Dado – A rectangular groove in a board or plank. In interior decoration, a special type of wall treatment.

Damp Proof Course – A damp-proof material placed just above the ground level in a brick or stone wall to prevent ground moisture from seeping up through the structure.

Damp Proofing – The process of coating the outside of a foundation wall with a special preparation to resist passage of moisture through the wall. Material used to resist the passage of moisture through concrete floor slabs and from masonry to wood.

Datum – A reference point from that elevations and measurements are taken.

Datum Line – In surveying, the base line from that all lines or levels are taken.

Deck – The flat portion of a roof.

Deck Roof – Defined under “Roof Types”.

Deciduous – Pertaining to trees that shed their leaves annually. This condition is common to hardwood trees.

Defect – A fault or irregularity in lumber that detracts from utility, durability, strength, or appearance.

Deflection – A deviation or turning aside from a set line; bending of a beam or any part of a structure under an applied load.

Deformation – Alterations in forms that a structure undergoes when subjected to the action of weight or load.

Deformed Bar – Reinforcing bars made in irregular shapes to produce a better bond between the bars and the concrete. 

Dehumidify – To reduce by any process the quantity of water vapor or moisture content in the air of a room.

Diagonal Ties – Braces or ties that help stiffen a roof truss; braces attached to an angle to tie framing members together.

Dimension Stock – Dressed lumber cut to standard sizes that are readily available at local lumber dealers.

Direct Current – Defined under “Electrical Terms”.  0

Distributed Load – In building, a load spread over an entire surface or along the length of a beam.

Door Casing – The finishing material around a door opening.

Door Jamb – Sides of a frame set in a wall or partition on that the door is hung.

Door Sill – A horizontal member forming the bottom of an outside door frame over that the door closes.

Door Stop – A device fitted to the door or on the floor or wall near the door, to hold it open as far as may be required, or to prevent the door from being opened beyond a certain amount; the strip against that a door closes on the face of a door frame.

Dormer – Framing that projects from a sloping roof, providing an internal recess in the roof space.

Dormer Window – Defined under “Window Types”.

Double Glazing – Two panes of glass in a door or window, with an air space between the panes. They may be sealed hermetically as a single unit or each pane may be installed separately in the door or window sash.

Double Header – A structural member made by nailing or bolting two joists together for use where extra strength is required in the header, as at stair openings.

Double Hung Window – A window with an upper and lower sash, each balanced by springs or weights to be capable of vertical movement with relatively little effort.

Dovetailing – In carpentry, interlocking joints; joints made by cutting two boards or timbers to fit into each other.

Dowel – A pin of wood or metal used to hold or strengthen two pieces of timber where they join; a pin or tenon fitting into a corresponding hole serving to fasten two pieces of wood together.

Down-Draft – A draft created in a chimney when air currents enter at the top and travel down; sometimes caused by not carrying the chimney high enough above the ridge of the roof.

Downspout – A pipe that carries water from the eaves trough to the ground or the drainage system.

Draft Stop or Fire Stop – An obstruction placed in a concealed space to block the passing of flame of air currents upwards or across a building.

Drainage System – Defined under “Plumbing Terms”.

Drainage Tile – Clay or concrete pipe used in drainage around footings.

Dress – To plane one or more sides of a piece of sawn lumber.

Dressing – The operation of squaring or smoothing stones or lumber for building purposes.

Drier – Defined under “Paint”.

Drip – A construction member, wood or metal, that projects to throw off rainwater. A groove on the underside of a projecting part, such as a sill, serving the same purpose.

Drip Mould – A projecting moulding arranged to throw off rainwater from the face of a wall.

Drop Siding – Weatherboarding that is rabbeted and overlapped.

Dry-Kiln – A chamber for drying and seasoning lumber, artificially heated to a carefully controlled temperature.

Dry Rot – A decay of lumber due to the attack of certain fungi.

Drywall Construction – Defined under “Construction Types”.

Drywall Finish – Interior wall and ceiling finish other then plaster – e.g. gypsum board, fiberboard panels, plywood, etc.

Dry well – Defined under “Plumbing Terms”.

Ducts – In building construction, usually metal pipes, round or rectangular in shape, for distributing air in heating and ventilating systems.

Dwarf Wall – A wall of less than normal full height.

Dwelling, Multiple – Any building or part thereof designed intended or used for residential occupancy consisting of terraces, rows and group houses.