by Nick Gromicko, CMI®, Founder, International Association of Certified Home Inspectors (InterNACHI)
- More decks collapse in the summer than during the rest of the year combined.
- Almost every deck collapse occurred while the decks were occupied or under a heavy snow load.
- There is no correlation between deck failure and whether the deck was built with or without a building permit.
- There is no correlation between deck failure and whether the deck was built by a homeowner or a professional contractor.
- There is a slight correlation between deck failure and the age of the deck.
- About 90% of deck collapses occurred as a result of the separation of the house and the deck ledger board, allowing the deck to swing away from the house. It is very rare for deck floor joists to break mid-span.
- Many more injuries are the result of rail failure, rather than complete deck collapse.
- Deck stairs are notorious for lacking graspable handrails.
- Many do-it-yourself homeowners, and even contractors, don’t believe that rail infill spacing codes apply to decks.
This document does not address specific building codes, balconies, lumber species, grade marks, decks made of plastics or composites, mold, or wood-destroying insects.
Required Deck Inspection Tools:
- measuring tape;
- plumb bob;
- probing tool; and
Optional Inspection Tools:
- moisture meter;
- magnet; and
The image above depicts notches in a supporting beam. Notches must be less than one-quarter the depth of the member. On the tension and compression faces, the notch depth must be less than one-sixth of the member’s depth, and the notch length must be less than one-third of the member’s depth. Notches are not permitted in the middle third of spans, or on the tension face of members that are greater than 3½ inches thick.
- joist length;
- type of fastener;
- diameter of fastener;
- sheathing thickness;
- use of stacked washers;
- type of wood species;
- moisture content;
- band joist integrity; and
- deck loads…
On-center spacing of ledger fasteners in inches = 100 ÷ joist length in feet.
The image above depicts both over and under ledger board flashing. The ledger board should always be flashed even when the home or building has a protective roof overhang.
The image above depicts a cantilevered deck. Joists should be cantilevered no more than one-quarter of the joist length and three times the joist width (nominal depth). Both conditions must be true.