It sounds like your boy has developed separation anxiety. It is not uncommon in dogs and can develop at any age. It occurs because he is separated from his humans and it happens if other dogs or animals are there or not. The good news is that there is techniques that you can use to help combat the problem.
First thing is to take your dog for a nice long walk before you leave, preferably 30 minutes or long. Make it a long, quick paced walk to tire your boy out. A tired dog is less likely to be destructive. Another thing you will want to do is to use a low-key approach to leaving the house. Ignore your dog before you leave and after you come home for at least 5 minutes or more. If your house is like mine in the morning everyone is running around getting ready to leave. This has the dog in an excited mood and then suddenly you are gone. If this is the case, put him away from everyone, say in a bathroom until the frenzy is over.
Don't punish or shout at your dog when you come home and find he’s destroyed something. When you do, you increase his stress level rather than reduce it. You can provide him with small stimulating toys or toys that you can fill with treats. I like the kongs with treat compartments. You can fill them with peanut butter or yogurt and freeze it. Once frozen you give it to him and it takes hours for him to get everything out of it. If he's busy gnawing on the kong, he won't be gnawing on the doors, windows etc.
Sometimes leaving a TV or radio on can help a dog with this problem as well. I have many clients tape the noise of them taking a shower and have them play that on a loop when they leave. Now the dog knows you are gone, but the sounds that he associates with you being home but away from him tend to help a little. Also remember to not reward a dog's excitement to you with petting and affection or even eye contact. You want to show him nice calm praise when he is being calm. So when you come home and he's excited, ignore him until he is calm. Then praise or love on him.
The best way is to crate him. This prevents injury to the home and protects him as well. Dogs can be crated for long periods of time and with a small dog like this, you could have a pad in with him for elimination purposes. Another thing that might help is a DAP collar. These use a pheromone to calm a dog. Since the DAP collar is not a medication, it can also be used in conjunction with meds as well. See one here:
Practice putting him in the crate, leaving the house, opening the door immediately and rewarding him with a hot dog treat if he did not scratch, bite and carry one. This desensitization teaches him that you leave but come back quickly. Once he seems to not do anything when you initially leave, lengthen the time he must be quiet and calm before youwill come back in. Change the time as well. Make it 2 minutes one time and 10 mintues another, so he never knows if you are gone for an hour or gone for 2 minutes. It helps him stay calm for longer periods of time, just be sure you reward him when he is good. This takes a lot of work but is very effective. At one point you will need to actually get in the car and get back out or ride around the block. He has to hear the same noises he would if you were leaving normally.
Another thing that helps is to do things that might make the dog feel you are leaving and then don't such as putting on your coat or picking up your keys. Or leave without doing those things. This helps remove things that might trigger the dog to become anxious even before you are gone. I know some clients that keep a coat inside the car so the coat doesn't trigger the anxiety.
These should help his separation anxiety and help curb the destruction. It will not be an overnight cure and will take work on your and your family’s part to be consistent in your interaction with him. Here is a site that also offers idea to combat separation anxiety.
Now you could also put decorative sheet metal on the lower portion of your doors to prevent the destruction as well and they do make scat mats (available online and in pet stores) that could be used in front of doors and on furniture to prevent a dog from getting to a window. These might be an aid to use to keep destruction down, but I see that you just posted that he destroys carpet as well, so it wouldn't work too well to prevent that type of damage.
Another option is medication, which is discussed on the following site. Your vet can get you a prescription which is often helpful. Many owners combine medication, dap collar and desensitization training at first and slowly wean their dog off medication as his anxiety level decreases.
Hopefully I have given you a lot of techniques to help combat your little ones problem. Definitely add the sheet metal to the outside door to stop his scratching up the outside door and screen. I have it on my doors for not only dogs scratching but cats tearing up the screens. They do make something called softpaws that might help reduce the severity of the damage done by his claws, but you can't declaw a dog. Here is the site for the claw covers.
I hope this information is helpful to you. If you would like any additional information or have more questions please don’t hesitate to press the reply to expert or continue conversation button so I can address any issues you still have . If you do find this helpful, please take this opportunity to rate my answer.