Ground Floors: Construction and Insulation

Ground, First, and Intermediate Floors

• The topic of the session is ground, first, and intermediate floors
• Module Leader: Graham Terry
• Domestic floor construction types were discussed
• Issues with older floor construction methods were investigated
• 'U' values and calculation formulas were introduced

Learning Outcomes

• Appreciate different domestic floor constructions
• Investigate challenges of older floor designs
• Understand 'U' values and their calculation application

Topics for the Session

• Ground floors
• Functions and Stability
• Early timber floors
• Solid floors
• Suspended floors
• Insulation requirements

Ground Floors - Definition

• A horizontal surface supporting building occupants, furniture, equipment, and machinery.

Ground Floors - Functional Requirements

• Strength and stability
• Resistance to damp penetration
• Good thermal insulation
• Durability

Ground Floors (cont.)

• Classified as solid or suspended
• Solid floors gain support from the earth
• Suspended floors span between supports

Ground Floors (cont.)

• Construction materials:
  • Timber joist with timber floor
  • Concrete with sand and cement screed
  • Concrete with floating timber floor
  • Concrete beams & infill blocks & screed
  • Precast concrete floor panels with a screed

Early Timber Floors (1890s)

• Typical floor structure from the 1890s
• Joists built directly into walls
• Air vents (but damp-proof courses were rare)
• Void below floor
• Restricted ventilation
• Shallow foundations (if present)
• Ponding if earth is below external ground level
• Damp, dry-rot, and draughts were common issues

Early Timber Floors (1890s) (cont.)

• Most Victorian and Edwardian houses used suspended timber floors except kitchens and sculleries (solid flooring more common in these areas)
• Joists spaced 350-400mm apart on external & intermediate sleeper walls

Early Timber Floors (Cont.)

• Problems: Damp, dry rot, and draughts through plain-edged boards

Timber Floors (1930s)

• Improvements included concrete overslab support on honey-combed sleeper walls with damp-proof courses and numerous sleeved floor vents (along with T&G boards or boarding)

Timber Floors (1930s) (cont.)

• Damp-proof courses in main and sleeper walls
• Ventilation
• Joists supported on sleeper wall
• Square-edged or Tongue & Groove (t&g) boarding

Modern Timber Floors

• Raised timber floors are less common due to higher costs compared to ground bearing concrete counterparts

Stability of a Suspended Timber Floor

• Factors influencing stability:
  • Span
  • Carried load
  • Joist depth and thickness
  • Timber type
  • Joist spacing
  • Floor covering type and thickness
  • Strutting use and spacing

Early Concrete Floors (1890s)

• Common in Victorian and Edwardian houses' kitchens and sculleries, adopting ground bearing solid floors.
• Concrete overslab concrete between 100-125mm thick laid over prepared ground.

Early Concrete Floors (1890s-1930s)

• First type: Solid concrete slab floor – vulnerable to damp without hardcore.
• Progress to hardcore fill beneath the floor.

Solid Ground Floor Construction (1930s-1960s)

• Damp-proof membrane (DPM) often laid over the concrete slab. Many of these were cold-applied bitumen solutions.
• Thicker screeds needed if DPM on top of slab (e.g., 50mm).

Solid Ground Floor Construction (late 1960s-early 1990s)

• Polythene DPM lapped by DPC.
• Sand-cement screed (3:1) approximately 38mm thick.
• 100mm concrete slab laid on polythene DPM.
• Compacted hardcore underneath.

Construction Sequence

• Shows steps in ground floor construction

Modern Solid Ground Floor Construction

• Hardcore compacted, levelled, and blinded with sand to prevent damage to DPM.
• 38mm floor screed
• Insulation above the DPM

Modern Solid Ground Floor Construction (cont.)

• Chipboard or particle board laid on vapour control layer
• T&G (tongue and groove) for chipboard
• 10mm gap around perimeter for thermal and moisture expansion. Edge insulation not usually required.

Suspended Ground Floor (cont.)

• Supported by inner leaf of external walls and internal walls.
• Inverted 'T' beams (150-200mm deep) as factory-produced supports
• Concrete blocks are supported
• Ventilation of void is important
• Constructed to avoid organic materials

Precast Concrete Floor Panels

• Light weight (225mm depth) for depth same as standard blocks.
• High load bearing
• Up to 6 meters long and 1.2 meters wide

Why Suspended Ground Floors Are Used?

• Piled foundations unsuitable for ground-bearing slabs
• High water tables
• Aggressive ground chemicals (that attack hardcore/concrete)
• Large volumes of hardcore needing consolidation
• Sloping sites resulting in uneven hardcore depths

Damp Proof Membranes to Floors

• To prevent moisture rising (horizontal damp proofing in slab)
• Usually formed in polythene sheets
• Crucial that linked to exterior walls' dpc
• Failure to include can cause dampness

Screeds

• Used for providing a level base for floor finishes
• Thickness: 75mm when laid onto floor insulation
• Cement to sand ratio: 1:3 (cement to sharp sand)
• Cracking & curling occur with poor bond or thin screed
• Solid walkable surface
• Edge insulation required to prevent cold bridging

Screed Laying

• Screed laid onto concrete base
• Perimeter edge insulation visible

Thermal Insulation

• Main function: Reduce heat loss through the building's external fabric.
• Reduced heat input saves fuel and power.

