Oh bugger! A chewer!

Really annoying for you I can imagine.
Several reasons, why a dog might chew things. I suppose some of the things to look our for to detirmin why are,
1. Your reaction when you catch him in, or after the act. To a dog, actions can be reinforced by a negative reaction on our part as well as positvie reactions. Assess what you do or say to him when you come home and he has torn things apart.
2. Have you considered the possibility of seperation anxiety. It often rears itself by barking, pacing or damage of items around the home when the family is away.
3. Too much freedom, is it worth considering reducing accessablitiy around the home to only a very small, safe area when you are not around to supervise, or maybe even crate training?
4. Boredom without family company around, particuarly if he is quite used to your company, to be without it for a period of time, and without the stimulation of you around, it could be a time passer for him until you do come home.
5. Dont rule out the possibility of it just being a habit that he has just fallen into.
Just a few thoughts anyway, good luck with it, I hope you work out why soon, so you can start preventing it.