Decks can, and sometimes do, collapse. It can happen at any moment, and often when you have several people relaxing on it.
The good news is that most homeowner’s insurance considers a deck to be part of the structure of the main dwelling. Thus, your deck will be covered in exactly the same way as the rest of your home.
However, you are responsible for maintaining the deck and if the collapse is caused by damage that would have been avoided with proper maintenance then you will likely be denied. Furthermore, if your deck was built without proper permits or not to code you will not be covered.
If you are adding the deck or it is a recent addition, you should let your insurer know—even though it is considered part of the main dwelling, it is a new part and if they are unaware of it they could deny a claim.
Your policy will outline all the coverage you have and any specific-item coverage. But remember, don’t wait for the worst to happen to find out you’re not insured. If you’re in any doubt, talk to your broker—you can add coverage or change a policy at any time.