There is always the danger that a deck could collapse, which would bring about so many injuries. You will see decks and porches in almost all houses you visit. These shall grow weak as time passes. If nothing is done about it, they become a health hazard. You need the deck frequently inspected to keep the chances of accidents minimal. You can also tell when you need to replace it or have it repaired. These are some of those signs.
If you notice the railing is unsteady, you need to worry. Railings are normally attached for beauty as well as safety purposes. They are what prevent many of us from falling off the deck. IF they start wobbling, they will not do their job well. Fastening the railing will not help, since it is the base that is the issue. The deck will have started to rot. While you wait for the replacement work to start you need to warn people against leaning on it.
Unstable joists are also another clear sign. These are what keep the deck together and hold it up. Wooden joists need to be checked for damage, rotting or sagging regularly. You need to be thorough with the inspection, and not just look at them. When the wood gets soft, a replacement shall be inline. There is also the danger of a termite infestation. You cannot hesitate to call in the professionals at this point.
After some years have passed, a replacement job shall be mandatory. You need to do so even if you had given it the best care possible. You may have also gotten the house with a deck that had not been replaced for a long time. Either way, that deck may be past the building code regulations. It does not hurt to find out what the local building codes are for such an installation. You could also ask this of the decking company you are negotiating with.
You will also tell when it is time to replace a deck by checking if it sags when you walk across it. There is no better inspection you can do.
You may need to also check out the posts that support the deck. They are the support to the joists on which the deck is held up. It is important that they remain secure in their position. When they start to wobble, it shall be dangerous to keep using the deck.
You may also call in the professionals when you are not sure if you need the replacement. You may have trouble readings these signs accurately. This makes their input even more critical. What they find out will be important to your safety.