It is on record that nests specially built in mid-winter have then been used for communal roosting, providing a warm refuge from frost and snow. One such nest constructed in a cotoneaster was quickly packed to capacity. It became so full that the tail and rear end of the last wren to enter protruded from the entrance. During severe weather, one nestbox roost held 60 wrens. The occupants took between a quarter and a half hour to enter at night and twenty minutes to disperse in the morning.
Some roost sites are traditional, drawing birds from more than a mile away.
Once inside, roosting wrens squat up to two or three layers deep with heads facing inwards and tails towards the entrance or sides. The largest roost of which I am aware was situated in the loft of an isolated house. The birds entered through a hole in the fascia just under overhanging roof slates. Accurate counting was difficult as birds continued arriving until almost dark. On occasions they needed to line up before entering-running the gauntlet of a highly aggressive wren at the entrance forcing some to go elsewhere.