This chapter covers all the knowledge required for the Red Seal exam concerning the design, calculation, fabrication, and installation of stairs, ramps, and architectural millwork. You must master not only the calculation formulas but also the requirements of the National Building Code (NBC) and the installation principles that ensure safety and durability. This module represents a significant portion of the theoretical exam; a calculation error or a lack of knowledge about minimum clearances can cost you valuable points.
Reference Standards and Codes
In Canada, the design and installation of stairs and ramps are governed primarily by the National Building Code of Canada (NBC) , published by the National Research Council (NRC). Provincial and territorial editions refer to it almost entirely. For the Red Seal exam, you must know the requirements of the NBC, current edition, without reference to provincial amendments.
The relevant sections of the NBC are:
Section 3.4 : Safety requirements for exits (exit stairs)
Section 9.8 : Stairs, ramps, guards, and handrails (small buildings)
Section 9.9 : Guards and windows
The Canadian Electrical Code, Part I (CE Code) may apply when installing lighting under stairs or receptacles near ramps, but this is beyond the scope of this chapter. Standard CSA B44 (elevators) applies only to escalators, which are outside our field.
Essential Definitions
Before anything else, master the exact terminology used in plans and specifications:
Term
Definition
**Riser**
Vertical element between two consecutive treads. Its height is measured from top of tread to top of tread.
**Run (Tread depth)**
Horizontal depth of a step, measured from the nosing of the tread to the vertical projection of the nosing of the next tread.
**Nosing**
Projecting front edge of a tread, usually rounded or beveled.
**Headroom**
Vertical clear height above the steps, measured vertically from the nosing of the tread to the ceiling or any obstruction.
**Line of travel (Walking line)**
Imaginary line located 300 mm from the narrowest side of a stair, along which the run is measured.
**Kite winder (Narrow end)**
Minimum width of a tread in a spiral or winding stair, measured at 150 mm from the inner stringer.
**Stringers**
Inclined members supporting the treads. We distinguish the center stringer, side stringers, and the cut stringer (open stringer).
**Stair width**
Usable width of a stair, measured between the inside faces of the stringers or guards.
**Landing**
Flat horizontal surface located between two flights of stairs.
**Handrail**
Continuous element grasped by hand to ensure balance.
**Guard**
Protective barrier installed on the open sides of a stair, landing, or mezzanine.
Fundamental Stair Calculations
The Blondel Formula
The relationship between riser height (h) and run (g) is governed by the Blondel formula, which expresses the comfort and safety of a stair:
2h + g = 630 mm (target value between 600 and 640 mm)
This formula is the basis of all stair calculations. For a comfortable stair, aim for 630 mm. The acceptable extreme values are 600 mm (steep stair) and 640 mm (very comfortable stair).
Step-by-Step Calculation Method
Let's take a concrete example: height to be covered of 2800 mm (from finished floor of the lower level to finished floor of the upper level).
Step 1 — Determine the number of risers:
Divide the total height by a target riser height (180 mm):
2800 ÷ 180 = 15.56 → round up to 16 risers.
Step 2 — Calculate the exact riser height:
2800 ÷ 16 = 175 mm. This value is compliant (max. 180 mm according to the NBC for residential buildings).
Step 3 — Determine the number of runs:
The number of runs is always equal to the number of risers minus one (the last step opens onto the upper landing). Here: 16 − 1 = 15 runs.
Step 4 — Calculate the run:
Apply the Blondel formula: 2(175) + g = 630 → g = 630 − 350 = 280 mm. This run is compliant (minimum 255 mm according to the NBC).
Step 5 — Calculate the total length of the stair:
15 runs × 280 mm = 4200 mm (not including the upper landing).
Winding and Spiral Stairs
For winding stairs (tapered treads), the run is measured on the line of travel (at 300 mm from the inner stringer). The kite winder (measured at 150 mm from the inner stringer) must never be less than 150 mm. The winding must begin at a minimum distance of 300 mm from the start of the flight.
