Stairs on a floor plan
A stair on a floor plan is a set of parallel lines for the treads, an arrow marked UP that starts on the bottom step, and a zigzag break line where the plan cuts through the flight. Below are those marks drawn, the same stair on both floors, the common stair shapes, and how to count the risers and check them against the building code.
How a stair is drawn on each floor
A floor plan is the house seen from above, cut part of the way up the walls. A stair rises through that cut, so the ground floor plan shows only the lower part of the flight. The rest is above the cut, and the drawing either dashes it or leaves it out. Upstairs, you look down on the whole flight through the opening in the floor, so every tread is drawn.
- The arrow starts on the bottom step and is marked UP. It points the way you climb.
- The break line is where the plan cuts through the flight. Everything past it is above the cut.
- Treads above the cut are dashed, or left out. Whatever is under the stair, such as a CR or a storeroom, is drawn in full.
- Upstairs the arrow starts at the top step and is marked DN. Some offices keep one UP arrow from the bottom on every plan, so read the arrow from its start.
- A guard rail runs along the open side of the stair well, drawn as a thin double line.
Stair shapes and their symbols
The shape of the stair decides how much floor it takes and where it lands. On a plan the shape is easy to read: follow the arrow from UP to its head.
- Straight stair One flight in a line. The simplest to build, and it needs the longest clear run of floor.
- L-shaped stair Two flights at a right angle with a square landing at the turn. It fits into a corner.
- U-shaped or dog-leg stair Two flights side by side, turning back on a half landing. It packs a full storey into a short, wide space.
- Winder stair An L or U stair whose turn is made of wedge-shaped treads in place of a landing. It saves space but needs care: the code sets a minimum tread on the narrow side.
- Spiral stair Wedge treads round a centre post, drawn as a circle with radiating lines. It takes the least floor, and it is hard to carry furniture up.
- Straight stair with a landing One line of travel broken by a landing. Section 1207(e)(7) of PD 1096 caps the height between landings at 3.60 m.
Counting the risers on a plan
Count the lines across the flight. Each one is the edge of a step, and the space between two lines is a tread. A straight flight has one tread fewer than it has risers, because the last riser steps up onto the floor above, and the floor itself is the top tread. Many plans write the count beside the arrow, such as 17R, with the riser height on the section.
A worked example. The floors are 3.00 m apart. The code allows a riser of up to 200 mm, which would take 15 risers, but a gentler stair is easier every day, so say 17 risers of about 176 mm. That is 16 treads, and at a run of 250 mm each the flight is 4.00 m long in plan, before the space to step on and off at either end. The stair dimensions checker does this arithmetic for any floor height and checks the result against the code.
What the building code asks of a house stair
These are the figures from the National Building Code, PD 1096, that you can check from a floor plan and its section. The plan gives the width, the run and the number of treads. The section gives the rise and the headroom.
| Rule | Figure | Where it comes from |
|---|---|---|
| Rise of each step | 200 mm at most | PD 1096 Section 1207(e)(2): "shall not exceed 200 millimeters". Section 708(h) gives a dwelling "a rise of 200 millimeters" |
| Run of each step, as Section 708(h) says for dwellings | 200 mm at least | PD 1096 Section 708(h), Minimum Requirements for Group A Dwellings |
| Run of each step, as Section 1207(e)(2) says for every stairway | 250 mm at least | PD 1096 Section 1207(e)(2), for every stairway serving any building; a private stairway serving fewer than 10 people also keeps 250 mm |
| Clear width of a house stair | 750 mm at least | PD 1096 Section 708(h), and Section 1207(e)(1) for a private stairway serving fewer than 10 people |
| Headroom above the nosings | 2.00 m at least | PD 1096 Section 1207(e)(12), measured vertically from a line through the tread nosings to the soffit above |
| Height between landings | 3.60 m at most | PD 1096 Section 1207(e)(7) |
| Landing depth | the stair width | PD 1096 Section 1207(e)(5): need not exceed 1.20 m on a straight run |
Two sections of the decree give two different runs, 200 mm and 250 mm. The National Building Code guide explains why, and which one a designer should plan to.
Checking the stair on your own plan
- Follow the arrow. It should start in a hall or living area, and land upstairs somewhere every bedroom can be reached from without passing through another room.
- Look for doors. No door should swing across the bottom or the top step. Check the arcs of the doors nearby on the floor plan symbols legend.
- Look for dashed lines over the stair. A dashed beam crossing the flight may cut the headroom. The section shows whether 2.00 m is kept above every nosing.
- Count the treads. Multiply by the run and compare with the length drawn. If the numbers do not agree, ask which one is right before anything is built.
- Check the space at each end. A landing at least as deep as the stair is wide gives room to turn with a load.
Where the stair goes shapes a two-storey house more than any other choice, as the two-storey house design guide explains, and a loft often needs a steeper, more compact stair. The guide to reading a house plan sets out every sheet the stair appears on.
The other symbols drawn in detail: sliding doors and windows.