Installing the decking joists the will provide the framing platform for the deck boards is the seventh step in our series on building your deck. Before you can install the joists, the ledger should be in place along the house and the girders should be secured to the posts. The joists will be anchored to the house via the ledger and then supported by the girders. Take careful measurements, cut carefully, and be sure that your joists are very sturdy before moving on to the next steps. For complete, step-by-step instructions for this DIY project, watch this friendly and straightforward video tutorial.