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Are you looking for particularly efficient, clean insulation for your roof? If so, rafter insulation is the answer. You simply place hard or soft insulation boards directly on the rafters and fasten them from above using a batten construction. This has the advantage that the insulation boards create a continuous layer, thus preventing thermal bridges. It also means that no room height is lost inside, since the insulation lies on top. This offers particularly efficient energy saving. However, the outlays for this project are by no means cheap – because the entire roof has to be completely re-covered, it is a good idea to opt for rafter insulation, especially if major renovation work is planned anyway.
What else should be kept in mind?
Rafter insulation causes two particular types of forces to be exerted on pitched roofs, which fasteners must absorb. On the one hand, shear force, which occurs because the insulation naturally wants to slide down the rafters. On the other hand, the suction force of the wind, which tries to lift the insulation complete with covering off the roof in the lee. In order to withstand both forces, screws are required that reliably stop the shear forces and hold the rafters and battens together even in the strongest of winds.
Another thing that needs to be considered with soft insulation material is that normal screws would cause soft insulation to be squashed between the rafters and battens, rendering much of its effect useless. In order to prevent this, you need a screw with a shank geometry that holds the lower screw thread securely in the rafter, has a smooth shank inside the insulation and is equipped with a fixing thread below the screw head to ensure spacing between the battens and rafters. SPAX with partial thread are suitable for hard insulation.