National Building Code (NBC) Requirements
Mandatory Step Dimensions
The following table summarizes the NBC requirements (Section 9.8) for small residential buildings:
Parameter
Minimum Requirement
Maximum Requirement
Riser height
125 mm
180 mm
Run (measured at the line of travel)
255 mm
355 mm
Headroom
2050 mm
—
Stair width
860 mm (residential)
—
Variation between adjacent risers
0 mm (3 mm tolerance)
—
Variation between adjacent runs
0 mm (3 mm tolerance)
—
Important : The 3 mm tolerance between adjacent risers is a strict requirement. A variation of more than 3 mm between two consecutive steps is a frequent cause of tripping and constitutes a major non-compliance during an inspection.
Exit Stairs (Section 3.4)
For high-rise buildings or exits, the requirements are more severe:
Minimum stair width: 1100 mm
Riser height: max. 180 mm
Run: min. 280 mm
Headroom: min. 2050 mm
Stairs must be of non-combustible material or protected
Access Ramps (Section 3.8)
For universal accessibility, ramps must comply with:
Maximum slope: 1:12 (8.33%)
Minimum width: 900 mm
Rest landing: every 9 m of length, with a minimum length of 1500 mm
Handrail on both sides, at a height of 865 mm to 965 mm
Slip-resistant surface
Guards and Handrails
Regulatory Heights
Location
Minimum Guard Height
Stair (open side)
900 mm above the nosing of the treads
Landing or mezzanine
1070 mm above the finished floor
Exit stair (high-rise building)
1070 mm
Access ramp
900 mm (with handrail at 865-965 mm)
Handrail Requirements
The handrail must be continuous over the entire flight, including at intermediate landings.
The clear space between the handrail and the wall must be at least 50 mm.
The diameter of the handrail must be between 30 mm and 43 mm (circular cross-section) or equivalent for non-circular sections.
The handrail must be installed at a height of 865 mm to 965 mm, measured vertically from the nosing of the tread.
It must be able to support a concentrated load of 0.9 kN applied at any point.
Baluster Spacing
The maximum spacing between balusters (or between the baluster and the stringer) is 100 mm. This measurement is intended to prevent the passage of a 100 mm diameter sphere, thus preventing a child's head from getting trapped. This requirement applies to all guards, regardless of the type of building.
Guard Design Loads
Guards must resist:
A concentrated load of 0.9 kN applied at any point (upward, downward, or horizontally)
A linear load of 0.5 kN/m applied horizontally at the top
Architectural Millwork: Doors, Windows, and Trim
Interior Door Installation
The installation of an interior door follows a precise sequence:
73.Checking for square: The frame must be square (tolerance of 1 mm per 300 mm of height). Use a level and a carpenter's square.
74.Frame fastening: The frame is fastened to the rough opening using shims and screws or nails. Shims must be placed at fastening points (hinges and strike plate) to prevent twisting.
75.Installation clearance: The clearance between the door and the frame must be 2 to 3 mm on the sides and top, and 8 to 10 mm at the bottom (to allow for air passage and clearance for carpets).
76.Hinges: Two hinges for doors up to 2.1 m in height; three hinges beyond that. Hinges are installed at 150 mm from the top and 200 mm from the bottom.
77.Final check: The door must open freely without rubbing, and remain in position when opened at 45°.
Window Installation
Window installation must ensure air and water tightness:
80.Sill: The window rests on plastic or treated wood shims, placed at the quarter points of the width.
81.Fastening: Fastening tabs are spaced at 400 mm maximum, at 150 mm from the corners.
82.Sealing: A weather-resistant barrier tape is applied around the perimeter, with a 100 mm overlap at the joints. The tape is applied starting at the bottom, then the sides, then the top ("bottom-first" principle).
83.Insulation: Expanding foam or mineral wool is inserted between the frame and the rough opening, without compressing the frame.
84.Installation clearance: A clearance of 10 to 15 mm is left between the frame and the rough opening to allow for thermal expansion.
