A suitable value of the air-light ratio is essential to certify the correct lighting of a building structure. The construction and renovation of buildings must in fact strictly comply with the building regulations to acquire all the necessary requirements.
For any building, an opening to the outside must be ensured, so as to have natural lighting and ventilation for the walkable surfaces of the buildings. In this sense, the air-light ratio plays an important role in ensuring a correct level of air-lighting of a house over time.
But what is it, how is it calculated and what legislation governs this value?
In the following paragraphs we go into detail to learn more about this delicate topic and to understand its importance for the usability and use of buildings.
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What is the air-light ratio?
In concrete terms, when we talk about the air-illuminating ratio, we are referring to the ratio that connects the extensions of the windowed and glazed surfaces through which sunlight passes and the total paved surfaces. In even simpler words, the RAI is useful for evaluating how much natural light and ventilation filters into an environment, a necessary requirement for the habitability and use of a property.
A building, an office or even a room can be correctly defined as aeroilluminating if the ratio between the 2 values is equal to or greater than 1 to 8. Otherwise, the environment in question does not comply with the relevant regulations.
In turn, the RAI ratio is divided into two values:
- enlightening report (RI): referring to the useful illuminating surface through which sunlight passes;
- aerating ratio (RA): refers to the relationship between the air circulating in a building and the useful ventilation surface of the openings.
In a home or in any other environment, ensuring a correct level of air-light ratio is not only required by law but also brings several important benefits, including:
- suitable air recirculation in the building for a liveable and healthy environment;
- reduction of energy costs, greater environmental protection and limited use of artificial light;
- property prevention against mold and humidity.
Today, the calculation of the aero-illuminating ratio is one of the various initiatives to promote a virtuous use of energy sources. A perfect knowledge of the concept of aero-illuminating ratio is essential to understand the real importance of its value, for the purposes of a building characterized by healthy environments and respectful of regulatory dictates.
The legal obligation and the advantages deriving from a correct value cannot be ignored when building or renovating a property, it would be a serious shortcoming from every point of view. It is not only a fulfillment to be carried out for the purposes of a legal obligation, but also a necessary practice for the protection of the environment in which one lives or works.
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How is it calculated?
Once you understand the concept and importance of such a practice, the following question is legitimate: how do you calculate the air/light ratio?
To calculate this value, a mathematical equation is needed, which must generate a result in line with the usability standards required by law. In this regard, the RAI must be calculated separately for each room that makes up the building.
To obtain the relative ratio, simply divide the total of the surfaces with windows by the walkable and paved ones. For an acceptable air-lighting ratio, the result of the division must be greater than the value 0.125 (ratio 1 to 8). This latter is a parameter established by law, otherwise it would in fact mean that the air-lighting ratio of a room does not comply with the regulatory provisions and the environment in question would not be habitable.
Municipal and regional regulations in the case of offices, shops and commercial premises, can also lower or raise this ratio. For this reason, before calculating the RAI, it is necessary to be well informed about the specifications of municipal and regional regulations. A necessary precaution to avoid incurring some harmful calculation errors.
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The reference legislation
The reference legal provision for the air-lighting ratio is Article 5 of the Ministerial Decree of 5 July 1975. This regulation states that the size of the windows of a building must ensure daylight illumination greater than 2% and an air-lighting ratio greater than 0.125. This value, in addition to certifying correct natural lighting and ventilation of a building, must be greater than 0.125 for the certification of the habitability of a building.
The regulations for private homes establish the obligation of direct natural lighting for each room of the home, with the exception of corridors, hallways and toilets. For companies, schools, offices and public places, the air-lighting ratio is always set at a minimum ratio of 1 to 8.
The calculation of the RAI cannot therefore ignore the expected regulatory provisions and compliance with the minimum values established by law. These are mandatory regulatory provisions in the case of new building constructions, renovations and changes in the intended use of rooms and spaces and in the case of internal modifications, except for any derogations.
For example, when transforming a balcony into a veranda, the result of the air-light ratio is binding for a building intervention in compliance with the law. In the case of such a building intervention, it is therefore essential to rely on a professional (architect, engineer or surveyor) with the right skills to deal with the formalities of the case, starting from the Regulatory Plan and the related Building Regulations to check the real feasibility of an increase in volume.
Among the various checks, the professional in charge will also have to calculate the air-lighting ratio, a practice to understand if the value is sufficient to satisfy the required municipal regulations.
However, there are some special cases, that is, exceptions to the strict observance of the minimum limit of the air-lighting ratio. These exceptions refer to historic buildings, for which it is impossible to make changes to regularize the RAI ratio. We are talking about those buildings considered historic and built before 1975, not affected by the change of intended use.
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The usefulness of the air-light ratio
From what has been said so far, it is easy to understand how a very low air-lighting ratio does not allow for proper air recycling, compromising the healthiness of the environments involved. Poorly ventilated or closed environments often cause the formation of water vapor and carbon dioxide, causing shortness of breath, headaches or weakness among the inhabitants of the building. Inadequate windows do not allow for proper lighting of the environments, with the consequence of resorting to artificial light and increasing waste and energy costs in the bill.
Therefore, the purpose of the air-lighting ratio, regulated by Article 5 of the Ministerial Decree of 5 July 1975, is to ensure that buildings have suitable requirements regarding healthiness, safety, hygiene and energy saving.
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FLDm (Average Daylight Factor)
The building regulations also refer to the Average daylight factoranother important indicator that characterizes internal lighting. This is a useful parameter for evaluating the natural daytime lighting of windowed or closed spaces regardless of the hours, days and climatic seasons of the year, but considering possible objective obstructions of a permanent nature.
The Average Daylight Factor is calculated by weighting the average of the FDL (Point Daylight Factor) on the internal surfaces of the entire room. In turn, the Point Daylight Factor is determined by the ratio between the illumination measured at a specific point in the interior spaces and that measured outside.
The reference regulation provides for a minimum threshold set at 2%, but logically a higher Average Daylight Factor ensures better visual conditions and savings on energy bills. The calculation of the FLDm (Average Daylight Factor) is more complex than that of the RAI, since it requires more sophisticated calculations and specific software.
Instead, the air-light ratio system is tabular and easier to use.
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Conclusions
In the building sector, RAI is an essential factor for providing environments with hygiene, safety and healthiness and for reducing energy bill costs. When building or renovating a house or any type of property, calculating the air-lighting ratio is crucial for healthy environments, not only to comply with a legal obligation.
The RAI is regulated by the aforementioned article 5 of the Ministerial Decree of 5 July 1975, but before any calculation action it is also a good idea to know any clarifications and derogations of the municipal and regional regulations.
Having adequate natural lighting and air recycling at home is essential for the well-being of those who spend entire hours of the day in the family environment. Spending entire days in livable and healthy places is very important for our health and for safeguarding the environment. The impact on costs should not be underestimated either because reducing the use of artificial lighting allows for significant energy savings.
Finally, a property that is not properly lit and ventilated is exposed to problems of mold and humidity, with the risk of a fairly early deterioration of the structures.
