windows is to have wood returns from the window to the wall surface. With wood returns you need window casing to frame the inside of the window. With drywall returns you have a cornerbead drywall corner and no window casing.

Ducts- The heating system. Usually round or rectangular metal pipes installed for distributing warm (or cold) air from the furnace to rooms in the home. Also a tunnel made of galvanized metal or rigid fiberglass, which carries air from the heater or ventilation opening to the rooms in a building.

Due-on-sale- A clause in a mortgage contract requiring the borrower to pay the entire outstanding balance upon sale or transfer of the property.

Dummy Trim - Hardware trim only, without a lock, usually used on the inactive door in a pair of doors.

Duplex - A building that is divided into two living units or residences, usually having separate entrances.

Duplex Receptacle - The commonly used receptacle (outlet). Called "duplex" because it has two plug-in sockets.

Dura Board, Dura Rock - A panel made out of concrete and fiberglass usually used as a ceramic tile backing material. Commonly used on bathtub decks. Sometimes called Wonder board

Dutch Door - Door that contains two half slabs mounted one above the other. Each slab is attached to the jamb with hinges and may swing independently of the other.

Dutch Door Bolt - A bolt which secures the top section of a Dutch door to the bottom section.

Dwarf Wall - A low wall, not as high as the storey of a building, often used as a garden wall or fence.

Dwelling Unit - A suite operated as a housekeeping unit, used or intended to be used as a domicile by 1 or more persons and usually containing cooking, eating, living, sleeping and sanitary facilities.

DWV (Drain-Waste-Vent) - The section of a plumbing system that carries water and sewer gases out of a home.

Dynamic Load - Any load that is non-static, such as a wind load or a moving live load.