Stair Construction (Leaving Cert Construction Studies): Revision Notes

Stair construction

Basic components and materials

Timber stairs are typically constructed using pine, ash, or oak timber. The staircase is built within a designated space called a stairwell, usually positioned against an external wall for structural support.

Every staircase consists of three fundamental components:

• Two strings: The angled structural members that support the steps
• Steps: Made up of the horizontal tread and vertical riser sections

The strings serve as the main structural framework, whilst the treads provide the walking surface and risers close the vertical gaps between steps.

String types and construction methods

There are two main approaches to stair string construction, each offering different structural and aesthetic benefits.

Closed string construction

In closed string stairs, both the tread and riser components are housed within grooves cut into the string itself. This creates a continuous, uninterrupted appearance along the string's edge.

The construction process involves:

• Creating housing joints in the string to accommodate each step
• Using wedges and triangular glue blocks underneath each tread and riser
• Securing components with screws at 240mm centres
• Maintaining a 50mm margin from the string edge

Open string construction

Open string stairs feature a string that is cut to follow the profile of the steps. This exposes the ends of the treads and creates a more decorative appearance.

Key characteristics include:

• The string board is cut to accommodate step profiles directly
• Glue blocks are still used underneath for structural stability
• A return nosing may be attached to the exposed tread ends
• The construction allows for more elaborate finishing details

Structural connections and fixing methods

Newel post connections

Strings are secured at the top and bottom of the staircase through different connection methods depending on their position.

At the bottom, an outer string connects to the newel post using a mortise and tenon joint secured with dowels. This creates a strong structural connection that can withstand the forces generated during use.

At the top of the staircase, where the string meets the upper floor, it is hooked over the trimmer joist. This trimmer joist forms part of the floor structure and provides a solid fixing point.

Technical specifications

Typical dimensional requirements include:

• 100 × 100mm newel posts
• 75 × 50mm handrails
• 40 × 40mm balusters
• 250 × 50mm strings
• Housing depths of 12-15mm
• Optimum string pitch of 35°

Safety requirements and building regulations

Stair design must comply with specific safety requirements to ensure user protection.

Dimensional constraints

Building regulations specify maximum and minimum dimensions:

• Maximum rise per step: 220mm
• Minimum going per step: 220mm
• Maximum steps per flight: 16 steps
• Door clearance: Minimum 400mm clear space required for door swing

Design relationship

The relationship between rise (R) and going (G) must satisfy the formula:

$2R + G = 550-700mm$

This ensures a comfortable stride length and safe stepping pattern for users.

Design calculations

Stair design requires precise calculations to ensure compliance with building regulations whilst fitting the available space.

Calculation process

Step 1: Determine number of steps

• Measure the total rise between floors
• Divide by the maximum number of steps (16) to establish if this is feasible
• Adjust the number of steps to achieve a practical rise dimension

Step 2: Calculate going dimension

• Use the rise value in the formula $2R + G = 550-700mm$
• Solve for G to determine the going measurement
• Verify this meets minimum going requirements (220mm minimum)

Step 3: Check compliance

• Confirm the rise is 220mm or less
• Confirm the going is 220mm or more
• Ensure the $2R + G$ calculation falls within 550-700mm range