Lag Bolting Your Deck

Insurance companies seem to be cracking down on decks that are not properly lag bolted to homes.

Is your deck lag bolted properly?

The most common cause of deck collapse is improper attachment to a building.  Most decks are supported on one side by the building, and on the opposite side by the earth.

The photo below shows improperly attached deck collapse:

Deck Collapse

The piece of wood that connects a deck to a building is the ledger, or ledger board.

Lag Screws

Lag Screw

Traditionally, lag screws are the most common method of attaching decks to buildings.  To properly attach a deck ledger using 1/2? lag screws, 5/16? holes need to be pre-drilled through the ledger and rim joist.  After that, a 1/2? hole should be drilled through the ledger only.


Lag Screw Diagram

Sometimes lag screws are not attached to anything substantial behind the ledger.  When a home is constructed with floor trusses and there is no rim joist for the deck to attach to, it’s important to figure out what the screws are going in to.  In the photos below, the lag screws were only attached to the fiberboard wall sheathing.

Lag Screws at ledgerboard

Lag Screw in to nothing

Lag screws are inexpensive, but they’re an important part of installing your deck properly.

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