Thermal Insulation (cont.)

• Building Regulations (Approved Document L) focuses on conservation of fuel and energy in dwellings greater than 30m² in floor space
• U-value represents the rate of heat flow through a material; the lower the value, the better the insulation performance
• Greatest heat losses from ground floors tend to be at perimeter, where heat transfer to the outside air is most likely.

Calculation of U-values

• U-value = 1 / Total thermal resistance (W/m²K)
• R-value (resistance) =Thickness of the Material/ Thermal Conductivity(W/m²K)

Thickness of Insulation

• Tables with values for various products (rockwool rockfloor), including thickness needed for specific U-values. Ground Bearing slab construction & Suspended beam and block construction

Insulation

• No distinct information on Insulation

What We Have Covered Today

• Types and developments in domestic flooring
• Selection criteria for appropriate flooring type(s) for various circumstances
• Introduction to U-values and their calculation formulas

Upper floors

• Next segment covering upper floors

Learning Outcomes (Upper Floors)

• Victorian floors
• Modern timber floors
• Floor joist sizes
• Openings, restraint, services
• Space joists, TJI joists
• Concrete floors
• Beam & block
• Hollow core
• Finishes
• Stair definitions

Victorian Floors

• Joist sizing: Span calculation in feet, then adding 2 inches for final dimension
• Span of 12 feet = 8 inch joists

Modern Timber Joists with a Timber Floor

• Most upper floors constructed using a series of timber joists. Rectangular shape, covered by chipboard or floorboards
• Joists are typically spaced at 400 ,450, or 600 mm

Modern Timber Joists with a Timber Floor (cont.)

• Why using timber: Readily available, relatively cheap, ease of work, fixings/repairs are straightforward

Use of Structural Timber

• Structural timber must meet stress-grading standards for suspended floors according to relevant Building Regulations (such as Approved Document A & TRADA Fact Sheet No. 3).
• The size and spacing of joists depend on load, span (length to be supported), and wood grade. Example data given re. size/span for various timber types.

Size of Floor Joists (Span Tables)

• Data tables show span support values for different joist sizes and loadings

Floor Joists Arrangement

• Joists typically spaced at 400mm centres
• Supports for partition, stairwell
• Blocking, Strapping, & Strutting for support

Restraining Floor Joists

• Restraint straps are required when joists run parallel to walls, every 2 metres
• Crossing 3 joists & needing noggings below
• Use with hangers/straps

Restraining Floor Joists (cont.)

• Joists nailed to hangers
• Strap use around gable walls & loadbearing walls

Openings in Timber Floors

• Joist trimming for widths (e.g., 75mm wide or possible 2 x 50mm joists) & bolting

Strutting

• Different methods for various span lengths:
  • Herringbone
  • Solid method
  • Patent Metal supports

Provision of Services

• Holes and notches for pipes/cables
• To Building Regulations standards & NHBC guidelines (minimum usage)

Modern Joists

• Metal web joists/space joists and 'I' beams are becoming common
• More accessible spacing and larger spans reduce loadbearing partition need.

Space Joists

• Consist of parallel stress-graded timber flanges joined by engineered, galvanised steel webs
• Webs attached to flanges with nail plates
• Available depths from 252mm to 418mm – matching solid joists

Standard Truss Joist (TJI)

• 'I'-shape cross-section
• Manufactured with uniform moisture content to prevent splitting/bowing/twisting
• Much lighter than other timber joists
• Available up to 20m in length
• More rigidity eliminating laps over beams and walls

Concrete Floors

• Commonly used in flats & maisonettes for sound/fire resistance
• Building Regulation Document E gives info on sound passage properties

Beam and Block Floors

• Concrete blocks are directly supported by timber battens for a concrete topping

Hollow Core Floors

• A 150mm thick floor can support spans up to 7m

Finishes

• Modern floors often covered with tongued & grooved (t&g) chipboard or floorboards.
• Alternative usage of varnished boards is possible
• Modern ceilings typically consist of plasterboard and plaster rendering

Sound and Fire (Floors)

• Specified sound insulation is needed for upper floors using Building Regulations (AD E)
• Suitable 100mm sound-proofing quilt is adequate between the joists & 15mm plasterboard
• More detailed provisions required in flats for issues such as impact and fire resistance (Document B).

Houses (Floors)

• The system consists of high-density mineral wool bonded to high-density tongue & grooved (t&g) cement particle board flooring. This is for improved construction and to eliminate potential cold bridges

Flats (Floors)

• Concrete plank floors are used in flats with fully grouted joints
• 18mm t&g (tongue and groove) chipboard on a 25 mm resilient layer
• 40mm concrete screed
• 15mm plasterboard ceiling/ Suspended ceiling.

Floor Details

• Illustrative, diagrammatic information on differing ground floor types (for reference)

This quiz covers essential aspects of ground, first, and intermediate floor construction. Participants will investigate different types of domestic floor constructions, the challenges posed by older designs, and the crucial 'U' values and their calculations. Enhance your understanding of floor stability, functionality, and insulation requirements.