What is a Fall and Why is it Crucial for Balconies and Wet Areas?

Understanding falls (drainage slopes) is fundamental to proper water management in construction. Falls ensure water drains away from structures effectively, preventing damage, safety hazards, and maintenance problems. Whether you're building balconies, wet areas, or any horizontal surface exposed to water, proper falls are essential for long-term performance and safety.

This comprehensive guide covers falls in construction from basic principles through calculation methods and installation techniques, ensuring you understand why falls are crucial and how to implement them correctly.

Understanding Falls in Construction

What is a Fall?

A fall (also called slope, grade, or gradient) is the intentional slope given to horizontal surfaces to direct water flow toward drainage points. Falls are expressed as:

• Percentage: Rise over run × 100 (e.g., 2%)
• Ratio: Rise to run ratio (e.g., 1:50)
• Degrees: Angle of slope (e.g., 1.15°)
• Millimeters per meter: Direct measurement (e.g., 20mm/m)

Why Falls are Essential

Water management:

• Prevents ponding: Eliminates standing water
• Directs flow: Channels water to drainage points
• Reduces infiltration: Minimizes water penetration
• Protects structure: Prevents water damage

Safety benefits:

• Slip prevention: Reduces slip hazards from standing water
• Ice prevention: Prevents ice formation in cold climates
• Debris removal: Helps wash away debris
• Hygiene: Prevents stagnant water and bacterial growth

Structural protection:

• Prevents saturation: Keeps structural elements dry
• Reduces freeze damage: Prevents freeze-thaw damage
• Protects waterproofing: Reduces stress on waterproof membranes
• Extends lifespan: Increases structural lifespan

Building Code Requirements

Australian Standards

AS 3740 Waterproofing requirements:

• Minimum falls: 1:100 (1%) minimum for external areas
• Balcony falls: 1:80 (1.25%) minimum for balconies
• Shower falls: 1:80 (1.25%) minimum for shower floors
• Roof falls: Varies based on roof type and material

AS/NZS 3500.3 Plumbing and drainage:

• Surface drainage: Requirements for surface drainage
• Fall calculations: Methods for calculating proper falls
• Drainage capacity: Adequate drainage capacity requirements
• Installation standards: Standards for drainage installation

International Codes

International Building Code (IBC):

• Minimum slopes: 1/4 inch per foot (2%) minimum
• Balcony drainage: Specific balcony drainage requirements
• Accessibility: Requirements for accessible surfaces
• Safety standards: Safety requirements for sloped surfaces

European standards:

• EN 752: Drain and sewer systems outside buildings
• EN 12056: Gravity drainage systems inside buildings
• Minimum gradients: Specific gradient requirements
• Performance standards: Performance requirements for drainage

Types of Falls

Constant Fall

Single slope:

• Description: Uniform slope across entire surface
• Use: Simple rectangular areas
• Benefits: Easy to construct, predictable drainage
• Calculations: Single gradient calculation

Advantages:

• Simple construction: Easy to build and verify
• Predictable performance: Reliable water flow
• Easy maintenance: Simple to inspect and maintain
• Cost-effective: Lowest cost option

Multiple Falls

Four-way fall:

• Description: Surface slopes toward central drain
• Use: Large areas with central drainage
• Benefits: Efficient drainage, shorter water travel
• Calculations: More complex geometric calculations

Two-way fall:

• Description: Surface slopes toward two edges
• Use: Areas with drainage on two sides
• Benefits: Good drainage, flexibility in design
• Calculations: Coordinate two slope directions

Cricket and Valley Falls

Cricket construction:

• Description: Raised area directing water around obstacles
• Use: Around penetrations and equipment
• Benefits: Prevents water pooling around obstacles
• Construction: More complex forming and construction

Valley construction:

• Description: Depression directing water toward drains
• Use: Large roof areas and complex drainage
• Benefits: Efficient water collection
• Construction: Requires careful forming

Fall Calculations

Basic Calculations

Percentage calculation:

• Formula: Rise ÷ Run × 100 = Percentage
• Example: 25mm rise over 1000mm run = 2.5%
• Minimum: 1% minimum for most applications
• Typical: 2-3% for good drainage

Ratio calculation:

• Formula: 1:X where X = Run ÷ Rise
• Example: 1000mm run ÷ 25mm rise = 1:40
• Common ratios: 1:50, 1:80, 1:100
• Code minimums: Typically 1:100 minimum

Practical Applications

Balcony fall calculation:

• Width: Measure balcony width
• Minimum fall: Apply minimum code requirement
• Calculate drop: Width × fall percentage
• Example: 3m × 1.25% = 37.5mm total drop

Shower fall calculation:

• Distance to drain: Measure distance to drain point
• Minimum fall: Apply 1:80 minimum
• Calculate drop: Distance × fall ratio
• Example: 1200mm × 1:80 = 15mm drop

Complex Geometries

Curved surfaces:

• Radial falls: Falls radiating from center point
• Spiral falls: Continuous spiral drainage
• Complex calculations: May require professional design
• 3D modeling: Computer modeling for complex shapes

Multi-level falls:

• Stepped falls: Multiple level changes
• Terraced drainage: Terraced drainage systems
• Overflow systems: Primary and secondary drainage
• Emergency drainage: Backup drainage systems

Installation Techniques

Surface Preparation

Base preparation:

