Thermal insulation represents one of the most effective interventions for improving the energy performance of an existing home. In Italy, a large portion of the residential building stock was constructed before the introduction of the first energy consumption regulations, which came into force progressively between the 1970s and 1990s. This means that millions of buildings still have walls without insulation, poorly insulated roofs, uncorrected thermal bridges, and windows with outdated performance.
The consequences are well known to those living in these homes: cold walls during winter, rooms that overheat quickly in summer, mold in the most exposed corners, high energy consumption, and a feeling of discomfort that often persists even when the heating system is running: if you are considering renovating your home, thermally insulating the property and improving its energy efficiency is certainly an intervention worth evaluating.
Each insulation intervention, however, has specific characteristics, different costs, and application contexts that must be evaluated on a case-by-case basis: let’s examine them one by one.
External Insulation System
The external thermal insulation system represents the benchmark against which all other solutions are compared: it consists of applying insulation panels to the external surface of perimeter walls, subsequently covered with reinforced rendering and protected by a final finish layer resistant to weather conditions.
From a technical standpoint, the main advantage of external thermal insulation lies in the fact that the entire masonry remains within the conditioned volume. This aspect produces very important effects on the building’s thermal behavior.
During winter, the heat produced by the systems is stored by the masonry structures and gradually released, helping to maintain stable indoor temperatures even when the heating is turned off. During summer, the masonry slows the transmission of heat from outside, improving comfort in interior spaces.
Energy savings simulations performed on Italian residential buildings show that a properly designed thermal insulation system can reduce heating energy requirements by 20% to over 45%, with particularly high values in buildings constructed before the 1980s.
Naturally, the result depends on numerous factors: insulation thickness, climate zone, building orientation, and installation quality. The main disadvantage of thermal insulation systems is the initial investment: the cost of an external insulation system averages between €70 and €150 per square meter, but in complex buildings or those with articulated facades, higher values can be reached.
Internal Thermal Insulation
It is not always possible to intervene on a building’s facade: in condominiums it is complicated to agree on such an intervention, but also in historic centers or buildings subject to architectural protection, external insulation is not a viable solution.
In these cases, internal thermal insulation often constitutes the only possibility for improving the insulation of perimeter walls: it consists of creating an insulated counter-wall on the internal side of the masonry. The thickness generally varies between 5 and 12 centimeters, depending on the required performance and available space.
The improvement is often immediate: internal surfaces are warmer and the sensation of radiant cold that characterizes poorly insulated buildings decreases significantly: however, compared to external insulation, the existing masonry remains exposed to external climatic conditions and loses much of its heat storage capacity, resulting in less stability of internal temperatures over the long term.
Moisture and condensation phenomena can also occur within the wall, which is why the design of internal insulation always requires accurate hygrothermal verification.
The energy savings achievable with internal thermal insulation generally range between 15% and 35%, with results that strongly depend on the continuity of the intervention and the presence of residual thermal bridges.
Cavity Wall Insulation
Many buildings constructed between the 1960s and 1990s have walls consisting of two masonry layers separated by an air cavity, as it was believed that the cavity was sufficient to ensure good thermal insulation.
Cavity wall insulation consists of filling this cavity with loose insulating materials such as cellulose, mineral wool, or expanded polystyrene beads, capable of uniformly occupying the available spaces and significantly reducing heat transmission.
It is a minimally invasive intervention: in most cases the work is completed in one or two working days without requiring scaffolding, demolition, or significant masonry work.
From an energy standpoint, the results can be remarkable. Heat loss through perimeter walls can decrease by 40% to 70%, generating a reduction in overall consumption often between 10% and 25%.
Cavity wall insulation has costs generally between €15 and €35 per square meter, and often represents the first intervention to evaluate in buildings with cavities.
Roof Insulation
When analyzing a building’s heat loss, the roof frequently emerges as the most critical element: warm air naturally tends to rise upward, so in a poorly insulated home, a significant portion of the energy used tends to be lost through the roof.
Roof thermal insulation can be installed from either the outside or inside; the former, generally performed during roof replacement, allows the best results thanks to the continuity of the insulation layer and the reduction of thermal bridges.
Particularly interesting is the ventilated roof solution, in which an air layer is created between the insulation and the roof covering that in summer facilitates the dissipation of heat accumulated by the roof, reducing overheating of the spaces below.
Eliminating Thermal Bridges
When discussing thermal insulation, attention tends to focus on the largest surfaces, such as walls and roofs, but many problems derive from relatively small areas characterized by high energy loss, such as concrete balconies that penetrate the facade, pillars embedded in walls, shutter boxes, and connections between walls and roofs: these zones are called thermal bridges.
At thermal bridges, the temperature difference compared to surrounding areas can generate condensation: many problems apparently related to moisture are actually direct consequences of the presence of thermal bridges.
Eliminating thermal bridges requires specific interventions that vary depending on the construction situation. In some cases, integrating the thermal insulation system is sufficient; in others, dedicated systems or more complex structural modifications are necessary.
From an energy efficiency standpoint, the contribution of thermal bridges may appear limited compared to main surfaces. However, their impact on living comfort and environmental healthiness is often decisive.
Window Replacement
Windows represent one of the most delicate elements of the building envelope: they must simultaneously ensure natural lighting, ventilation, visibility, and protection from weather conditions.
For decades, Italian buildings were equipped with single-glazed windows or first-generation double glazing characterized by energy performance now far below current standards.
Modern windows employ low-emissivity glass, chambers filled with insulating gases, and multi-chamber frames designed to limit heat loss.
The improvement in comfort is immediately noticeable. Glass surfaces are warmer during winter, condensation formation is reduced, and most of the drafts that characterize older windows disappear.
Energy benefits depend on initial conditions. Replacing very outdated windows can result in consumption reductions between 10% and 20%, with even better results when the intervention is accompanied by correction of thermal bridges in the window opening.
Costs are extremely variable depending on material, dimensions, and required insulation performance.
The best results for home thermal insulation are obtained when interventions are designed as parts of an overall strategy: in a typical Italian home built between the 1960s and 1990s, the combination of wall insulation, roof insulation, thermal bridge correction, and window replacement can reduce heating energy requirements by over 50%, simultaneously improving comfort, environmental healthiness, and the property’s economic value.
Many thermal insulation and energy efficiency interventions for properties are eligible for tax deductions up to 50% through the 2026 ecobonus.
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