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Roof insulation is one of the key tasks in the construction and renovation of both residential and industrial buildings. The question of choosing and properly installing insulation under the screed — a structural element that provides not only thermal insulation but also a base for the subsequent roofing layer — is especially relevant.
Screed is used to create a level surface, distribute loads, and protect insulation from mechanical damage. The correct selection and installation of thermal insulation under the screed directly affect indoor comfort, energy savings, and the durability of the entire roofing system.
In this article, all aspects related to insulation for roofing under screed will be extensively discussed — types of materials used, installation features, regulatory requirements, influence of operating conditions, and recommendations for optimal solutions.
The Importance of Insulation Under Screed
Insulation in the roofing system plays a vital role in thermal protection. It prevents significant heat loss through the roof, helping maintain a stable indoor temperature regardless of external conditions.
Under the screed, insulation receives additional protection against mechanical loads, UV radiation, and moisture, significantly extending its service life. Moreover, insulation under screed helps solve soundproofing tasks and ensures the overall energy efficiency of the building.
Without proper insulation and quality installation under the screed, thermal bridges, condensation, and even mold growth may occur, negatively affecting inhabitants’ health and increasing operational costs.
Main Types of Insulation for Roofing Under Screed
Specialized thermal insulation materials with necessary strength and load resistance are used under screed.
Expanded polystyrene (EPS) is one of the most common insulations. It features high strength with relatively low weight, moisture resistance, and long service life. Extruded polystyrene foam (XPS) is used in cases of increased load and humidity due to higher density and lower water absorption.
Mineral wool holds a firm position among traditional insulations. However, it is used less often under screed, as deformation and moisture penetration decrease its insulating properties and cause destruction. Mineral wool requires additional waterproofing and vapor barriers.
Polyurethane boards and spray foam combine excellent thermal properties with strong adhesion but have higher costs and require professional installation.
Key Requirements for Insulation Under Screed
Insulation under screed must meet several technical criteria. Primarily, it must have high load-bearing capacity to withstand static and dynamic loads from the screed mass, equipment, operation, and possible mechanical impacts.
Water resistance or minimal water absorption is essential, especially in roofing exposed to moisture risks. The material must retain its insulating properties in contact with moisture and resist degradation over time.
Additional requirements include resistance to temperature fluctuations and deformation, fire safety, and durability. The insulation should not emit toxic substances and must resist biological activity such as mold and microorganisms.
Roofing System Design Features with Insulation Under Screed
Structurally, roofing with insulation under screed can be executed in various ways. The most typical example is the roofing “pie,” consisting of a supporting base, insulation layer, reinforced screed, waterproofing, and final roofing material.
In accessible roofs, insulation is often laid on top of waterproofing, after which comes the screed, creating a level surface for paving slabs, lawns, or other coverings. In non-accessible roofs, the screed primarily distributes load and protects insulation.
Insulation thickness is selected depending on climatic conditions, building purpose, and insulation standards. Multilayer systems have rules for alternating materials to protect insulation and ensure indoor comfort.
Insulation Installation Technology Under Screed
Insulation installation under screed starts with substrate preparation—cleaning from dust, dirt, and unevenness. Leveling may be required depending on the base condition.
Insulation panels are laid tightly without gaps, with secure fitting between elements. For hygroscopic materials, vapor barriers are recommended.
The installed insulation is mechanically fixed or pressed by a reinforced screed. Reinforcement with metal or polymer mesh improves strength and prevents cracking.
The next step is waterproofing to protect insulation and screed layers from moisture. Sometimes waterproofing exists beneath the insulation, requiring vapor barriers over the screed.
Properties of Popular Insulation Types for Roofing Under Screed
Extruded Polystyrene Foam (XPS)
Has a high density of 25 to 40 kg/m³, providing compressive strength from 300 to 600 kPa. Water absorption is minimal—less than 0.5% due to closed-cell structure. Resistant to rot and microorganisms, with low thermal conductivity of about 0.030–0.034 W/(m·K).
Installation is simple and fast, reducing labor costs. Proper installation may lead to a service life exceeding 50 years.
Common Polystyrene Foam (EPS)
Lower density — around 15–25 kg/m³, thermal conductivity approximately 0.038–0.041 W/(m·K). Higher water absorption makes it less moisture-resistant. Used mainly in low-humidity or protected spaces.
Its affordability makes EPS popular when budgets are limited.
Mineral Wool
Known for good vapor permeability, benefiting ventilation within the roofing system. Density and strength vary by grade, typically 30–150 kg/m³. Loses insulation value when wet. Requires reliable waterproofing and vapor barriers.
Influence of Insulation Types on Roofing Operation
Choosing insulation under screed directly affects the roof’s longevity and energy efficiency. Materials with low water absorption and high strength, like XPS, enable reliable systems with minimal repair and maintenance costs.
Insulation with high vapor permeability helps remove condensation from the structure, especially in humid climates with significant daily temperature swings.
Moisture-vulnerable materials or ones unable to withstand loads deteriorate quickly, causing screed defects, roof damage, and thermal protection loss.
Importance of Correct Insulation Thickness Under Screed
Insulation thickness determines thermal resistance. Insulation standards depend on climate zone, building function, and energy efficiency requirements.
Optimal thickness balances heat loss reduction and economic feasibility. Too thin layers fail to insulate properly, increasing heating or cooling costs.
Excessive thickness increases structural loads, screed volumes, and material and labor expenses. A balanced choice ensures efficiency and economy.
Influence of Screed Design on Insulation Selection
Screeds may be reinforced or plain, thin or thick layers, affecting the load applied to insulation. Materials with different densities behave differently under load.
With rigid, reinforced screeds, less strong insulation may be used but must provide smoothness and avoid point load stresses.
For trafficked roofs with pavers or greenery, insulation requires exceptional load resistance to prevent deformation and loss of thermal performance.
Repair and Maintenance of Roofs with Insulation Under Screed
Regular roof inspection helps detect early-stage problems: screed cracks, moisture accumulation, deformation. Damaged insulation beneath screed can degrade thermal performance.
Repairs involve careful partial removal of screed to replace damaged insulation. Quality materials and professional installation reduce repair frequency.
Proper maintenance and timely fixes extend roof life and maintain indoor comfort.
Comparative Characteristics Table of Popular Insulations for Roofing Under Screed
| Characteristic | Extruded Polystyrene Foam (XPS) | Polystyrene Foam (EPS) | Mineral Wool |
|---|---|---|---|
| Density, kg/m³ | 25–40 | 15–25 | 30–150 |
| Thermal Conductivity, W/(m·K) | 0.030–0.034 | 0.038–0.041 | 0.035–0.045 |
| Water Absorption, % | <0.5 | 2–5 | up to 20 |
| Compressive Strength, kPa | 300–600 | 100–200 | 50–200 |
| Vapor Permeability | Low | Medium | High |
| Mold Resistance | High | Medium | Low |
| Service Life, years | >50 | ~25 | ~20–30 |
Conclusion
Insulation for roofing under screed is a vital component ensuring effective thermal protection and long service life. Correct material choice and installation technology influence roof quality, building energy efficiency, and indoor comfort.
Primary criteria for insulation selection are strength, water resistance, thermal conductivity, and durability. Extruded polystyrene foam leads today thanks to its combined performance and ease of installation.
Experts recommend careful thickness calculation, adherence to installation technologies, and correct waterproofing and vapor barrier systems for optimal results and longevity.