As a homeowner, when you think of a deck, you tend to picture the exterior design and visible elements — railings, floor boards, and aesthetics of natural wood. But, the most important part of any deck is the part you can’t see: its substructure.
A deck’s substructure provides the framework that holds up the deck. It includes everything beneath the floorboards and railings that keeps your deck strong and safe. To help you understand just how critical the substructure is, I’ve addressed some common DIY questions below:
A deck’s substructure is made up of footings, posts, ledger boards and joists.
Footings provide the foundation for the deck. To build the footing, you start by pouring concrete deep enough into the ground that it goes below the frost line (the maximum depth of ground below which soil does not freeze in winter). Posts are then anchored into the concrete to provide a solid, strong structure on which you can build your deck.
Ledger boards are sturdy pieces of lumber that are used to attach the deck to the frame of the house. These boards must be attached to a solid structure. Some structures to avoid are brick veneers, overhangs, chimneys or bay windows.
Joists are pieces of wood that are used to support the framework of the deck as well. A general rule of thumb: the larger the deck, the larger the joists.
There are a few critical items to keep in mind when building a deck substructure. Firstly, always make sure you are following your local building codes. That’ll ensure you do things like make sure the footings are deep enough into the ground to provide sufficient support and that the posts on top of the footings are spaced out correctly. Typically, posts are about 6 feet apart, but it’s also worth checking with the American Wood Council (AWC) DCA6 guidelines, because everyone’s deck is different.
Depending on where you live, you can take extra precautions against water damage by applying an ice and water shield product that will protect the timbers from moisture, water or ice damage. Flashing, the metal guard that directs water away from sensitive areas, will help protect the deck from water damage as well.
Pressure treated lumber is best for the substructure. Make sure to use the correct category of treated lumber — it’s got to be rated for ground contact. Learn about the proper use categories here.
According to the North American Retail Hardware Association (NRHA), pressure-treated lumber is the go-to choice for your deck substructure, and what contractors overwhelmingly use. This is due to its load-bearing strength and affordability.
Keep these things in mind as you build:
Since it’s difficult to rebuild the substructure once it is constructed, you want to build it correctly the first time around. While this may sound like a daunting task, so long as you take into account the AWC DCA6 guidelines, your local building codes and ask a pro when necessary, you’ll have all the right tools in your toolbox so to speak!
Mark knows more about tools than anyone has a right to know. With his wife Theresa, Mark hosts the popular MyFixitUpLife talk show, is the general contractor for Food Network’s ‘Save My Bakery,’ and has been a project manager for Extreme Makeover: Home Edition, and expert guest on PBS, DIY Network, Discovery Channel, A&E, NBC’s The 10! Show, Good Day Philadelphia, and other national radio and TV programs.