Roof ventilation: a general overview of the main characteristics and benefits of cold roofs
Ventilated roofing is an excellent alternative to prevent condensation in winter and promote attic cooling in summer. Let’s explore what ventilated roofing is, how it works, and how to ensure optimal thermal comfort in the building with the help of a dynamic energy analysis and simulation software.
Cold Roof vs. Warm Roof
You’ve likely heard of cold and warm roofs, but what do they mean?
Every roof has distinct functional layers that determine its type. In general, roofs are grouped into four types:
- Non-insulated and non-ventilated roofing;
- Non-insulated ventilated roofing;
- Insulated and non-ventilated roofing (also known as warm roof);
- Insulated and ventilated roofing (known as cool roof).
A non-insulated and non-ventilated roof lacks thermal insulation and ventilation. This solution, due to its limited insulating capacity, is used in situations where thermal insulation is unnecessary, such as in roofs of non-residential buildings (e.g., agricultural buildings, etc.).
Non-insulated ventilated roofing is similar to the previous type but includes a ventilation layer below the sealing element. This layer aims to enhance roof performance during summer by reducing the heating effects caused by solar radiation.
A warm roof (insulated but non-ventilated roofing) has a thermal insulation layer but lacks a ventilation layer. Its composition includes a load-bearing element (such as cast-in-situ concrete slab, mixed lightweight concrete, prefabricated reinforced concrete panels, wooden panels, metal sheets, etc.), a vapor barrier, thermal insulation, waterproofing membrane, and additional works.
A cool roof (insulated and ventilated roofing) has a composition similar to a warm roof but introduces a ventilation space in the material layers, separating the layers between insulation and over-roofing.
In warm roofs, the waterproofing membrane is typically applied directly on the thermal insulation, which serves as support. In cool roofs, the waterproofing membrane is laid on the over-covering, often made of wood. Usually, warm roofs are more common, while cool roofs or ventilated roofs are preferred for wooden roofs, pitched roofs, and residential buildings.
Ventilated Roof Material Layers
Technologically, a ventilated roof must be designed with the following layers, from the inside out:
- Load-bearing structure;
- Vapor barrier layer;
- Thermal insulation element;
- Ventilation layer (created by establishing a constant-thickness gap between the roof elements and the underlying layer, achieved through double battening or the use of prefabricated panels specifically designed);
- Covering layer, with openings provided for ventilation;
- At the ridge and eaves.
In the case of a cool roof, the ventilation layer significantly improves thermal insulation, allowing the moisture produced in the building to be expelled outside the roof, preventing condensation phenomena.
The natural gap, which separates the covering layer from the underlying insulation layer, facilitates “ascending convective movements.” These convective movements extract much of the heat that would otherwise be transmitted to the underlying layers, allowing moisture to escape without compromising the thermal insulation power of the underlying layers and the gap itself.
To activate this mechanism, external air must enter the gap at the eaves level and exit from the ridge through a venting element. This process helps keep the insulating material dry during winter, avoiding condensation, while in summer, the fresh air entering from the eaves warms up in the gap and exits from the ridge, extracting heat from the structure.
Summer insulation of the roof is important, especially with rising temperatures. A ventilation layer adds value to insulating materials, which usually have good performance in retaining heat inside the building but may struggle to protect against heat or resist high temperatures in the under-roof space.
Moreover, a ventilated roof ensures longer durability of the covering layer elements, which can dry quickly both inside and outside, reducing the risk of breakage in case of freezing. Ventilated roofs can help reduce temperature after hours of intense sunlight exposure in summer, improving the thermal comfort of the under-roof space.
If the air gap does not meet specific parameters outlined by regulations, it is referred to as micro-ventilated roofs, characterized by a more contained air chamber and a faster and simpler installation. Micro-ventilation under-roof is used to prevent moisture accumulation, condensation formation, and extend the lifespan of the roofing system. In micro-ventilated roofs, especially for pitched roofs on cast-in-situ concrete slabs, the sheets have special grooves in the under-roof covering to facilitate upward movement of the air current from the eaves to the ridge, enhancing thermal and hygrometric performance of the structure.
Evaluating Project Energy Performance
To assess the energy efficiency of your project, it’s advisable to use a dynamic energy analysis and simulation software. This allows you to model the entire building in 3D, assign materials and characteristics to all layers (roofing, vertical enclosures, windows, etc.), set general parameters and climatic data for the location, define the hourly schedule for dynamic energy simulation, automatically identify and resolve thermal bridges, simulate the energy behavior of the building, and perform dynamic energy simulations with the model under real operating conditions.
This way, you can understand the actual energy consumption of the building, the main factors influencing such consumption, and the energy performance of different materials and design solutions.
Below is a brief video illustrating how to manage vertical and horizontal stratifications (roofing and floors) of your project building, an essential step before starting the dynamic energy calculation of the building.
Benefits of Ventilated Roofing
Ventilated roofing offers several benefits, especially when designed and installed correctly. Here’s a summary of the main advantages of a ventilated roof:
Moisture Control: Ventilation allows air circulation under the roof, reducing the risk of moisture buildup. This is crucial to prevent mold formation and moisture-related damage.
Thermal Regulation: Ventilation helps maintain a more uniform temperature in the space under the roof. This is useful both in winter and summer, reducing excessive heat accumulated under the roof.
Increased Energy Efficiency: Proper ventilation can enhance the energy efficiency of the building. By reducing heat buildup in summer, the need for artificial cooling can be minimized. In winter, ventilation can help keep the insulation material dry, maintaining its thermal efficiency.
Extended Lifespan: Good ventilation can contribute to preserving the roof structure and materials used (insulation, tiles, battens, etc.), thus ensuring a longer lifespan. By reducing moisture and extreme temperature changes, premature damage can be avoided.
Enhanced Living Comfort: Proper ventilation contributes to creating a more comfortable indoor environment. This is particularly important if the attic space is used for living or working.
Reduced Condensation Risk: Ventilation reduces the risk of condensation formation inside the roof, especially in cold climates. This is crucial to prevent damage to insulation materials and the underlying structure.
Improved Indoor Air Quality: Adequate ventilation helps maintain the air quality under the roof, removing moisture and preventing the formation of unpleasant odors or mold.
Adaptability to Different Climatic Conditions: Ventilated roofs are suitable for various climates, as they can be designed to adapt to specific heating or cooling needs based on the geographic region.
Sustainability: Energy efficiency and extended durability can contribute to sustainability efforts, reducing the environmental impact of buildings over time.