Factory-produced roof elements consist of rafters (usually double rafters), insulating material, underlay, ventilating lath, vapour barrier foil and chipboard or OSB board to provide the element with the necessary rigidity. The constructive solutions for the top part of the roof element are different depending on the roof covering – tiles, sheet metal or rolled roofing material.
The rafters are calculated based on load bearing capacity and sagging. The choice of rafters depends on the width of the span between the ridge beam / load-bearing internal wall and the external wall. For the rafters we use solid wood, solid wood compound beams connected with nail-plates, I-beams, laminated timber or Kerto-wood. The use of double rafters is most common in roof elements.
The maximum width of factory-produced roof elements is 2.4 m and the length is 12 m. The maximum dimensions of the elements are primarily based on restrictions arising from transport equipment, but work safety at the factory and on the construction site also needs to be considered.