Compact flat roofs (also called sutapdinti stogai in Lithuanian) are a very popular roof type in Lithuania for both residential and commercial buildings. The term refers to a roof construction where thermal insulation, waterproofing and load-bearing structure are tightly joined in one system – without ventilation gap.
This article describes compact flat roof construction, layers, installation stages, prices for 2026 and specific requirements for Lithuanian climate conditions.
What is a compact flat roof?
A compact flat roof is a construction where:
- Roof covering layer is directly on thermal insulation
- Thermal insulation – on vapour barrier and load-bearing structure
- NO ventilation gap between insulation and covering
- The whole system works as one continuous layer
This differs from “dual roof” (ventilated) system, which has a separated ventilation gap between covering and insulation.
Compact flat roof layer structure
The most popular 7-layer system in Lithuania (bottom to top):
- Load-bearing structure – reinforced concrete slab, profiled metal or wooden elements
- Vapour barrier – PE film or bituminous membrane preventing vapour from reaching insulation
- Thermal insulation – mineral wool, EPS, XPS or PIR boards (thickness 20–35 cm)
- Slope-forming layer – insulation boards with 1–3% slope
- Bottom waterproofing layer – SBS bituminous covering (4 mm)
- Top waterproofing layer – SBS bituminous covering with mineral granules (4–5 mm)
- Protective layer (if trafficable) – gravel, concrete pavers or terrace covering
Total thickness: 25–45 cm depending on energy class.
Compact flat roof advantages
- Space saving – no ventilation gap (more compact construction)
- Good energy efficiency – proper thermal insulation
- Lower cost – simpler construction than ventilated roofs
- Modern design – fits contemporary architecture
- Functionality – can install terraces, gardens, solar plants
- Faster installation – simpler technology
Compact flat roof drawbacks and risks
- Moisture risk – if vapour barrier improperly installed, moisture accumulates in insulation
- More complex repair – damage opens whole system
- Requires precise design – U-value, vapour migration must be calculated
- Special installation requirements – only experienced craftsmen
Compact flat roof types
1. Traditional compact (cold roof)
Classic system with vapour barrier inside. Suits standard projects.
2. Inverted compact (warm roof)
Thermal insulation (XPS) is ABOVE waterproofing. Advantages:
- Waterproofing protected from UV and mechanical impact
- Serves up to 50 years
- Suits trafficable roofs
- Requires XPS insulation (moisture-resistant)
3. Combined compact (duo-roof)
Hybrid solution – insulation BEFORE and ABOVE waterproofing. Highest energy class.
4. Green compact
With vegetation layer above covering. Special requirements for anti-root protective layer.
Planning a roofing project?
Get in touch for a free consultation and a tailored quote for your building.
Compact flat roof installation stages
1. Design (1–2 weeks)
- Thermodynamic calculation (U-value, vapour migration)
- Structural load analysis
- Drainage scheme creation
- Material specification
2. Substrate preparation (1–2 days)
- Construction cleaning and priming
- Smoothness ensuring (max 5 mm/m)
- Moisture removal
3. Vapour barrier installation (1 day)
- PE or bituminous film
- All joints sealed tightly
- Min. 100 mm overlap
4. Insulation installation (2–4 days)
- Boards glued or mechanically fixed
- Layers compacted without gaps
- Slope formation with slope boards
5. Waterproofing installation (3–5 days)
- Bottom layer torching
- Top layer torching (seams don’t align)
- Detail finishing (parapets, chimneys)
6. Drainage and finishing (1–2 days)
- Drainage channel formation
- Downpipe fixing
- Final tightness test
Compact flat roof prices 2026 (Lithuania)
| System type | Price EUR/m² |
|---|---|
| Economy (simple SBS, EPS 20 cm insulation) | 50–75 |
| Standard (SBS double, mineral wool 25 cm) | 75–110 |
| A++ class (premium SBS, PIR 22 cm) | 110–160 |
| Trafficable (with gravel or pavers) | 140–220 |
| Inverted (XPS above covering) | 120–180 |
| Green | 180–280 |
Sample budget – 150 m² A++ class compact flat roof
- Vapour barrier: 4 × 150 = 600 EUR
- PIR boards 22 cm: 38 × 150 = 5,700 EUR
- Slope boards: 1,200 EUR
- SBS double-layer system: 50 × 150 = 7,500 EUR
- Drainage: 13 × 150 = 1,950 EUR
- Parapets (50 m): 30 × 50 = 1,500 EUR
- Lightning protection: 1,800 EUR
- Design: 800 EUR
- TOTAL: ~21,050 EUR (140 EUR/m²)
Planning a roofing project?
Get in touch for a free consultation and a tailored quote for your building.
Lithuanian climate requirements
U-value (2026 regulations)
- B class: U ≤ 0.18 W/m²K (≈22 cm wool)
- A class: U ≤ 0.16 W/m²K (≈25 cm wool)
- A+ class: U ≤ 0.15 W/m²K (≈28 cm wool)
- A++ class: U ≤ 0.12 W/m²K (≈32 cm wool or 22 cm PIR)
Vapour migration control
Winter conditions (-25°C outside, +20°C inside) require:
- High Sd value vapour barrier inside
- Diffusive layer above insulation
- Precise calculation per LST EN ISO 13788
Snow load
Lithuania: 110–180 kg/m² depending on region. Vilnius area – up to 150 kg/m².
Most common mistakes
- Without design – U-value and vapour migration not calculated
- Vapour barrier damage – small gap will cause whole system wetting in 1–2 years
- Non-compacted insulation layers – gaps cause cold bridges and condensation
- Insufficient slope – <1% causes standing water pools
- Wet insulation – installing in rain loses 30–50% efficiency
Conclusions
Compact flat roof is a reliable, energy-efficient solution for flat roofs. In Lithuania, both traditional (with internal vapour barrier) and inverted (XPS above covering) types are popular. Investment 50–150 EUR/m² – depending on energy class and layers. Most important – precise design, qualified installation and regular maintenance. Properly installed compact flat roof serves 25–50+ years.
Frequently asked questions
A compact flat roof is a flat roof construction where thermal insulation, waterproofing and load-bearing structure are joined in one system WITHOUT ventilation gap.
Compact has no air gap between insulation and covering – all layers compacted. Ventilated has separated air gap that ventilates insulation.
Economy solution – 50–75 EUR/m², standard – 75–110 EUR/m², A++ class – 110–160 EUR/m². Trafficable or inverted – 120–220 EUR/m².
A++ class requires U ≤ 0.12 W/m²K – corresponds to 32 cm mineral wool, 28 cm XPS or 22 cm PIR boards.
Traditional – cheaper, most popular. Inverted (XPS above covering) – serves up to 50 years, waterproofing protected. Inverted 15–25% more expensive but durability pays back.
Yes, with trafficable compact construction with reinforced base, mechanically resistant coverings and ballast (gravel or pavers). About 30% more expensive than standard.
Through proper vapour barrier (Sd value 100+ m), precise design per LST EN ISO 13788 and qualified installation without gaps. Moisture problems often arise from poor vapour barrier.
Traditional compact serves 25–35 years, inverted – up to 50 years. Depends on covering quality, design and maintenance. Regular inspection (2× per year) extends service.
Yes, with proper insulation (32 cm wool or 22 cm PIR) and quality waterproofing. PIR boards allow smaller construction thickness – fits height-restricted projects.
Compact flat roof installation requires experienced design and precise installation. Choose contractor with 5+ years experience in compact roofs, design capabilities and quality materials.
