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Inspecting Single Ply Beams

Although a visual home inspection is not a code or engineering inspection, many home inspectors would require that beams and wood support members are multi-ply or built up beams. Commonly 2 – 2 by’s and a ½” piece of plywood sandwiched in the middle. Single ply beams would not be appropriate for door and window headers, or for spans supporting a second story or roof structure. Currently single ply beams are only acceptable for decks, porches and landings where no additional support is required. In the 2018 IRC, there is now a span table specifically for decks (Deck Beam Span Length’s for Single Ply Beams), the table is above. The table specifically addresses 2×6 – 2×12 single ply beams for deck joist spans. Using the table we can see a single ply 4’ 11” 2×6 can support spans up to 6’. A single ply 5’1”  2×8 can support spans of up to 8’. So what should a home inspector look for:

  • These spans also apply to stair landings not supporting a second floor or roof structure
  • This table applies to decks / porches and landings not supporting a second story
  • Roof structures that are being supported by a deck will require a larger beam / support member
  • Single ply beams are used for small spans
  • It is acceptable to use a single-ply beam in place of multi-ply beams as long as the size is appropriate
  • Single ply beams can be used for space requirements are an issue
  • Single ply beams will also save money

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