Upper Floors Notes

Upper Floors

Regulations and Guidelines

  • Floors must provide strength and stability to withstand dead and live loads.
  • Durability is essential to withstand everyday use.
  • Ground floors require moisture resistance to prevent rising damp.
  • Thermal insulation is crucial to prevent heat loss and reduce heating costs.
  • NBS (National Building Specification) is a UK-based system used for construction specifications.
  • Robust Details are pre-tested constructions that exceed building regulation performance standards, eliminating the need for pre-completion sound testing.

Primary Functions of Floors

  1. Provide a level surface with sufficient strength.
  2. Reduce heat loss.
  3. Provide sound insulation.
  4. Provide fire resistance.

Types of Floors

  • Function: Domestic (small span) / Non-domestic
  • Location: Inside a flat (acoustic and fire considerations less important) / Between flats
  • Properties: Fire-resistant, insulated, heated
  • Materials:
    • Timber.
    • I-beam joist.
    • Metal web joist.
    • Concrete (slab, beam and block, plank, precast).
    • Earth, brick, glass.
    • CLT.
  • Finishes: Terrazzo, stone, carpet.

Joists

  • Joists are typically made of softwood, with common dimensions being 50mm wide and varying depths (e.g., 175mm, 200mm, 225mm).
  • Maximum span is typically 7500mm (BS5268).
  • Spacing is typically 400mm, but 450mm or 600mm spacing is also possible.
  • Straps can be used to provide restraint where joists run parallel to internal walls.
  • Timber blocking between joists provides rigidity.
  • Correctly sized beams will suffer minimal deflection (BS EN 338).
  • If joists are not deep enough, they will bend; if they are not wide enough, they will twist.

Strutting

  • Strutting is used to brace or strengthen a framework by resisting longitudinal compression.
  • Herringbone strutting and solid strutting are common types.
  • Strutting provides load transfer to adjacent members and lateral support to joists to avoid instability.
  • Herringbone strutting is said to reduce the effect of vibrations.
  • Solid strutting should be at least 38 mm thick timber extending to at least three quarters the joist depth.
  • Herringbone strutting should be at least 38 x 38mm timber and can only be used where the spacing between the joists is less than three times the depth of the joist.

Slab and Joist System

  • Consists of a slab spanning between beams and usually an intermediate joist in one direction.
  • Slab thickness between the joists is often controlled by fire-resistance requirements.
  • Joists can be built into the wall if any gaps around them are sealed to prevent air leakage.

Historical Construction Details

  • Late 19th Century:
    • Typical upper floors constructed from 8" by 2" (200 x 50mm) softwood floor joists fixed at 12" to 16" centres (300 to 400 mm).
    • Joists were usually built into the walls; corbels were sometimes used for better sound and fire protection.
    • Floors covered with square-edged softwood boards and finished with lath and plaster ceiling.
  • 1930s:
    • Construction was similar, with requirements for joists to rest upon a wall plate or steel bearing bar.
    • Joist ends were often tarred or creosoted where built into walls.
  • 1950s and 1960s:
    • System-built houses used steel joists; traditional upper floors were common with 'stretched' centres and reduced joist sizes to save timber.
    • Boarded ceilings replaced lath and plaster with fibreboard, asbestos board, and plasterboard.

Modern Floors - Domestic

  • Modern upper floors differ from 1950s floors as they require strapping to restrain external walls, joist hangers, and chipboard or strand board instead of floorboards.
  • Ceilings are typically plasterboard.
  • Timber joists should be sized according to span and loads.
  • Joists should be supported on restraint-type joist hangers where they are supported by external walls.
  • Lateral restraint straps should be provided at 1,800mm centres and fixed to noggings and floor joists.
  • Decking should be flooring grade and at least 15kg/m215kg/m^2 for sound resistance.
  • Plasterboard ceiling should be at least 10kg/m210kg/m^2 for sound resistance.
  • Sound insulation should be at least 100mm fibreglass or similar.

Timber Floor Construction Points

  • Floors provide lateral restraint to walls; straps are needed where joists run parallel to the wall, positioned every 2m (up to 3m is acceptable for stairwells).
  • Galvanised mild steel straps must have a minimum cross-sectional area of 30 x 5mm.

Modern Joists

  • Wooden I-Beam joists.

Concrete Floors

One-Way System
  • Spans across parallel lines of support provided by walls and/or beams.
Two-Way System

  • Spans supports running in both directions.

  • For B/A > 2, design as one-way slab.

