I am little confused. Some pictures in this forum, and books, as well as at beesource shaw the board with the slats perpendicular or pararel to the frames. What is corect? I am planing to make them myself this year, and I thought they should be pararel.
Pre-varroa, the standard method was perpendicular to the frames, possibly because it is easier to build. Now with varroa, the standard seems to be parallel to the frames and placement under the frames (ie. 9 fames/9 slats or 10 frames/10 slats). The reason beeing that with the slats under the frame, the chances of the slats catching falling varroa is minimized. This is especially important when using screened bottom boards. If you are not using them as part of IPM, but more for ventilation/bearding/swarm control (the original intent), than either way will work.