A complete guide to thermal bridges in pitched roofs and flat roofs. What causes it, usual problems, insulation strategies and benefits resulting from proper design.
Designing thermal bridges is crucial in the construction field and requires special attention as it determines the habitability, energy efficiency and occupants’ health. In the specific context of the roof, thermal bridges can lead to heat loss, mold formation and condensation. Significantly impacting the building structure and occupants’ well-being.
This article aims to explore in-depth all aspects related to thermal bridges in pitched roofs and flat roofs. A video will also show you how to easily address the issue with specific thermal bridge calculation software equipped with an integrated FEM solver, wizards for standard cases, and DXF/DWG scheme import.
Causes of Thermal Bridges in Roofs
Fully understanding the underlying causes of thermal bridges in roofs is essential to effectively address the issue. A thermal bridge, defined as a localized area of the building envelope with lower thermal resistance than the remaining portion without thermal bridges, represents the focal point of thermal flow between a building’s internal and external environment.
Various inconsistencies contributing to thermal bridge formation include:
- Geometric inconsistencies in the building envelope
Wall-floor nodes, wall-column nodes and wall-window nodes are critical points where geometric inconsistencies can occur. These areas, if not treated correctly, can become true “breaches” in the building’s thermal barrier;
- Building envelope thickness variations
Elements like recesses, technical voids and chimneys can cause variations in the envelope’s thickness. These discontinuities can disrupt thermal insulation coherence, facilitating heat dispersion through these areas;
- Material inconsistencies
The presence of different materials or the transition from one material to another can contribute to thermal bridge formation. Material inconsistencies can alter the building envelope’s thermal insulating capacity, creating vulnerable points;
- Specific building phenomena
Other building-specific factors, such as the presence of structural bridges or suboptimal design solutions can also contribute to thermal bridges.
Issues Arising from Thermal Bridges in Roofs
We have already mentioned that thermal bridges in the roof can cause significant problems both in terms of living comfort and building’s energy efficiency. Let’s delve into more detail.
Impact on Thermal Loss
Thermal loss resulting from roof’s thermal bridges is responsible for considerable energy losses. This phenomenon compromises the overall building’s thermal insulation efficiency. Affecting occupants’ thermal comfort and increasing energy consumption.
Mold and Condensation
The formation of mold and condensation is a tangible risk associated with thermal bridges in the roof. This phenomenon occurs when areas affected by thermal bridges become colder than the rest of the building, creating an environment conducive to condensing the moisture in the air. This condition, besides compromising the structural integrity of the roof, it poses a threat to occupants’ health.
Thermal bridges in the roof can indeed compromise indoor air quality, increasing the risk of respiratory diseases and allergies.
Thermal Bridges Attacking with the Roof Covering
In intermediate floors and connection zones with the roof covering, structural continuity between the horizontal or inclined plane and the vertical one can generate thermal bridges, especially when considering flat roofs. The connection between the wall and the roof covering can be influenced by the roof covering structure itself, with elements such as copings, eaves lines or vertical parapets that can interrupt geometric continuity.
If the wall extends beyond the roof slab, with a parapet or other vertical element, it can interrupt the continuity of the insulation layer. In this case, it is essential to carefully manage the connection between the parapet and the insulation layer, paying attention to dimensions and materials involved.
In the context of a pitched roof, thermal bridge formation requires careful consideration of the different geometry resulting from the connection between the roof’s inclined part and the vertical wall. This aspect is particularly relevant when considering connecting elements such as beams, especially in cases of wooden floors.
Alternatively, the roof covering could adopt a “ventilated roof” configuration, with the upper part facing outward and separated from the lower part by an air layer. Although this configuration promotes proper ventilation, it may introduce critical points in terms of thermal insulation.
Elements such as copings, shelves, or architectural solutions in connections between inclined roofs and walls may protrude beyond the roof covering profile, generating potential interruptions in the insulation layer continuity and becoming sources of thermal dispersion if not designed and executed with care. Therefore, it is crucial to adopt design approaches to ensure insulation layer continuity. Minimizing thermal bridges’ impact and ensuring optimal thermal performance in the entire pitched roof system.
Benefits of Roof Insulation
Roof insulation represents an effective solution to improve the energy performance of a building. A widely adopted technique is internal roof insulation, involving the application of specific materials to block heat passage in both seasons. One of the most common techniques is the use of insulating panels, although it’s important to note that this practice can be aesthetically invasive.
Blown Insulation as a Non-Invasive Technique
Blown insulation is emerging as a convenient and ecological alternative. This practice, devoid of invasive external and internal interventions, preserves the building’s aesthetic aspect. Insulating materials like cellulose fiber and glass wool are often used in this methodology, ensuring reduced environmental impact and containment of thermal losses through the roof.
The possibility of blowing insulation directly from above, maintaining the existing roof, offers a practical advantage with reduced time and costs compared to traditional solutions. This approach is particularly convenient when there is access to a free cavity, as in the case of roof covering maintenance.
Materials for Eliminating Roof Thermal Bridges
Commonly used insulating materials to eliminate thermal bridges include:
- cellulose fiber: biodegradable and ecological, offers heat resistance and waste reduction;
- glass wool: widely used for its excellent insulating properties, fire resistance and ease of installation;
- polyurethane foam: closed-cell insulation that adheres without joints, effective in filling voids;
- expanded polystyrene (EPS): lightweight, durable, moldable, suitable for various roof shapes and waterproof.
Common Mistakes in Roof Insulation
It is important to be aware of common mistakes that can compromise work effectiveness:
- Use of inappropriate materials
The choice of insulating materials is crucial. Opting for cheap or low-quality solutions can reduce the effectiveness of thermal insulation. Consult industry professionals to make the most suitable and functional choice for specific needs;
- Ignoring ventilation
Proper ventilation is essential to prevent condensation and mold formation. Ensure you have an adequate system that allows proper air circulation under the roof, crucial for the final result contributing to maintain a healthy environment;
- Not paying attention to leaks and cracks
Even the smallest cracks in the roof can compromise the effectiveness of thermal insulation. Conduct a thorough roof inspection, looking for any weak points. Repair them before proceeding with any installation is an essential point for the work’s success;
- Ignoring the importance of proper installation
Even with quality materials, improper insulation installation can reduce its effectiveness. Relying on industry professionals for correct implementation is essential.
By carefully following these guidelines and paying attention to avoidable mistakes, it is possible to achieve optimal roof insulation from the inside. Ensuring a comfortable home environment, reducing energy costs and preventing issues related to moisture and mold formation.
How to Design and Calculate Roof Thermal Bridges Considering Real Conditions
In the following video, you can see how thermal bridge calculation software allows you to design structures identical to real conditions obtaining highly professional results thanks to a finite element analysis solver.