Ground floors

CONSTRUCTION TECHNOLOGY (COTE 12153)

DOMESTIC FLOOR CONSTRUCTION FUNCTIONS OF GROUND FLOOR AND SELECTION CRITERIA

Introduction

• Ground floors for dwellings can take various forms based on:

  • Nature of the site

  • Quality of construction

  • Required speed of erection of the building

• All design solutions fulfill the same functional requirements.

• Ground floors can be categorized into two basic groups:

  • Suspended Floors: Structural elements span between supports without relying on the ground for support, creating a void beneath.

  • Ground-Supported (Solid) Floors: The underside of the floor is continuously in contact with and supported by the ground.

Functional Requirements

• The main function of the ground floor is to provide a safe and stable platform for activities within the dwelling.

• Additional functional aspects include:

  • Compliance with user needs and Building Regulations.

  • Factors influencing construction selection include performance aspects and site characteristics.

Generic Performance or Functional Requirements

1. Structural Stability

   • Must support dead loads and live loads without deformation or risk of structural failure.

   • For ground-supported floors, effective load dissipation relies on continuous ground contact.

   • For suspended floors, load transfer mechanisms rely on supporting structural elements (e.g., dwarf or sleeper walls).

2. Thermal Insulation

   • Ground floors must resist heat passage, varying needs for insulation based on floor type.

   • Solid Floors: Ground contact creates a protective zone at the floor's core, reducing heat loss from the building to the ground.

   • Suspended Floors: Voids beneath allow uniform heat transfer, necessitating insulation across the entire floor area.

   • Insulation levels need to account for specific heat loss areas, especially at the perimeter near external walls.

3. Exclusion of Ground Water and Contaminants

   • Prevent moisture ingress to the building as per Part C of Building Regulations; ground water poses significant risk.

   • Mechanism of Moisture Ingress: Capillary action can draw moisture through porous materials like concrete.

   • Capillarity: The tendency of water to move through porous materials due to surface characteristics.

   • Design details must counteract moisture ingress; impervious materials or capillary breaks are often essential.

   • Positive pressure from groundwater can exacerbate moisture issues in specific conditions (e.g., cellars, sloping sites).

4. Durability

   • Materials must withstand harsh environments for longevity.

5. Provision of Appropriate Surface Finish

   • Ground floors must have a level and smooth finish to allow for decorative coverings and ensure safety.

   • Minor surface irregularities can lead to wear and trip hazards; finishing methods include screeds or power floating.

Factors Affecting the Selection of Ground Floors

• Considerations when selecting ground floor alternatives include:

  • General construction form

  • Site nature

  • Anticipated loadings

  • Surface finish requirements

  • Cost

Considerations and Questions

• What advantages does having a void below the ground floor offer?

• Reasons for choosing a suspended floor over a ground-supported floor?

GROUND SUPPORTED FLOOR / SOLID FLOOR

Introduction

• Ground-supported floors are in continuous contact with the ground, transferring loads through this area.

• Often called ‘solid floors’, these floors lack voids or hollow areas within their construction.

• Numerous forms exist, but all meet the same performance requirements with limited flexibility in generic form.

Solid Floor Construction

1. Insitu Concrete Bed

   • Purpose: Main structural element providing a durable, level surface for loads from structure, furniture, and occupants.

   • Considerations:

     • Proper mix design and compaction are critical for strength.

     • Adequate thickness based on structural and load-bearing requirements.

     • Smooth finish for desired floor surface.

2. Mild Steel or Mesh Reinforcement

   • Purpose: Enhances tensile strength, prevents cracking, improves load distribution; placed uniformly throughout the concrete.

   • Considerations:

     • Follow engineering specs for type, size, and spacing of reinforcement.

     • Ensure rust protection for longevity.

3. Damp Proof Membrane (DPM) / Asphalt

   • Purpose: Prevent ground moisture affecting structural integrity.

   • Considerations:

     • Effective moisture barrier installation practice.

     • Compatibility with construction materials must be verified.

4. Sand Blinding

   • Purpose: Provides a smooth surface for placing insulation and concrete; laid over DPM or compacted earth.

   • Considerations:

     • Ensuring a uniform thickness is important for level surface quality.

5. Hardcore

   • Purpose: A compacted layer of coarse material providing stable base, aiding drainage, preventing ground movement.

   • Considerations:

     • Properly compacted to achieve density.

     • Thickness/specifications based on engineering needs.

6. Compacted Backfilled Earth

   • Purpose: Supports foundation and walls, minimizes settlement.

   • Considerations:

     • Ensuring appropriate compaction and backfilling techniques to prevent voids.

7. Insulation

   • Purpose: Enhances thermal performance for energy efficiency and comfort.

   • Considerations:

     • Thickness/type based on thermal needs and compatibility with other materials.

Characteristics and Structure

• Components Layering:

  • Plain concrete slab → Hardcore (stone) → Screed → Sand blinding → Asphalt → DPM → DPM

  • Various DPM positions may lead to efficient design solutions.

Insulation Guidelines

• Necessary for reducing heat loss; U-values of approximately $0.25 ext{ W/m}^2 ext{K}$ needed for compliance with regulations.

• Commonly shares thermal loss concentration at perimeter areas; cold bridging must be considered.

SUSPENDED FLOORS

Introduction

• Suspended floors arise in cases where a ground-supported option is unsuitable, particularly avoiding 'wet trades'.

• They create void beneath the floor and are increasingly constructed from precast concrete units.

Timber Ground Floors

• Traditionally seen as aesthetically pleasing, though costs persist as a discouraging factor for builders.

• Provides warmth and flexibility and allows utility installations easily via the below void.

Ventilation and Moisture Considerations

• Older constructions used direct joist contact with external walls, increasing moisture risk.

• Modern practices involve supporting joists on sleeper walls to enhance ventilation and moisture resistance.

Beam and Block Floors

• Description: Comprised of reinforced beams spaced closely (typically $600 ext{ mm}$), supporting infill blocks, with a sand/cement screed finish.

• Advantages: Allow easy on-site manipulation of units, reducing the need for extensive excavation and improving moisture management.

• Requirements: Always require DPM beneath to enhance moisture protection.

Summary of Advantages/Disadvantages

Solid Floors

Advantages:

1. Strength and Stability

2. Thermal Mass Contribution

3. Sound Insulation

4. Durability

5. Fire Resistance

Disadvantages:

1. Limited Flexibility

2. Complexity in Construction

3. Moisture Issues

4. High Weight Constraints

Suspended Floors

Advantages:

1. Versatile Design Configurations

2. Optimized Space Utilization

3. Quicker Installation Process

4. Enhanced Moisture Protection

Disadvantages:

1. Higher Sound Transmission

2. Potential Structural Deflections

3. Accessibility Limitations

4. Specific Cost Concerns

References

• Riley, M. and Cotgrave, A. (2018) Construction technology. Fourth edition. London: Palgrave.