Flat Roofs

Flat roofs, serve a dual function as both a roof and a ceiling. They belong to one of the two main types of roof constructions, perfectly suited to modern architecture. Flat roofs require specific waterproofing and thermal insulation systems, with proper drainage through roof inlets being a key element. Despite their name, flat roofs always have a slight slope—at least 2 degrees—to ensure effective rainwater runoff.

In single-family housing, flat roofs are typically constructed from reinforced concrete load-bearing slabs. Depending on the layer arrangement, we distinguish traditional and inverted flat roof systems.

Layer Arrangement in a Flat Roof

A flat roof consists of multiple layers designed to create a watertight seal, prevent vapor penetration from the interior, and protect against moisture and water ingress. A well-structured layering system provides continuous insulation, ensuring waterproofing and vapor protection. Additionally, proper layering of thermal insulation eliminates thermal bridges.

The basic flat roof layers include:

• Load-bearing structure
• Vapor barrier
• Thermal insulation
• Slope-forming layer
• Waterproofing layer

The waterproofing layer is the final protective barrier that shields the structure and interior from moisture and leaks. A well-designed flat roof system ensures effective protection against weather conditions, moisture, and heat loss.

Load-Bearing Structure

The structural base of a flat roof can be made of reinforced concrete, trapezoidal metal sheets, or wood. The main purpose of this load-bearing structure is to support the roofing layers.

Key factors when choosing a load-bearing structure:

• Expected loads (e.g., snow, heavy rainfall)
• Roof usage and surface area
• Thermal insulation requirements

Choosing the right structural base directly affects the thermal performance of the entire flat roof system.

Vapor Barrier

The vapor barrier in a flat roof prevents moisture penetration from interior spaces and attic areas. To ensure airtightness, it must be properly joined with the main roofing membrane.

Common vapor barrier materials:

• Standard bituminous membranes
• 0.20 mm vapor barrier films

A well-installed vapor barrier is essential for maintaining the integrity of the roof and preventing moisture damage.

Thermal Insulation

Thermal insulation plays a critical role in achieving the required thermal transmittance (U-value) as defined in Technical Building Regulations (WT 2021).

Common thermal insulation materials:

• EPS 100 Styrofoam
• XPS extruded polystyrene
• PIR insulation boards (higher fire resistance than styrofoam)

Properly designed thermal insulation ensures energy efficiency, prevents condensation, and extends the roof’s lifespan.

Slope-Forming Layer

The slope-forming layer ensures proper rainwater runoff and prevents water accumulation. It can be formed using:

• EPS 100 Styrofoam slope boards (suitable for various structures)
• Concrete slopes (primarily for reinforced concrete structures)

A well-executed slope-forming layer ensures effective drainage and enhances thermal insulation longevity

Waterproofing Layer

The waterproofing layer is the most critical component in protecting a flat roof against moisture and water infiltration. Proper material selection and precise installation are key to long-term performance.

Types of Flat Roof Waterproofing

1. Bitumen Sheets & Membranes
   • Can be mechanically fastened or adhered.
   • Require precise installation to ensure durability.
   • Fastening density is crucial, especially along roof edges.
   • Includes two layers: base and top waterproofing sheets, which are either welded or glued.
2. Liquid Waterproofing Membranes
   • Applied using rollers or spray equipment.
   • Creates a seamless, watertight surface.
3. Modern Polymer-Bitumen Membranes
   • Composed of durable reinforcement layers combined with polymer-modified bitumen.
   • Enhanced with elastomers and polymers.
   • Offers high durability and flexibility.
4. PVC, TPO/FPO & EPDM Roofing Membranes
   • Three-layer structure:
     • Top layer: UV & chemical-resistant.
     • Middle layer: Reinforcement for mechanical strength.
     • Bottom layer: Ensures strong adhesion.
   • Designed to withstand UV exposure, temperature changes, and industrial gases.

Choosing the right waterproofing system and ensuring precise application guarantees long-lasting protection against water damage and extends the roof’s lifespan.