Trim and Moldings
Interior trim (chair rails, baseboards, door casings) must be installed with precision:
Baseboards: Installed with 45° miter joints at interior and exterior corners. Interior corners can also be done with a coped joint to prevent the joint from opening due to wood shrinkage.
Chair rails: Installed at a uniform height, generally between 800 and 1200 mm from the finished floor.
Door casings: Composed of two jambs and a header, assembled with miter or mortise-and-tenon joints. Miters must be glued and nailed without any visible gap.
Prefabricated Stairs vs. Custom Stairs
Prefabricated Stairs
Prefabricated stairs (factory-machined) offer several advantages:
Reduced cost (mass production)
Quick installation (often in a single piece)
Consistent quality (CNC machining)
Guaranteed compliance with standards
Disadvantages : Less flexible for irregular configurations; delivery lead times; difficulty adapting on site.
Custom Stairs
Custom stairs (built on site or in a workshop) offer:
Perfect adaptation to the actual dimensions of the building
Disadvantages : Higher cost; longer fabrication time; dependence on the carpenter's skill.
Stair Installation Procedures
Site Preparation
106.Dimension check: Measure the total height (from finished floor to finished floor) at several locations to detect variations.
107.Squareness check: Adjacent walls must be square; otherwise, adjust the stringers accordingly.
108.Stringer preparation: Stringers are cut according to the calculated template, leaving 25 mm of material below the last tread for strength.
Stringer Installation
110.Upper stringer fastening: The stringer is fastened to the upper landing structure using metal brackets or wood screws of 100 mm minimum.
111.Lower stringer fastening: The stringer rests on the lower floor, fastened using metal angles.
112.Alignment check: Stringers must be parallel and level. Use a laser level or a plumb bob.
Tread and Riser Installation
114.Risers first: Risers are installed first, nailed to the stringers with 50 mm finish nails.
115.Treads next: Treads are installed on top of the risers, fastened with wood glue and 65 mm finish nails.
116.Nosing: The nosing is installed last, fastened with nails or hidden screws.
Railing and Guard Installation
118.Posts: Railing posts are fastened to the structure (stringer or floor) using bolts or metal brackets. They must be perfectly plumb.
119.Handrail: The handrail is fastened to the posts at the regulatory height (865-965 mm).
120.Balusters: Balusters are installed between the handrail and the stringer, spaced at 100 mm maximum.
Advanced Calculations and Useful Formulas
Calculating the Number of Steps for a Stair with a Landing
When an intermediate landing is required (total height > 3.7 m), divide the total height into two equal flights. Each flight must have the same number of risers (within ±1) to maintain consistency.
Calculating the Pitch of a Stair
The pitch of a stair is calculated as follows:
Pitch (%) = (riser height ÷ run) × 100
For a comfortable stair, the pitch is between 30° and 35°. Beyond 40°, the stair is steep and uncomfortable.
Calculating the Length of a Stringer
The length of the stringer (hypotenuse) is calculated using the Pythagorean theorem:
L = √(H² + P²)
Where H = total height of the stair and P = total horizontal projection (sum of the runs).
Table of Compliant Riser/Run Combinations
Riser (mm)
Minimum Run (mm)
Comfortable Run (mm)
Pitch (°)
160
255
310
27.3
165
255
300
28.8
170
255
290
30.4
175
255
280
32.0
180
255
270
33.7
Frequent Errors and Quality Control
Common Defects to Avoid
136.Uneven steps: The height variation between adjacent risers exceeds 3 mm. This defect is dangerous because the human brain adapts to the rhythm of the steps and trips on an irregularity.
137.Uneven runs: Same problem as above, but for the depth of the steps.
138.Insufficient headroom: A beam or low ceiling reduces headroom below 2050 mm. Always check headroom before finalizing calculations.
139.Non-compliant nosings: The nosing must not project more than 25 mm beyond the run. Nosings must be identical throughout the stair.
140.Interrupted handrail: The handrail must be continuous, including at landings. An interruption is a non-compliance.
Quality Control Before Inspection
Check the squareness of the stringers with a 300 mm square.
