What thickness of insulation is required for a warm flat roof?

What thickness of insulation is required for a warm flat roof?

Pitched roofing materials

The roof is the area of the building that deteriorates the most over time. Its exposure to cold, wind and rain causes premature aging of the roof. We will now analyze different ways to insulate and improve an already built roof.

By insulating the roof of a house or premises, we avoid the entry of cold and humidity, and at the same time we reduce the energy consumption of the building by reducing the emission of polluting gases into the atmosphere.

A roof is insulated by reducing the so-called “thermal transmittance”, that is, the amount of heat that is exchanged with the outside. Let’s see what methods exist to insulate the roof, commenting on their advantages and disadvantages.

The advantage of this insulation system is that the building gains in thermal inertia, i.e. the warm concrete structure keeps the heat inside the house longer and the temperature will remain stable. And consequently, the heating fuel cost is also significantly lower.

Flat roofing materials

If we have a house very exposed to the sun with large windows, the heat gain will be very high, therefore, if we apply a large amount of insulation to this house and we are in a temperate climate with mild winters and warm summers, we will be getting an oven effect inside.

A thermal bridge is an area of the house in contact with the outside where heat is transmitted because the continuity of the insulation has been interrupted, either for geometric reasons or because of a meeting between different materials.

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If a material impedes the passage of moisture, it condenses and condensation inside a house is a breeding ground for mold, bacteria and viruses. If this occurs inside the wall, where it is not visible, as a result of non-breathable insulation, we will be living in an unhealthy environment.

At Slow Home we are totally opposed to the use of petroleum-based insulation, as these are synthetic materials that not only do not allow moisture to breathe, but are also unsustainable because they come from non-renewable sources such as petroleum and require a large amount of energy for their manufacture, without taking into account that many of them incorporate toxic ingredients during their manufacture, installation or use.

Types of flat roofs

All materials have resistance, to a greater or lesser extent, to the passage of heat through them. Some have very low resistance, such as metals, others have medium resistance, as is the case with construction materials (plaster, bricks, mortars, etc.). Those materials that offer a high resistance are called insulating materials.

Therefore, the definition of thermal insulator is that material used in construction and characterized by its high thermal resistance, establishing a barrier to the passage of heat between two media that would naturally tend to equalize in temperature.

For this reason, porous or fibrous materials such as mineral wool (rock or glass wool), expanded polystyrene, extruded polystyrene, polyurethane foam, cork, etc., are used as thermal insulation.

Extruded Polystyrene (XPS) is a durable, waterproof, high mechanical performance and does not rot. Placed on the waterproofing (inverted roof), in addition to insulating, it protects the waterproof sheet and improves its durability.

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Walkable thermal insulation

There are many flat roofs waterproofed with a bituminous membrane with slate self-protection. They are usually roofs with a double membrane fully adhered to the existing substrate. The support is composed of a system of slopes by means of cellular concrete, arlite or in any case a concrete with very little mechanical resistance, since the function of this one is not other one that to facilitate the runoff of the water towards the drains.

The quickest way would be to place a filter tile over the waterproofing system. If we are going to re-waterproof the roof, by placing an element on top, it would not be necessary to use a self-protected membrane, so a bituminous membrane could be placed adhered to the existing slate. To facilitate this fusion process, it is recommended to apply an asphalt primer, after cleaning up the areas where the original sheet was hollowed out from the substrate. In any case, the filtering tile must be installed on a geotextile that protects the waterproofing membrane from possible puncturing.

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