Installing A Deck Footing On A Slope

What's a good Rule of Thumb when footings are on a slope?

Well, there is a general rule for deck footings on a slope and it's based on average soil conditions. So if you have unstable soil conditions all bets are off. You will want to speak to an authority in your area. Usually a geo-technical engineer or someone with lots of experience in your local building department building decks will know exactly what to do.

The Seven Foot Rule is a great rule of thumb to be safe. It's simple to remember and for most conditions quite conservative.

But don't push it. If you are on a mountainside with tons of rain in the winter months, do speak to someone is professionally qualified.

Otherwise you are flirting with disaster.

Simple enough thought.

As you see here any footings on a sloped grade like this should be quite safe as long as there widest point of the footing is no closer than seven feet from the slope if you project a horizontal line at from the point of the underside of the footing.

Be Safe Rather Than Sorry

The footings your deck rests upon are the most important part of your deck.

This is only a rule of thumb.  Any slope has to be examined and understood before any building should upon it.  There are places in the St. Lawrence Valley, and Alaska where quick clay or leda clay as it is sometimes called, is present.

This a potentially very unstable soil at the best of times.  A water laden slope would be at high risk of literally washing away under the right conditions.

Alternatively in mountainous terrain soil can be a mix of sedimentary layers or alluvial rock or sand.  This kind of slope is also at risk of sliding if its saturation point is reached.  The seven foot rule may not apply in any of these situations.

Know Your Soil Type Before You Dig Your Footings

The topic of foundations and how to properly support a deck over a sloped grade demands some local building knowledge that you have to acquire before you build or plan any light structure.  On special locations like slopes or hillsides, take the time to contact your local building officials to find out what the soil is and what are common building practices.

Obviously a hillside deck can give you dramatic views and benefits but don't forget safety in the equation.

Some Other Great Reading...

Different Styles of Footings on Flat Ground


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