What is this insect that seems to hatch from OSB?
Looks like a type of Lacewing. Their larvae are predatory, mostly eating smaller insects like aphids and other insect larvae. If you are seeing the adults, it's likely that the larvae were pupating over the winter in a cozy spot between some boards. Although I have never heard of the larvae pupating in large groups, it could be that something about the structure was very attractive for the purpose. Since they eat aphids, most people consider them a beneficial species when they are in the garden. Maybe not quite the same if your house is full of them. Do you have any house plants with aphids?
Lacewings should not be harmful to the structure, but they could be feeding on something else that is. There is a species in the US that reportedly feeds exclusively on termites (destructive). There are other species that reportedly feed on spider egg sacks (nondestructive). With more than a 1000 species identified around the globe, and new ones still found from time to time, there is likely a species for every food source and likely a food source for your species either in or in very close proximity to your home. They are also attracted to lights, so if you leave lights on overnight they are likely to swarm around if conditions are favorable.