Introduction to Timber Framing Systems

Principles and Design of Construction for Stairs

• Definition of a Stair: A stair is a form of steps suitably arranged for the purpose of connecting different floors of a building. It serves as a primary means of vertical communication.
• Staircase and Stair Well: The enclosure containing the complete stairway is termed a staircase or a stair well.
• Structural Materials: Stairs can be constructed using several materials, including:
  • Timber
  • Stones
  • Bricks
  • Steel
  • Plain concrete
  • Reinforced concrete

Location and Placement of Stairs

• Safety and Egress: The location of stairs requires careful consideration because, in the event of fire or similar calamities, they often provide the only means of escape.
• Public Buildings: Stairs should typically be located near the main entrance.
• Residential Buildings: Stairs are often centrally placed to provide easy access from all rooms while maintaining privacy.
• Functional Requirements: Placement should ensure sufficient light and ventilation within the stairway.

Technical Terminology and Definitions

• Tread: The horizontal upper part of a step on which the foot is placed when ascending or descending a stairway.
• Riser: The vertical portion of a step that provides support to the tread.
• Flight: A series of steps without any platform, break, or landing in their direction.
• Landing: A horizontal platform that provides a break in a flight or series of steps.
• Nosing: The outer projecting edge of a tread, provided to give an architectural effect and make the staircase easier to negotiate.
• Line of Nosing: An imaginary line touching the nosing of each tread, running parallel to the slope of the stair.
• Pitch or Slope: The angle that the line of nosing makes with the horizontal.
• String or Stringers: The sloping members at the sides or middle that provide structural support for the steps.
• Handrails: Members provided at the edges of the flight to assist users in negotiating the stairway.
• Baluster: A vertical member made of wood, metal, or masonry that supports a handrail.
• Newel: A post forming the junction of flights with landings or carrying the lower end of the strings.
• Headroom or Headway: The clear vertical distance between the tread of a step and the soffit of the flight, ceiling, or beam immediately above it.

Requirements for an Effective Stair Design

• Width of Stair: Varies based on use and traffic volume.
  • Public Buildings: Usually $1.3-1.4\,m$.
  • Residential Buildings: Approximately $900\,mm$.
  • Minimum for Domestic Stairs: $865\,mm$ is accepted, with $800\,mm$ as the absolute minimum.
  • Disabled Access: Should not be less than $900\,mm$ wide.
  • Two-Person Passage: Requires a width between $1015-1065\,mm$.
• Length of Flight: For comfortable ascent, the number of steps in a single flight should be between $12-16$.
• Pitch and Slope: The slope should generally never exceed $40^{\circ}$ and should not be flatter than $25^{\circ}$.
• Headroom: The distance should not be less than $2.14\,m$.
• Step Proportions: Rise and tread dimensions must be uniform throughout the stair to permit regular movement.
• Thumb Rule for Dimensions:
  • $(Tread\,mm) + 2 \times (Rise\,mm) = 550-650\,mm$
• Standard Sizes:
  • Residential Step: Approximately $250 \times 160\,mm$.
  • Public Building Step: Range from $270 \times 150\,mm$ to $300 \times 130\,mm$.
• Landings: The length and width of landings should be at least equal to the width of the flight.
• Handrail Height: Placed at $900$ to $1000\,mm$ vertically from the line of nosing to the top of the rail.

Classification and Types of Stairs

• Straight Stair: Rises from floor to floor in one direction, with or without intermediate landings.
• Dog-legged Stair (Half Turn): Rises to a landing between floors, turns through $180^{\circ}$, and rises parallel to the lower flight to the floor above.
• Quarter Turn Stair: Rises to a landing between floors, turns through $90^{\circ}$ and rises to the floor above.
• Bifurcated Stair: Arranged with a wide flight at the start that sub-divides into two narrower flights at a mid-landing.
• Geometrical Stairs: These have no newels; the strings and handrails are continuous from floor to floor around a well. They may be rectangular, circular, or elliptical in plan with tapered steps.
• Newel Stair: Timber stairs using vertical posts (newels) at the end of flights to support strings and handrails. In concrete or steel, circular stairs may have a central newel from which treads radiate.
• Spiral/Helical Stair: Treads taper to a central vertical support. It is the most economical in terms of floor area but can be difficult or dangerous for children and those with limited mobility due to the sharp taper.

Timber Stair Construction Specifics

• Common Usage: Mainly used in domestic buildings with either closed or open risers.
• Standardization: In developed countries, these are often prefabricated by joinery firms.
• Stringer Types:
  • Cut String: The upper surface is cut to receive treads and risers; the lower edge is parallel to the pitch.
  • Closed or Housed String: The top and bottom edges are parallel to the slope. Grooves ($13\,mm$ deep housings) are cut into the insides to receive treads and risers, often secured with wedges and glue blocks.
• Joinery Details:
  • Handrails may be secured by draw-pinned tenon joints.
  • Newels may be notched for landing trimmers.
  • Treads are typically $25-38\,mm$ thick.
  • Risers are typically $10-12\,mm$ thick.

