A good roof insulation from cold but also from heat it is important to save energy and for living comfort. In fact, it is not uncommon for heat losses through the roof to make up 30-40% of the overall losses of a building in winter. And it's not uncommon for the bad either roof insulation cause overheating of the attics and an increase in air conditioning costs in the summer.
The percentage is higher in small-sized buildings, where the influence of the roof element on living well-being in the hot season is even more pronounced. The roof is in fact subjected more than the walls to solar radiation and in the absence of a good one roof insulation the rooms below, typically the attics and attics, overheat until they become unlivable and, in turn, transmit heat to the rooms below.
A good roof insulation it helps to reduce the power of technological systems and with it the costs associated with both winter heating and summer air conditioning. The evaluation criterion of a roof insulation however it changes depending on whether we are talking about protection from cold or heat.
In the winter for a good roof insulation the thermal conductivity of the insulating material counts. This value (indicated in the formulas with λ or k) measures the material's predisposition to transmit heat: the lower the conductivity, the more insulating the material. The most insulating materials from the point of view of thermal conductivity are generally synthetic, polystyrene and polyurethane for example, which makes them valid when it's cold outside. With the sun and the heat, however, things change.
In the summer for a good roof insulation the phase shift time counts more than the thermal conductivity of the insulating material. The phase shift measures the time taken by the heat to cross a material from one side to the other; in practice it is the time difference between the time when you have the maximum temperature outside and the time when you have the maximum temperature inside. The higher the phase shift time, the more effective the material is.
Example: if the phase shift time is 8 hours, it means that the heat absorbed by the roof at 12 is transmitted to the interior at 20, when you just open the windows and take advantage of the cool evening to lower the temperature. If, on the other hand, the phase shift is 4 hours, the heat absorbed at 12 is felt inside at 16, when it is still hot outside and the windows cannot be opened, making the use of air conditioning unavoidable.
The materials with the most favorable phase shift time are usually natural ones of organic origin, for example cork, wood fiber and cellulose fiber. These natural materials have slightly lower performance in winter but much better in summer than synthetic organic materials, which makes them preferable (even if they are a bit more expensive) for a good roof insulation.
L'roof insulation it can be made from the outside of the structure, from the inside with an intrados insulation or possibly by isolating only the extrados of the last slab (insulation on the floor). One thing not to forget, especially for summer comfort, is the exploitation of passive ventilation, which can be guaranteed for example by correctly positioning skylights.