Can an Upper Level Wood Deck Be Extended?

Existing Deck

• Regulations for deck construction may have changed for certain structural elements of an existing deck. Specifications for joists, posts and beams have changed, and innovations for footings have been introduced. The structural condition of the existing deck may also have deteriorated. A thorough visual inspection of the deck should be conducted before adding to it, and the current building regulations should be carefully reviewed. Structural design for upper decks must be carefully planned, as failure of the deck has serious consequences.

Upper Level Deck Construction

• Support for decks is usually based on post-and-beam construction, but upper decks are often cantilevered — supported on only one end — for aesthetic reasons. The support may be provided from joists extending through the wall of the building to carry part of the length of the deck. The length of the unsupported portion is set according to the loads the deck is carrying. The cantilever structure is subject to moisture penetration, which affects the lifespan of wood.

Post-and-Beam Construction

• An upper deck may be extended through standard post-and-beam construction, or structural support may be added under an existing cantilevered deck and the extension cantilevered instead, as regulations allow. In order to comply with regulations, the supporting structure of the existing deck may need an upgrade because of additional load-bearing requirements imposed by the extension. The existing supports may have deteriorated, as well. Bracing may be necessary, depending on the design of the deck.

Deck Building Regulations

• The International Residential Code addresses standard deck construction, but building officials often face deck designs other than those contained in the IRC. Other agencies, such as the American Wood Council, have developed more detailed deck construction recommendations that are considered equivalent to IRC code. Review existing standards for deck construction when contemplating an extension to the upper deck. Consider whether the existing structure can be adapted to accommodate the additional weight, and comply with current building and engineering practices.