• Level base: Start with level base surface
• Screeding: Use screeds to establish fall
• Compaction: Proper compaction of base materials
• Accuracy: Maintain accuracy throughout

Forming systems:

• Screed boards: Temporary guides for fall
• Laser levels: Precision leveling systems
• String lines: Simple fall guides
• Template systems: Reusable forming systems

Concrete Installation

Pouring techniques:

• Consistent thickness: Maintain consistent slab thickness
• Fall maintenance: Maintain fall during pour
• Screeding: Screed to proper fall
• Finishing: Finish to maintain drainage

Quality control:

• Level checking: Regular level checking
• Fall verification: Verify fall accuracy
• Water testing: Test water flow
• Final inspection: Comprehensive final inspection

Membrane Installation

Substrate preparation:

• Smooth surface: Prepare smooth substrate
• Fall verification: Verify substrate falls
• Repair defects: Repair any defects
• Prime surface: Prime if required

Membrane application:

• Maintain falls: Maintain substrate falls
• Uniform thickness: Apply uniform membrane thickness
• Detail work: Carefully detail drainage areas
• Protection: Protect membrane during construction

Drainage Integration

Drain Placement

Drain location:

• Low points: Place drains at low points
• Accessibility: Ensure drain accessibility
• Capacity: Adequate drain capacity
• Maintenance: Easy maintenance access

Drain types:

• Floor drains: Standard floor drainage
• Linear drains: Linear drainage systems
• Channel drains: Channel drainage systems
• Overflow drains: Emergency overflow drainage

Collection Systems

Surface drainage:

• Sheet flow: Water flowing across surface
• Channel flow: Water flowing in channels
• Collection points: Strategic collection points
• Conveyance: Proper water conveyance

Subsurface drainage:

• Underdrain systems: Drainage below surface
• French drains: Gravel-based drainage
• Perforated pipes: Subsurface collection
• Sump systems: Water collection sumps

Testing and Verification

Construction Testing

Water testing:

• Flood testing: Test with standing water
• Flow testing: Test water flow patterns
• Drainage rate: Measure drainage rates
• Ponding check: Check for ponding areas

Survey verification:

• Laser measurement: Precise fall measurement
• Grid surveys: Comprehensive surface survey
• Spot checks: Random verification points
• As-built documentation: Document actual falls

Performance Monitoring

Long-term monitoring:

• Drainage performance: Monitor drainage performance
• Settlement monitoring: Monitor for settlement
• Maintenance needs: Identify maintenance needs
• System optimization: Optimize system performance

Problem identification:

• Ponding areas: Identify ponding problems
• Blockage issues: Identify drainage blockages
• Capacity issues: Identify capacity problems
• Structural issues: Identify structural problems

Common Problems and Solutions

Construction Problems

Common issues:

• Inadequate falls: Falls below code minimum
• Reverse falls: Falls sloping wrong direction
• Ponding areas: Areas where water ponds
• Poor workmanship: Inconsistent or poor construction

Solutions:

• Careful planning: Plan falls carefully
• Quality control: Implement quality control
• Regular checking: Regular fall verification
• Professional help: Use qualified professionals

Performance Problems

Common failures:

• Blocked drains: Drains blocked by debris
• Settlement: Settlement creating reverse falls
• Membrane failure: Waterproof membrane failure
• Structural movement: Movement affecting falls

Solutions:

• Regular maintenance: Regular cleaning and maintenance
• Prompt repair: Repair problems promptly
• Professional assessment: Professional problem analysis
• System upgrade: Upgrade inadequate systems

Maintenance Requirements

Regular Maintenance

Inspection tasks:

• Visual inspection: Regular visual inspection
• Water testing: Periodic water flow testing
• Drain cleaning: Regular drain cleaning
• Surface cleaning: Keep surfaces clean

Maintenance schedule:

• Monthly checks: Basic monthly inspections
• Seasonal maintenance: Comprehensive seasonal maintenance
• Annual inspection: Professional annual inspection
• Storm aftermath: Inspection after severe weather

Long-term Care

System monitoring:

• Performance tracking: Track drainage performance
• Settlement monitoring: Monitor for settlement
• Condition assessment: Regular condition assessment
• Upgrade planning: Plan system upgrades

Professional services:

• Professional inspection: Regular professional inspection
• Specialized testing: Specialized testing services
• System maintenance: Professional maintenance services
• Emergency response: Emergency repair services

The Bottom Line

Falls are a fundamental aspect of construction that directly impacts the safety, durability, and performance of buildings. Proper falls prevent water damage, reduce maintenance requirements, and ensure safe use of balconies and wet areas. Understanding and implementing proper falls is essential for any construction project.

Remember: Inadequate falls can lead to serious water damage, safety hazards, and expensive repairs. The cost of proper falls during construction is minimal compared to the cost of fixing drainage problems later.

The key to successful fall implementation is:

• Understand code requirements for your specific application
• Calculate falls properly using appropriate methods
• Install accurately with proper quality control
• Test thoroughly to verify performance
• Maintain regularly to ensure ongoing performance

Start with proper planning and calculation, then execute installation carefully with regular verification. Proper falls are an investment in the long-term performance and safety of your construction project.

Ready to complete your construction knowledge? Learn about The Importance of Site Cleanliness and Waste Management and discover A Guide to Building Contracts: What to Look For to round out your understanding of construction best practices.