It depends on the final design and what you have to work with. The existing material should be inspected by a professional to verify that the structure is sound and can handle any stresses the proposed extension will impose on it. The ledger board is of particular importance: it’s the point where most decks fail.
If you don’t want to reevaluate every ten years or so, consider cellular PVC or aluminum. It will cost more initially, but their longevity makes them a good investment in the long run.
Railings are a key safety feature. Wood railing upgrades and/or replacements should be considered every five to ten years, whether or not a deck expansion is in progress. Aluminum or vinyl railings weather much better and are excellent replacement materials.
If you have more questions about decks or other subjects we’re happy to answer them. Call 613-736-1122 or hit the chat button on the right during business hours.