Labrador pup biting ?

We have a golden labrador pup only 18 weeks. We thought his teething may have calmed or at least thought it would help by giving him teething stick toys etc. The pup has his own room where he sleeps and where we keep his food water toys bed etc. However he has completely chewed the whole way through the walls in his room the the point the concrete is chewed of as well as the wallpaper and it will be very expensive for us to fix and will need resurfaced he has chewed that much. He also has dug up the whole entire back garden which is awful looking we know this Is a pup, but is there anyway we can help with this or give him anything or will he grow out of it as its just teething. It isnt fair on the dog either as we can no longer leave him alone in other rooms and we feel bad we keep him in the one room, obviously we do walk him etc and allow him in the other rooms of the house whilst we are there. Thanks