  • Economic spans vary based on the type of slab.
    Continuous reinforcement ratio span to depth:

  • Concrete slab: 32:1

  • Coffered slab: 26:1

  • Steel space frame: 15:1

Systems of Concrete Floors:

  • Beam and block.
  • Thermal beam and block.
  • Beam and hollow blocks.
  • Precast concrete planks (solid and hollow).
  • Metal decking.
  • Concrete slabs.
Beam and Block
  • Inverted ‘T’ beams.
  • Designed for housing markets, both ground and upper floors.
  • Complies to BS8110 “The Structural use of Concrete”.
Thermal Beam and Block
  • ‘U’ value as low as 0.15W/m2K0.15 W/m^2K.
In-Situ Hollow Block Floors
  • Lighter than solid slab floors and result in a flat soffit.
Beam and Hollow Block
  • Hollow tiles made of clay or concrete are placed between tie-beams and covered with concrete.
Flat Plate Floor
  • In-situ floor comprises a solid reinforced slab bearing on concrete columns.
  • Allows flexibility for locating horizontal services above a suspended ceiling.
Solid Concrete Slab Floor
  • Floor covering.
  • Screed with underfloor heating.
  • Separating layer.
  • Impact sound Insulation.
  • In situ solid concrete slab.
Metal Decking Composite Floors
  • Commonly used in conjunction with composite beams.
  • Stud connectors are typically welded through the deck.
Advantages of Composite Beams
  • Bending resistance increased by a factor of 1.5 to 2.5.
  • Stiffness increased by a factor of 3 to 4.5.
  • Steel weight reduced by typically 30 to 50%.
  • Reduction in beam depth (span:depth = 25).
In-Situ T-Beam Floors
  • Involve casting a series of parallel, reinforced T-beams at the same time as the slab.
Ribbed (Waffle) Slab
  • Ribbed floors are either one-way spanning (ribbed slab) or two-way (waffle slab).
Pre-Cast Concrete Planks
  • Solid and Hollowcore planks are used in offices, shops, light industrial, and residential properties.
Precast Floors
  • Require no shuttering, save site work and time, reduce waste.
Pre-Tensioned Planks
  • Supported on loadbearing walls or beams, laid to form a continuous shuttering and working platform.
Voided Biaxial Slabs
  • Reduce the amount of concrete.
Advantages:
  • Design Freedom.
  • Reduced Dead Weight.
  • Longer spans between columns.
Lattice Girder
  • System that serves as an alternative to conventional concrete-in-place floors.
One-Way Concrete Slab & Beam Floor System

Properties of Floors, Special Floors & Flooring

  • Floors consist of a subfloor for support and a floor covering.
  • Subfloor provides support, acoustic and fire insulation, and houses wiring, plumbing, and other services.

Acoustics

Ways of controlling noise:

a) Installing a resilient layer between the structural floor and a hard-finish floor will help cushion impacts
b1) Acoustic insulation in the structural zone
b2) or creating a solid structural zone
c) Insulation (76-152mm thick) attached to the underside of the floor
d) Suspend the ceiling and use an absorber in the resulting cavity

Separating Floor - Concrete

  • Precast concrete plank
  • Screed laid on InstaCoustic InstaLay 65 resilient layer

Timber frame walls only: Timber I-Joists; Finnforest SoundBar Systems
Min 300mm from top of beam to ceiling board

Underlayment

Reasons why underlay hould be used with wooden and laminate flooring:

  • Effective underlay helps to cushion the flooring. This makes it more comfortable to walk on.
  • It reduces the noise created by walking on wooden boards (reduction of up to 50%)
  • Thermal insulation
  • Protecting flooring from wear and tear.

Floating Floors

  • A floor that does not need to be nailed or glued to the subfloor.

Nightingale Floor

  • Floor designed to make chirping sound when walked upon

Sports Floor

  • Sprung flooring enhances sports or dance performance

Raised Flooring

  • A type of floor that provide an elevated structural floor above a solid substrate (often a concrete slab) to create a hidden void for the passage of mechanical and electrical services.

Flooring

Materials_
  • Wood / Laminate Flooring
  • Tiles
  • Stone
  • Terrazzo
  • Carpet
  • Area Rugs
  • Resilient flooring: linoleum or vinyl flooring
Wood Flooring
  • Any product manufactured from timber that is designed for use as flooring
Laminate Flooring
  • A multi-layer synthetic flooring product fused together with a lamination process