Dado rail:

A decorative, horizontal timber moulding located on an internal wall at approximately waist height.

Damp proof course:

An impermeable layer of material built into a wall, usually just above ground level, preventing moisture rising up the wall,
or
a chemical solution injected into the base of a wall as a means of preventing moisture rising up the wall.

Damp proof membrane:

A continuous, impermeable membrane preventing moisture rising up through a solid floor.

Domelight:

A raised window set within a flat roof.

Dormer:

A window or other structure projecting out from a sloping roof to provide additional space in an attic room.

Downpipe / downcomer:

A vertical drainage pipe conducting rainwater to the ground.

Dressed stonework (or ashlar):

Squared and smooth faced stonework laid in regular courses.

Dry rot:

The term given to a destructive fungal decay in timber which can spread rapidly.