Check the level of the landings with a level of 1200 mm minimum.
Check the plumbness of the posts with a plumb bob.
Check the spacing of the balusters with a 100 mm gauge.
Check the height of the guards with a tape measure.
Pitfalls to Avoid (Red Seal Exam)
148.Confusing run and tread depth: The run is measured from the nosing of one tread to the nosing of the next tread, not from the front face of the riser to the back face of the tread. This distinction is crucial in calculations.
149.Forgetting that the number of runs = number of risers − 1: This is the most frequent error in stair calculations. The last step opens onto the landing; it has no run.
150.Using the rough height instead of the finished height: Calculations must be based on finished floor-to-finished floor heights, not structural heights. An error of 20 mm of flooring material can make the entire stair non-compliant.
151.Neglecting the 3 mm tolerance: The exam will often ask you to calculate whether a variation is acceptable. Remember: 3 mm maximum between adjacent risers, and 6 mm maximum over the entire stair.
152.Confusing guard heights: 900 mm for stairs, 1070 mm for landings and mezzanines. This distinction is often tested.
153.Forgetting the 100 mm baluster spacing: This requirement applies even if the guard has a compliant height. A spacing of 110 mm is a non-compliance.
154.Calculating the slope of an access ramp in degrees instead of ratio: The slope of an access ramp is expressed as a ratio (1:12), not in degrees. A slope of 1:12 corresponds to approximately 4.8°.
155.Ignoring the line of travel: For winding stairs, the run is measured at 300 mm from the inner stringer, not at the center of the stair. This measurement error can make a stair non-compliant.
156.Not checking headroom under beams: The 2050 mm headroom must be checked at every step, not just at the beginning of the stair. A diagonal beam can reduce headroom mid-flight.
157.Confusing handrail and guard: The handrail is a gripping element; the guard is a protective barrier. A stair can have a handrail without a guard (stair between two walls), but a guard without a handrail is not compliant.
Summary
The Blondel formula (2h + g = 630 mm) is the basis of all comfortable and safe stair calculations.
NBC requirements (Section 9.8) mandate: riser 125-180 mm, run 255-355 mm, headroom 2050 mm, stair width 860 mm minimum.
The number of runs is always equal to the number of risers minus one.
Tolerances are strict: 3 mm maximum between adjacent risers, 6 mm over the entire stair.
Guards must be 900 mm high on stairs and 1070 mm on landings; baluster spacing must not exceed 100 mm.
Handrails must be continuous, at 865-965 mm from the nosing of the treads, with a 50 mm clearance from the wall.
Access ramps must have a maximum slope of 1:12, with rest landings every 9 m.
Door installation requires clearances of 2-3 mm on the sides and 8-10 mm at the bottom; hinges are installed at 150 mm from the top and 200 mm from the bottom.
Window installation follows the "bottom-first" sealing principle with a 100 mm overlap at the joints.
Stringer calculations use the Pythagorean theorem: L = √(H² + P²).
Self-Assessment Questions
170.A stair must cover a height of 2900 mm. Calculate the number of risers, the exact height of each riser, the number of runs, and the run compliant with the Blondel formula.
171.What is the minimum height of a guard on an exit stair landing in a high-rise building?
172.A winding stair has a kite winder of 140 mm. Is this compliant? Justify your answer.
173.What is the maximum slope of an access ramp for persons with disabilities, and what is the maximum length between two rest landings?
174.How many hinges does an interior door of 2.1 m in height require, and at what distances from the top and bottom must they be installed?
175.What is the maximum spacing between balusters of a guard, and why is this value imposed?
176.A stair has 14 risers of 175 mm and runs of 270 mm. Calculate the total length of the horizontal projection and the pitch in degrees.
177.What is the maximum tolerance for variation between two adjacent risers, and what is the maximum tolerance over the entire stair?
178.At what height relative to the nosing of the treads must a handrail be installed, and what is the recommended diameter?
179.When installing a window, in what order should the weather-resistant barrier tapes be applied around the perimeter?
