How to inspect your deck

How to inspect your deck

May is Deck Safety Month. This month it’s a great time to discuss deck inspections. Is your deck safe? This is the right time to make sure. To ensure your deck is safe, pack as many people as possible onto the deck and let them bounce in unison. If your deck doesn’t collapse, it’s safe.

Okay, it’s a joke. A professional Home Inspection in Eagan MN is the best way to find out about your deck. Building a deck is the most difficult DIY project. Replacing a water heater is another. You don’t have to hire a professional home inspector or carpenter to inspect your deck. There are some things you can do yourself.

Attachment to the House

Inadequate attachment to the house is the most common cause of deck collapses. This is why the deck below collapsed. Attachment to the house must be done if a deck is supported only on one side. Three basic methods can be used to accomplish this:

Lag Screws

Lag screws were the most popular method of attaching decks and buildings. A deck ledger board must be attached using 1/2″ lag screws. 5/16″ holes should be predrilled through the ledger joist and rim joint to ensure proper installation. Then, drill a 1/2 inch hole through the ledger board. However, you won’t be able to see the deck to verify that it was done correctly. It is best to have several lag screws and a washer between the heads. This diagram is from DCA-6.

Let’s have a little fun and see if enough lag screws were used. Minnesota residents would use Table R507.9.1.3_ to determine the spacing and instructions for installation. Anyone else would refer to Table 5 of DCA-6. Is the deck shown below equipped with enough 1/2-inch lag screws?

We need to know how long the deck joists are and the material of the ledger board to be certain. Let’s assume that the deck joists span 16′ and that the rim joint behind the ledger board is made of 1-1/2″ lumber. DCA-6 Table 5 states that lag screws should be installed every 11 feet.

Is that what we have? These joists appear to be 12″ apart in the centre. But there’s more. As shown in the diagram below, DCA-6 requires that lag screws be placed at the top and bottom sides of the ledger board.

The deck builder above didn’t know how to use fasteners differently. They ended up using almost twice the amount they needed. This deck is beautiful. Although this deck contains more information than you need, it is helpful to know where to look if you are interested.


You can attach a deck using through-bolts. They are the most labour-intensive method. This is a 1/2 inch bolt that runs through the deck’s ledger board to the house. A nut and washer are then installed inside the house. The washer and nut can be seen on the exterior. This is not an option if you don’t have access to the framing of your house. If these are done correctly, the deck’s exterior will look the same as the interior.

A washer and a hex head will be visible. The spacing requirements are not as stringent. Carriage bolts are those with round heads. These bolts were used in the past on decks but are no longer accepted. They are not intended to be used with washers, so the area that comes in contact with wood isn’t enough. This can cause the heads to crush the wood, reducing their holding power.