House Sparrow

(1) can and will use any nest box suitable for bluebirds. They do not need nest boxes, and will nest just about anywhere. Females prefer hole-type nests over tree nests. 

(2) The nest site is selected by the male. 

(3) Nests in trees are usually globular structures with a side entrance, a squashed ball 30 - 40 cm diameter.  In trees, forked or dense branching provide an anchoring platform for nests. Neighboring nests may share walls.  See photos and here.   src

(4) "House Sparrows may raise 2-4 (average of 3) clutches each breeding season. (I thought I read a maximum of 5 somewhere.) Nests may be reused, with a re-nest or subsequent brood typically beginning 8 days after nest failure or after young leave nest (up to 10-49 days, usually 3-17). Birds experiencing failures may initiate clutches up to eight times in a nest during a single season. Some nests are reused 6 times. Cases have been seen where the eggs of the next clutch were laid while the young were still in the nest (Lowther, Bird Banding, 1979)."      src

(5) House Sparrows can easily produce three to five broods per season. As if that is not enough, male sparrows will mate with several females. With three to five eggs in the average clutch, a single pair of house sparrows can quickly become a flock of 15 to 25 birds in one season, at a single nesting site.  src