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Insulation of Sloped Roofs
At least 60% of all heat losses occur through the roof structure. This is natural, as warm air rises. Therefore, the role of insulation in a sloped roof structure significantly increases compared to other applications—any damage to the integrity of the insulation blanket in the roof assembly will result in through-freezing.
However, besides the insulation itself, several key elements are present in the sloped roof structure, which ensure proper insulation performance and help maintain its condition throughout the structure's service life. These include vapor barrier film on the indoor side, under-roof waterproofing on the outdoor side, and in some cases, a film preventing condensation from forming on the inner surface of metal roofing.
Types of Insulation Materials for Sloped Roofs
Most commonly, insulation for sloped roofs is made from fibrous materials based on glass wool or basalt wool. Both materials are produced by melting raw material mixtures. In the first case, it's sand and recycled glass; in the second, it's gabbro-basalt rock and slag—a byproduct of coked coal combustion in a blast furnace.
Insulation materials are available in board and roll forms. Each has its advantages and disadvantages. For example, roll insulation is quickly installed and provides a uniform insulation blanket without numerous joints—thermal bridges that cause heat loss.
On the other hand, on roofs with steep or very shallow slopes, board insulation is often more convenient to install. Standard board sizes are 610 x 1000 mm or 1100 mm, so each roof slope may have several joints. To minimize the negative impact of these thermal bridges, multi-layer insulation is recommended. For example, with a recommended insulation thickness of 150 mm, it's best to apply insulation in three 50 mm layers or two layers—100 mm plus 50 mm. Having two or more layers allows for staggered joints, breaking thermal bridges.
Installing Insulation in the Truss System
The main rule when installing mineral wool in any framed structure is the width allowance rule. It states that the insulation material’s width should be selected with a 1.5–2 cm surplus. Thus, insulation is installed tightly. Mineral wool boards or rolls are held in place by the fiber’s quality and properties, particularly its elasticity and resilience.
It’s commonly believed that there are so-called recommended densities for use in different structural designs. In reality, insulation density has absolutely no relevance in material selection. Consumer properties of insulation materials include thermal conductivity, compressibility, fiber elasticity, and material vapor permeability. These properties determine the material’s suitability for a specific construction.
