Decks Can Be Dangerous

Deck failures are becoming more common. Why do decks fail?

The most common reasons are:

  • Old age
  • Poor design
  • Improper materials
  • Overloading

Decks should be inspected annually. All lumber should be inspected for rotting, particularly where posts meet the ground, at joist unions, and the ledger board connection to the house. Most of this rotting is caused by old age, moisture, and lack of maintenance.

However, much of the rotting is coming from fasteners and connectors that are incompatible with the type of wood preservative the deck lumber was treated with. Rusted heads on nails, screws, or bolts connecting metal joist hangers are an indication that these fasteners or connectors have failed. This was caused by a chemical reaction between the metal hardware and the pressure treated wood. This form of failure is the number one reason for decks collapsing.

Unfortunately, there is great confusion as to which fasteners and connectors are to be used with what type of lumber. The best choice is stainless steel, but it is also the most expensive and difficult to obtain. The most commonly used nails, screws, bolts, and metal hangers are hot dip galvanized. These are a good, available, and lower cost choice. The thicker the galvanized coating the better and longer the metal hardware will perform. Other approved materials, similarly priced to hot-dipped galvanized, are silicon bronze and copper.

Deck collapses are often related to overloading or lateral movement. This two conditions place a great amount of stress on the deck fasteners and connectors. Therefore, whenever rust is seen on nails or screws, they should be removed for inspection or replaced.

Avoid a disaster inspect your deck each year.

Doug Hastings
MN Home Inspector, Minneapolis & St. Paul
ASHI certified inspector, ACI
Kaplan University, Home Inspection Lead Instructor

Rob Leslie
Kaplan Professionals, Retired

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