Bituminous Coverings for Flat Roofs: Selection and Installation Technologies

Bituminous coverings are one of the oldest and most reliable solutions for covering flat roofs. Over decades, technology has improved significantly: from simple oxidised bituminous coverings to modern SBS and APP modified polymer-bituminous membranes. Today bituminous coverings hold one of the largest market shares due to reliability, resistance to Lithuanian climate conditions and good price-quality ratio.

This article details bituminous covering types, their layers, installation technologies, prices in Lithuania 2026 and proper selection guidelines for various building types.

Bituminous covering types

Oxidised bituminous coverings

The most traditional type. Bitumen is thermally treated by adding oxygen, which increases hardness and temperature resistance:

• Most economical option (10–18 EUR/m² materials)
• Service life 10–15 years
• Suitable for short-term solutions and warehouses
• Most often used as the bottom layer
• Lower elasticity in cold temperatures

SBS-modified bituminous coverings

SBS (Styrene-Butadiene-Styrene) is a polymer additive that makes bitumen elastic even at cold temperatures. The most popular choice in Lithuania:

• Maintains elasticity to -40°C
• Mechanical impact resistant
• Service life 25–30 years
• Suitable for both bottom and top layers
• Price: 18–28 EUR/m² materials

APP-modified bituminous coverings

APP (Atactic Polypropylene) additive provides high heat and UV resistance:

• Resistant to temperatures up to +120°C
• Good UV resistance
• Suitable for southern climates but works in Lithuania
• Service life 25–30 years
• Price: 20–30 EUR/m² materials

Self-adhesive bituminous coverings

Modern self-adhesive membranes have a special adhesive layer for flameless installation:

• Renovation work
• Indoor zones
• Sites with fire risk
• Quick installation
• Price: 22–35 EUR/m²

Bituminous covering layer structure

Modern bituminous covering is a multilayer membrane, each layer with specific function:

1. Protective layer (top): mineral granules or aluminium foil, UV and mechanical damage resistant
2. Top bitumen layer: 1.5–3 mm modified bitumen
3. Reinforcement layer: polyester fabric, glass fabric or combined reinforcement (provides tensile strength)
4. Bottom bitumen layer: 1–2 mm modified bitumen
5. Bottom layer: protective film or PE foil (for installation)

Total covering thickness – usually 3–5 mm per layer. Professional roofs are covered with two layers, total 8–10 mm.

Reinforcement types

• Glass fabric: economical, holds shape well but less elastic. Suitable for bottom layer;
• Polyester fabric: highly elastic, tensile resistant, ideal for top layer. Lasts longer;
• Glass + polyester combination: combines benefits. Premium class;
• Aluminium foil: not reinforcement but increases vapour resistance – suitable for dual-purpose roofs.

Installation technologies

Hot installation (torch-applied)

Traditional method. Bituminous coverings are heated with propane-butane torches (200–250°C); bitumen melts and bonds to substrate. Advantages:

• Maximum tightness
• Reliable substrate bond
• Fast work on larger areas
• Can work in various weather

Disadvantages: fire risk, requires qualified workers, unsuitable for wooden structures without additional protection.

Cold installation (gluing)

Special bituminous or polyurethane adhesives used:

• Safe – no flame
• Suitable for renovation
• Can work in enclosed spaces
• Lower noise level

Disadvantages: slower work, adhesives more temperature-sensitive, higher adhesive consumption.

Mechanical fixing

Covering fixed with special screws or nails through insulation. Used for:

• Industrial sites
• Tall buildings (wind loads)
• Quick installation
• When substrate unsuitable for hot installation

Double-layer system

Quality roof covering uses double-layer system:

1. Bottom layer – mechanically fixed or glued
2. Top layer – torch-applied to bottom

This ensures:

• Better tightness (seams don’t align)
• Increased resistance
• Longer service life (25–30+ years)
• Better covering at complex structures

Bituminous covering prices in Lithuania 2026

Material prices (m²)

• Oxidised coverings: 10–18 EUR/m²
• SBS modified: 18–28 EUR/m²
• APP modified: 20–30 EUR/m²
• Self-adhesive: 22–35 EUR/m²
• Premium SBS with polyester reinforcement: 25–35 EUR/m²

Installation prices

• Hot installation: 8–15 EUR/m²
• Cold installation: 10–18 EUR/m²
• Mechanical fixing: 7–12 EUR/m²
• Double-layer system: 15–25 EUR/m²

Total price (materials + labour)

• Single-layer system: 25–45 EUR/m²
• Double-layer system: 35–60 EUR/m²
• Premium solutions: 50–80 EUR/m²

Price typically includes: materials, installation, small details (parapets, chimneys). Separately – insulation (15–35 EUR/m²) and drainage system (8–15 EUR/m²).

Bituminous covering advantages for Lithuanian climate

Lithuanian climate – with large temperature fluctuations (-30°C winter to +35°C summer), abundant precipitation and UV. SBS bituminous coverings perfectly suit these conditions:

• Cold: SBS maintains elasticity to -40°C – no cold cracking
• Heat: APP variant resistant to +120°C, summer sun
• Moisture: all modified coverings are hydrophobic
• UV: mineral granules on top protect from sun
• Snow: strong reinforcement withstands snow loads
• Ice: elasticity withstands freeze-thaw cycles

Suitable applications and examples

New construction flat roofs

Optimal choice: double-layer SBS system (bottom glass fabric, top polyester). Ensures 30+ years service life.

Renovation projects

Recommended: self-adhesive SBS coverings or cold installation – lower risk on old buildings. Can install over existing covering after preparation.

Industrial warehouses

Optimal variant: single-layer SBS covering with mechanical fixing – fast installation in large areas, good price-quality ratio.

Multi-family residential

Classic solution: double-layer SBS system with ballast (gravel) – longevity, additional UV protection.

Green roof base

Suitable: SBS coverings with anti-root layer. Special reinforcement protects from plant root damage.

Most common installation mistakes

• Weak substrate: dirty, wet or uneven surface damages covering
• Too narrow seams: less than 100 mm – causes leaks
• Insufficient covering heat: bitumen shouldn’t be too thick or melt too much
• Layers applied too early: need 24h between layers
• In cold weather: covering below +5°C reduces tightness
• Wet substrate: causes bitumen “bubbles” after heating
• Skipped details: parapets, chimneys, vents – most common leak points

Maintenance and longevity

• Annual visual inspection (autumn)
• After storms and downpours – extra inspection
• Drainage cleaning twice a year
• Immediate small damage repair
• UV protection renewal (silver coating) every 7–10 years
• Professional audit every 5 years

Conclusions

Bituminous coverings are a practical, economical and reliable solution for Lithuanian flat roofs. SBS-modified coverings with double-layer system and polyester reinforcement ensure 25–30+ years service life. With proper material selection by building type and professional installation, bituminous covering remains the best choice for most flat roof projects.