Some of the more common deck construction mistakes that I see are:
• Missing or Improper deck flashing - Flashing prevents water from entering behind the deck and into the structure. Flashing is required where decks attach to a wall or floor assembly of wood frame construction.
• Insufficient Deck Ledger Connection - Deck ledgers must be bolted or lagged to the house in order to develop sufficient structural capacity.
• Improper Size Handgrip - The handgrip for a non-circular cross section must have total perimeter dimension of at least 4 inches but not more than 6.25 inches.
• Guard opening limitations - Deck flooring elevated 30 inches or more above grade shall have guardrails with intermediate rails or ornamental closures which do not allow passage of a sphere 4 inches or more in diameter.
• Insufficient floor joists supports - Joists framing into the side of a wood girder shall be supported by approved framing anchors or on ledger strips not less than nominal 2 inches by 2 inches.
• Improper Foundations - Decks must be built on suitable foundations capable of supporting the load and accommodating environmental forces
• Decks Improperly supported on brick veneer - Masonry veneer shall not support any vertical load other than the dead load of the veneer above.
The code load requirement for residential decks is 40 pounds per square feet (psf) live load, which represents the weight of the people and moveable objects, such as planters and deck furniture, that use and occupies the deck. Assuming a 12 ft. by 12 ft. deck and that the average weight of the occupants is 150 lbs, the deck would safely support 38 adults.
It is practically impossible to overload a deck designed and built to the 40 psf live load requirement. The danger rests in the fact that the majority of decks and porches were not built correctly, making a crowded deck party a dangerous situation.
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