He specifically worked on the detailed drawings for the large rose window on the western front of the cathedral.

He also undertook valuable work in arranging and systematizing the sculpture and stone collection, with archive cards, drawings, and photos of each fragment.

After Nordhagen's death, Tverdahl was appointed as the acting artistic director of the project from 1926 to 1930.

In 1929, he participated in the architectural competition for the last portion of the restoration of Nidaros Cathedral, which was won by Helge Thiis.

He collaborated with Thiis, who wanted to benefit from his building archeological knowledge and made sure that he got his own office during the restoration.