Moisture-Compensating Returned Stair Tread Joint
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Solution Overview
Problem
Existing returned stair treads tend to gap or deform due to changes in ambient temperature and humidity, particularly when exposed to moisture, leading to unsightly gaps and potential safety issues, especially when overlaid on OSB or plywood staircases.
Innovation Solution
A thin returned stair tread assembly with a tongue-and-groove connection between the stair tread plate and return nosing, secured by adhesive and mechanical fasteners, allowing for sliding movement to accommodate expansion and contraction while maintaining the joint integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the return nosing is glued to the side edge of the tread member along the entire width, then the joint is securely attached, but the joint gaps open when the tread expands due to moisture absorption
Solution Approach 1:
The continuous glue line is segmented into discrete attachment points (nails or screws at specific intervals). This segmentation allows the joint to remain secure at fixed points while permitting controlled movement and expansion between the attachment points, preventing gap formation as the wood expands with moisture absorption.
Solution Approach 2:
The joint transitions from a static, fully rigid connection (continuous glue) to a dynamic connection that allows controlled movement. The spaced fasteners create a joint that can flex and accommodate dimensional changes in the wood while maintaining overall structural integrity, adapting to environmental moisture variations.
2Shape
If a standard thickness wooden tread is used over OSB, then the wooden appearance is achieved, but the combined thickness exceeds building code requirements
Solution Approach 1:
A thin wooden veneer or thin wood tread is used instead of a thick solid wood tread. This thin layer provides the desired genuine wooden appearance while minimizing thickness addition. The thin film approach allows the replacement tread to meet building code thickness requirements while still achieving the aesthetic goal of a real wood surface.
3Shape
If the staircase is completely replaced with genuine wood, then the aesthetic appearance is improved, but the project becomes expensive and time-consuming
Solution Approach 1:
Instead of replacing the entire staircase structure, a thin wooden veneer is applied to the existing OSB or plywood treads. This copying approach replicates the appearance of genuine wood without requiring complete demolition and reconstruction, significantly reducing project time and cost while achieving the desired aesthetic transformation.
Solution Approach 2:
The thin wooden tread assembly serves multiple functions: it provides the aesthetic appearance of genuine wood, maintains compliance with building code thickness requirements, and can be installed over existing structured treads (OSB, plywood). This multi-functional solution eliminates the need for complete staircase replacement while achieving both cosmetic and structural requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Prevents significant gapping or deformation of the exposed joint, ensuring durability and aesthetic appeal even under varying temperature and humidity conditions, suitable for retrofitting over existing OSB or plywood staircases without altering the staircase's thickness or appearance.
Implementation Method 1
The side tongue is disposed in the side groove and slidably connect the stair tread plate and the return nosing
Implementation Method 2
The return nosing is secured to the front nosing and the stair tread plate only along a region including the exposed joint
Data Source
AI summary
A returned stair tread assembly comprises a tread plate, a front nosing and a return nosing fitted flush against each other to form an exposed joint between the front and return nosings, and a device for securing the return nosing to the front nosing and the stair tread plate. The tread plate has a side tongue. The front nosing has a front nosing tongue spaced from a forward end of a side edge surface of the front nosing. The return nosing receiving the front nosing tongue of the front nosing and the side tongue of the stair tread plate therein. A front end of the side groove is spaced from a forward end of the return nosing. The front nosing tongue and the side tongue are disposed in the side groove and configured to slidably connect the stair tread plate and the return nosing.