Answer Peripheral and expansion joints are required for any screed, with or without radiant heating! German standard DIN 18560, part 2 “Screeds and heating screeds on insulation layers” explicitly, states the following: “The screed joints drawing must be provided by the construction designer…”. Within the heating screed’s surface, 3 types of joints must to be taken into consideration. Peripheral joints must be equipped with edging strips along enclosing walls or other building elements, such as door frames. Edging strips should absorb the extension of the screed body and provide sound protection for other parts of the building. Expansion joints filled with elastic material within the screed fields separate the screed at their full diameter and absorb length extensions. Shrinking joints are cut into the freshly mounted screed using a trowel at a maximum depth of about 1/3 of the layer. The shrinking joint provides stress release during the screeds drying period. Afterwards, these joints can be closed as long as they are not in a door area. In such a case, the shrinking joint should be moved up to the floor surface. It is important that a joint plan be formulated for the radiant heating system in order to adjust the heating loops to the joint areas, since expansion joints can be crossed by supply lines only. At this point, the heating pipes must be equipped with protection pipes or coatings of ca. 30 cm. The extension joints must be transferred to the floor covering. An early stage clarification of the joint layout is required if the floor covering should consist of stone plates or tiles, since the arrangement and mounting of these affects the joints’ position.
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