Decks are a challenge to any inspector.  From older decks that are decaying to newer decks that have not been built properly, we routinely find significant problems.  Many decks are poorly constructed and poorly maintained.  As a result, deck collapses are all too frequent.  Decks framing should consist of lumber that has been pressure-treated to resist wood destroying organisms.  Exterior hardware should be manufactured to be corrosion resistant (most chemicals used to treated lumber are corrosive).  Any attachment to the house should be resist seismic movement as well as be flashed to prevent water from damaging the structure.  Railings should be constructed to prevent falls.
Look carefully at these two pictures.  The metal hangers (and beams) are not aligned.  My guess is the nails used in the hardware are too small and are pulling out.  Unfortunately, the deck will probably have to be largely disassembled to find out the actual cause.  An unfortunate, and expensive problem that should not have happened.By not providing proper flashing where the ledger abuts the siding, trapped water damaged the siding.  Water should be directed away from vulnerable areas, such as ledger connections.  4x4s are not rated for horizontal loads.  This deck is located close to the ground, so when it fails, it is unlikely to cause serious injury.  Nonetheless, it is wrong.
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Home inspections in Santa Rosa, Petaluma, Windsor, Healdsburg, Sebastopol, Sonoma, Cloverdale and most other communities in Sonoma County.
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