Building cantilevered decks or balcony decks without support posts is a controversial subject in the deck building world. Most professional deck builders try to avoid building these types of decks because of the risks involved. We do not recommend that DIY builders attempt building a cantilevered deck on their own. The primary concern is that in extending the deck framing into the house wall you create multiple openings for water to penetrate the wall. Proper flashing and sealing each opening is crucial because blocking is used to fill the gaps between each joist bay. An improperly installed cantilever deck can lead to thousands of dollars in damage to your house or an injury caused by a collapse.
Hiring an Architect or Engineer is usually a requirement for getting a permit to build a cantilevered deck. This will ensure the deck structure is properly designed and compatible with your house construction. The allowable cantilever will depend on the size of joists you are using, the spacing of the joists, and the connections to the house framing. As a rule of thumb you may be allowed to cantilever the deck joists 1/3 of the total length of the joists. As an example if you wanted a 5' cantilever you would be required to use a 15' joist and attach it securely back 10' into the house. Some cantilevered or balcony decks use custom steel angle brackets to hang the deck off the house frame.