Principles and Functions of Doors

• Definition: A door is a screen used to seal an opening into a building or between rooms. It is a framework of wood, steel, aluminum, glass, or a combination of these, secured in a wall opening.
• External Doors: Used for interior access and security. Must be weather-resistant (thickness, stability, durability) and provide thermal/sound insulation.
• Internal Doors: Used for internal walls, partitions, and cupboards. Generally thinner as weather protection is unnecessary.
• Performance Requirements:
  • Fire Resistance: Designed to resist fire spread for at least $30$ minutes.
  • Privacy: Opaque materials prevent vision in bedrooms/bathrooms. Soundproofing provides oral privacy.
  • Aesthetics: Special doors use expensive, durable materials for visual effect.

Door Design and Sizing

• Location: Doors should be located near room corners (approx. $200\,mm$ from the corner) for space utilization. The number of doors should be minimized to avoid obstruction.
• Standard Sizes:
  • External Door: $875 \times 45 \times 2000\,mm$
  • Internal Door: $750 \times 40 \times 2000\,mm$
  • Bath/WC: $700 \times 40 \times 2000\,mm$
  • Public Buildings: $1200 \times 2000\,mm$
  • Hospital/Library: $1200 \times 2100\,mm$
  • Garage: $2500 \times 2200\,mm$

Classification and Mechanical Operation of Doors

• Side Hung Doors: Can be outward or inward opening, double door, or single/double swing.
• Sliding Doors: Straight run top-hung (single leaf), double leaf, or sliding/folding door.
• Industrial Doors: Straight sliding or sliding folding, often top-hung with bottom guides or rollers.
• Specialized Types:
  • Flexible Doors: For users with occupied hands (e.g., pushing trolleys).
  • Automatic Doors: Triggered by sensing and timing devices via a motor gear.
  • Others: Collapsible steel doors, rolling shutters, and revolving doors.
• Door Frames: Fixed inside wall openings with rebates $12-13\,mm$ deep. Frames are secured with galvanized steel cramps screwed to the back of the jamb.

Construction Types of Timber Doors

• Battened and Ledged: Simplest form for narrow openings (WC/Bathrooms); uses horizontal ledges ($75-100\,mm$ wide, $20-30\,mm$ thick) fixed to tongued and grooved boards.
• Battened, Ledged and Braced: Features braces that incline downward toward the side where the door is hung to prevent sagging.
• Framed, Battened, Ledged and Braced: Superior strength and durability; suitable for external use and rough handling.
• Panelled Doors: Made with timber, plywood ($10\,mm$ thick), or glazing fixed into stiles and rails.
• Flush Doors:
  • Solid Core: Timber strips, chipboard, or fiberboard strips glued together with plywood facings. High surface stability and acoustic resistance.
  • Semi-Solid (Skeleton) Core: Structural core of small section timbers (stiles, rails, intermediate rails) with plywood facing.
  • Cellular Core: Light softwood frame with fiberboard or paper core. Used for light-duty internal domestic applications; offers poor acoustic privacy and fire resistance.

Ironmongery for Doors and Windows

• Hinges:
  • Butt Hinges: Most common, recessed into frame and door.
  • Rising Butts: Lift the door as it opens to clear carpets; provides self-closing action.
  • Tee Hinges: Used for heavy ledged doors.
  • Lift-off Butt (Pin): Allows door removal without unscrewing; used for pre-hung doors.
  • Parliament Hinge: Projects from the frame to let a door fold back $180^{\circ}$.
• Bolts: Barrel bolts (surface fixed), Lever bolts (recessed), Cremorne bolts (top and bottom fixing via one handle), and Panic bolts.
• Closers: Hydraulic checks (surface or closing-face fixing), and concealed closers (Perko/Perkomatic types fitted into door thickness).
• Selectors: Used for pairs of rebated doors to ensure leaves close in the correct order.

Design and Function of Windows

• Definition: An opening in a wall for daylight, vision, and ventilation.
• Selection Criteria: Room size/utility, wind speed/direction, humidity, temperature, and architectural treatment.
• Design Considerations:
  • Northern side windows provide maximum daylight without glare.
  • Humid regions require cross ventilation past occupants.
  • Windows must be burglar-proofed for security.
• Safety in Tall Buildings: Code of Practice 153 recommends fittings for windows above the third story limit initial opening to $100\,mm$ and prevent slamming in high winds.

Window Classifications and Materials

• Hinged (Casement): Side, top, or bottom hung. May include a "dead light" or "fixed light" that does not open.
• Pivoted: Horizontally or vertically pivoted. Advantageous because the weight of frame and glass is balanced over central pivots.
• Sliding: Vertically or horizontally sliding.
• Composite Action: Acts like side/top/bottom hung for ventilation but can slide in frame grooves on hinged side stays.
• Sliding Folding: Sashes hinge to each other and fold; sashes run on pivoted wheels in overhead tracks.
• Materials:
  • Timber: Tropical hardwoods (e.g., Odum, which requires no paint).
  • Metal: Steel (needs corrosion protection) and Aluminum (lightweight, no protection needed).
  • uPVC: Unplasticated polyvinyl chloride.

Shading and Protective Devices

• Tropical Considerations: Elevated shading is required for indoor comfort.
• Fixed Devices: Vertical fins, horizontal fins (solid or tilted), and "egg-crate" combinations (fixed vertical and horizontal fins forming a perforated curtain wall).
• Movable Devices: Can be moved via pivots manually, automatically as the sun moves, or electronically.
• Window Fixing Methods:
  • Built-in: Construction of the wall occurs around the window; ensures a good fit and solid security.
  • Fix-in: Window is fitted into a pre-constructed opening with extra clearance; secured using L-shaped galvanized steel cramps.