There are various methods to insulate the roof structure from the outside. External roof insulation is applied when interior insulation has already been installed and all painting and finishing works are completed, but there is a need to improve the quality of insulation.
Adding an additional layer of insulation from the outside is a simpler and more efficient solution. Moreover, exterior insulation is preferable when the insulation thickness needs to be increased without reducing the headroom space in the attic.
Benefits of External Roof Insulation
This solution is often used for aesthetic reasons, particularly to maintain a rustic look with visible roof beams. Additionally, installing insulation from the top creates a more homogeneous barrier without thermal bridges, which can prevent condensation issues. Although the procedure for installing external thermal insulation differs from internal insulation, and other types of insulating materials are used, the advantages are clear.
External roof insulation can be done using both stone wool and EPS (expanded polystyrene) boards, but products specifically designed for this purpose must be selected, which typically have higher density and greater rigidity. Pitched roofs are more durable than flat roofs, but it is essential to consider the mechanical strength and point load resistance of the insulation layer. The insulation must withstand snow loads and occasional roof access for minor repairs or cleaning. Therefore, insulation with greater strength is required than that used for internal applications.
Insulating with Stone Wool and EPS Boards
All reputable insulation material manufacturers offer stone wool boards designed for roof insulation. For example, Rockwool provides Dual Density stone wool boards, while Knauf offers Thermotop panels. When it comes to EPS boards, Austrotherm offers high-strength EPS A150 boards suitable for external roof insulation.
The procedure is similar regardless of the manufacturer or type of insulation used (stone wool or EPS boards). If the old insulation is worn out, it is completely removed, and a new vapor-permeable membrane is carefully applied to perform its function correctly. Standard stone wool is placed between the rafters, and once the space between the rafters is filled, rigid stone wool boards or EPS boards are installed on top.
Vapor-Permeable Membrane is Essential
Depending on the type of attic, it might not be necessary to remove the existing insulation between the rafters. Often, the insulation is either new or in good condition but does not provide sufficient thermal insulation. In such cases, rigid stone wool boards are laid over the existing insulation between the rafters.
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After that, a secondary layer of vapor-permeable membrane is installed over the stone wool. Longitudinal battens are then placed over the insulation in the direction of the rafters and secured with long screws that pass through the insulation to the rafters. Standard horizontal battens are nailed over the longitudinal battens to which the roof tiles are attached.
Double Battens Provide Dual Functionality
Longitudinal battens primarily provide a fixed support for the horizontal battens. Additionally, this construction ensures an air layer between the roof tiles and the insulation, which allows air circulation. This is particularly useful during the summer months, as it significantly reduces the transmission of high temperatures to the insulation and subsequently to the rooms in the attic.
Photo: Rockwool, Freepik