Often when I'm raided, all or most of my buildings would be destroyed. When I raid, I barely deal any damage to barricades with firearms. I don't think melee weapons perform any better. Explosives do work, but they're rather uncommon to come by. So how is it done?
After much experimentation and asking on the chat channels, it appears that melee weapons actually are the best way to destroy buildings. On raids, it's nice to give your medic or other noncombat-oriented survivor a melee weapon to break down barricades.
Melee weapons deal damage to barricades according to their stated damage. Thus, a 50 dmg chainsaw deals the same as a 50 dmg katana, in spite of the intuitive leaning towards using a chainsaw for building destruction.