If your summer home improvement plans involve building a new deck, congratulations! Decks are a great addition to any home and provide a lovely place for entertainment and relaxation. Before you get started on building though, it is crucial you have the proper foundation in place first.
Depending on where you live you may need to get a permit or even an inspection, so keep that in mind and check with your local city or town hall before you break ground. A strong foundation is the key to a long-lasting and more importantly, safe deck.
The Basics
A deck foundation needs to be able to safely transfer loads from above to the ground below. Since deck foundations are generally isolated rather than a connected slab like a home foundation, they have only the soil surrounding them to rely on for stability. Fortunately, decks aren’t usually asked to carry heavy loads, but there are things you need to do to ensure safety and comply with building codes.
First, you need to figure out how much of a load each post will need to carry. The formula for this is the area of the deck the post will be supporting times the combined live and dead load, which in most cases is 40 psf and ten psf. To figure out the area the post will support, divide the joist and beams spans surrounding the post in half. If this seems terribly complicated, you may want to have a certified contractor or builder do the job.
The International Residential Code (IRC) is what you’ll want to follow when building your deck. If your deck is going to be supported by your house, you will be required to use special hardware to connect it to your home. Check your local building codes to see the exact requirements for your area.
In almost all areas of the United States, your deck foundation must extend past the frost line. Depending on where you live that could be anywhere from 36 to 70 inches below grade. This is to avoid damage from frost heave and keep your deck stable. Check with your local code compliance officer to find out the exact frost line for your area.
Special Considerations
If you live in an area of the country where things like earthquakes or tornadoes are a concern, you will have additional code compliance requirements to ensure your deck’s safety. In fact, if you live in an area like this, a ground level deck rather than an elevated one may be a better choice. No matter where you live, you will be required to set the ends of your posts into concrete blocks buried at least a foot below grade. Don’t rely on the soil alone, even if it’s tough clay. It’s not enough, and wood inserted into the bare soil is at high risk of rot. Always make sure the posts are reinforced with concrete.
The wood you use for the posts is also important. Always use pressure treated wood and when you are choosing lumber, try to get pieces with as few burls and other flaws as possible. Why they may look nice on a floor or wall, they can weaken the wood. Never skimp on lumber, buy the very best you can afford, and treat it with a waterproofing stain to keep it strong and looking good.
A new deck will add beauty and value to your home and provide hours of entertainment or relaxation, but it’s crucial to ensure it has a solid foundation first. We’ve all seen stories of deck collapses on the news. They cause countless injuries and even deaths each year. To avoid adding to the statistics and keep your deck sturdy and beautiful for years to come, make sure you follow all building codes and safety requirements to the letter.