General Proportions:

Rectangular blocks; temple-form massing.

Roof types and Features:

A simple gable, with low pitch, reflecting rake of the pedimented end.  Roof may not be visible in larger example or behind cornice and parapet.  In peripteral examples (columns extending along three sides or around the house), the roof is hipped.  No dormers.

Fenestration:

Window are universally trabeated, that is, with flat lintels.  Six-over-six windows, with ground-floor windows often taller than second-story windows.  Three-story examples often have half or considerably smaller attic windows.  Window surrounds can be quite heavy, with entablatures and details that imitate the main entablature of the house.

Structural and Facework Materials:

Brick, wood, and masonry walls, with wood being the most common.  Details, such as columns, entablatures, and window frames almost always wood.

Spatial Designation and Floor Plan:

Usually one and a half to two main stories (attic story in urban versions).  Rectangular temple form plans, often with ell-shaped wings to one side or both sides of main block.  Gable end faces the street.  Larger examples have entrance in center, while the entrance is often to the side in smaller, three-bay versions.  Temple form may be a simple pediment or pediment with a complete classical entablature above a columned portico.  A fan in the gabe end is often found in vernacular examples.  Corner pilasters.

Chimney Placement:

Slender chimneys at the eaves; chimneys often not visible from the front.

Entranceway Attributes:

Even the plainest of examples will have flanking pilasters, but doorways can be quite elaborate, with engaged columns, sidelights, transoms, and entablatures composed of Greek frets, palmettes, and acroteria at the corners.  A recessed doorway, with columns, especailly Doric and set in antis, was also popular.

Color:

Historically, most were white when built, with dark green shutters.

excerpt from The Abrams Guide to American House Styles by William Morgan