The easy way is this; put villagers on each ruined hut, until a scaffolding is built. (If they 'look confused' you need more restoration.) The laundry hut is the only one they will work on all by themselves; the population huts get worked on, apparently, only as the population begins straining; my villagers left my population hut at 1% long after they completed every other building project with only minimal assistance from me.