Excavator: Dead wood. Females construct the nests in rotting and decaying wood in a variety of sites, such as beams, stumps, boughs and occasionally in door- or window-frames. The brood cells are made of cut leaf fragments of Betula, Fagus, Acer, Rosa and Epilobium (Celary, 1995; Celary & Wisniowski, 2001).
This is supported by observations in Norway (Sydenham 2015, pers. com)
Banaszak & Romasenko (1989) contradict this, and state that the species nests in existing cavities in dead wood or in the soil.