Extended rafter run for roof overhang
SkanDekâ€™s thin steel bearing rafters are of course suited to roof overhang construction. Normally the roof elements can be run out by between 2.5 and 4.0 meters dependent on type and stress loads. Elements can be supplied with corresponding jack rafters on the side of the box roof, creating overhang in, for example, gable end construction. Jack rafters can typically have an extension length of 0.5 meter, though the strongest types can be extended up to 1.0 meter.
Structural design of roof overhang
The patented bearing rafters within the box roof system are constructed of light gauge steel profile plating that, put together, make up the beam. The two halves can be displaced, creating an overhang of thinner dimension. Builder or architect can themselves choose either top or bottom extension of the beam.
Project planning of the overhang
During the project stage of the planned overhang, there are multiple points to take into consideration:
- Extended building elements in heated buildings should be insulated against thermal bridging, resulting in heat loss and condensation in and on the inside ceiling. Moisture can result in damage to the building elements due to damp and poor indoor climates. SkanDek therefore recommend, that the extended light steel plating be insulated with a minimum of 30mm insulation.
- During installation of the soft mineral wool between casings as thermal bridge insulation a wind shield should be established, so that the wool is not ripped or damaged by wind. The shield can then be sealed using a suitable grouting.