First, some terms we'll be using:

The stair body consists of: stringers, the sides of the stair which are routed to accept the treads (part you step on) and risers (vertical front part of the step).

The balustrade consists of: the newels, balusters and handrail. The newels are the larger vertical posts seen at the beginning and end and as additional supports in long stretches
of rail to give strength to the balustrade. The balusters are the smaller, more numerous vertical posts that support the handrail between the newels. Sometimes a half wall replaces the
balustrade completely.

The balustrade is arranged either "Post to Post"
or "Over the Post"

1. What Kind of Stair?

Straight	Flare	Curve	Spiral
Can be split with a landing for a U or L stair	The first several steps flare out to give the look of a curved stair	The shape follows a constant radius or arc of a circle.	Used where space is limited; stair is supported by a center pole. See Spirals for options.

2. How open do you want the stair to be?
On any straight, flare or curved stair, part (or all) of the side wall showing above the stair can be open to the entry or next room-on one or both sides.

Partial Open Stair	Double Partial Open	Full Open	Double Full Open

3. How does the stair look from the side?
The open portion can have returned treads or a closed stringer with knee wall.

Returned Tread The side edge of the tread is seen from the open side of the stair. A mitered "return" is added to the tread to give a finished side edge.	Closed Stringer Treads are not seen from either side & are fitted into a groove (or "rout") in the stringer. A short framed wall (knee wall) holds the balusters.	Box Newel & Knee wall Easier to install and finish, a knee wall can also be dressed up with a box newel and unusual balusters.
A stair with returned treads is a more traditional, finished look. A closed stringer with knee wall is an updated, less costly way, to achieve openness.

Returned treads will be more. Material is usually stain-grade hardwoods & the miter adds production cost.

A closed stringer stair can have stain-grade hardwood treads but usually has carpet-grade or hybrid treads which are less.

Curbing is more costly than returned treads on a curve due to the thicker laminations required.

An outside flare and cylinder will also add to the cost.

4. How open do you want the underneath of the stair?
A stair can be fully supported underneath by two walls, supported only by the outside wall (called "inside radius free-standing" on a curved stair) or without the support of any walls (free-standing).

Fully Supported	Inside Radius Free Standing	Free Standing

5. What about the first few steps?

The first step may be the same width as the rest of the stair	Or width can be added at the bottom with a Bullnose Starting Step	Or several treads bowed (usually first 3-4 treads)

Besides it's initial higher cost, a bullnose requires a volute and additional balusters. A double bullnose doubles that cost.

A standard box newel can be added to a regular starting step for a little less than a bullnose and volute.

Bowed treads cost more than straight treads.