7 Reasons Why Your Deck Could Collapse

Avoid making the local news by inspecting older decks.

Posted by Kevin Stevens | Oct 03, 2010
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A deck is an extension of the home and can provide some great entertaining space. But unlike a living room, a deck is subject to the whims of Mother Nature. Rain, snow and sunshine can take their toll and weaken a deck over time. Decks also need to be properly built for load, wind ratings and other local parameters to ensure a long and sturdy life. In Boulder County, Colorado, where I live, wind ratings start at 110 mph and run up to 180 mph. Snow loads start at 20 lbs/sqft in the Eastern prairie and top out at 130 lbs/sqft near the continental divide. These local parameters dictate how homes and decks are built.

Many jurisdictions follow some version of the IRC (International Residence Code) and if you are building a new deck, you are usually required to get approval and permits through your local permit office. Since most new construction will have a number of inspections, and will be based on current codes, the chances of your deck failing are pretty slim. Older decks, however, are where most problems arise. 

1. The ledger board pulls away from the house: The leading cause of deck collapse in North America is due to some type of ledger board failure. Since most decks are attached to the house via a ledger board, and not fully free standing, a failure here can be devastating. This type of failure leads the pack, in older construction the ledger board was often just face nailed to the rim joist. Newer codes required lag screws or through bolts, today special brackets like Simpson’s “DTT2Z Deck Tension Ties” are required. Newer versions of the IRC require a 1500-pound rated connector, and this is one that meets this new requirement. This bracket extends into the home and provides a solid connection from the homes floor joists through the rim and ledger boards to the deck’s joists.

2. Ledger board splits: When a ledger board is attached to a house, a staggered bolt pattern should be used. This reduces the chance that a crack will form along the length of the board, and cause it to fail.

3. Board rot: Many ledger boards rot prematurely due to the lack of proper flashing or from being built with standard lumber. All of a deck’s exposed framing lumber should be decay resistant per guidelines established by the American Wood Council’s DCA-6 publication. Ledgers should also be flashed to prevent moisture attacks from above.

4. Hanger/toe nail failure: I have seen some decks where the joists were simply toe nailed to the ledger, and others where the joist hangers were falling out due to corroded fasteners or rotted wood. Both of these problems can lead to decks pulling away from the house. On most decks this is an area that can be easily inspected and should be checked regularly.


5. Post and beam failures: Another leading cause of deck collapse is due to the failure of posts and beams. Here the leading causes are wood rot and under sized components. Posts that are set in soil, without protection, often rot to a point where they can no longer support loads. The same happens to beams that have not been properly maintained. Dynamic loads of many people out on a deck can lead to sudden and catastrophic failures, in many cases injuries and deaths are not uncommon.

6. Joist failures: This type of failure usually does not cause the entire deck to collapse in an instant, and therefore is not as newsworthy as other types of collapse. Injuries are still common as holes may cause people to fall through.

7. Foundation failures: A foundation by its very nature is supposed to be strong and durable. However, in the case of many I have seen, this is not the case. I have seen decks merely resting on rocks or blocks, set in soil or on severely undersized pads. For tall decks the failure of foundation supports can cause enough drop to occur, to rip even a properly attached ledger from the home. Uplift protection also needs to be provided at the foundation and at the deck level. Gravity may keep is looking secure now, but winds loads can lift even larger decks.

If your deck is old chances are higher that it may need some care. Proper and regular inspections are your best friend when it comes to ensuring the integrity of your deck. It is possible to make structural repairs as preventative measures. Most builders prefer to build from the ground up, but it is not impossible to work the other way. A thorough inspection and some possible repairs may keep you from headlining the 6 o’clock news.

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