The tristate/Cincinnati area is blessed with a landscape that some have compared to cities like San Francisco. Historic architecture nestled amongst our rolling hills can be breathtaking. But these same hills also pose unique challenges for new construction.
So…What makes a hillside addition different than one on level ground?
A garage or any structure built into a hillside like this must also function as a retaining wall. A hillside foundation wall is in a constant battle with gravity and the weight of everything that is above and behind it. Add pressure created by the weight of water to this mix and you need a wall with some serious strength. This all means that the correct steel placement, wall and footer size as well as drainage must all be designed by a licensed structural engineer.
Hughes Construction installed this particular garage addition with the plans provided by Schaefer Engineering.
In order to retain the pressure of the hillside surrounding it, the design specified that we pour the rear wall 12″ thick and the side walls 10″ thick. The footer also had to be enlarged in order to support the weight behind it.
The size of the footer and rebar placement is key to the strength and stability of any retaining wall.
As the soil pushes against the wall, it will want to slide away and/or fall over. The footer supports the wall by providing a solid foundation while the steel rebar inside it keeps the concrete from collapsing and supports the top of the wall. This footing needs to be wide enough so it counters the force against it to prevent rotation/movement. While the added gravel and soil on top of it will further prevent movement. See illustration below:
Good drainage is an essential component of any successful retaining wall
You can have the strongest retaining wall in the world; but without adequate drainage, failure is inevitable. Over time, water can ruin just about anything. We waterproof the back of the wall with roller-grade HLM 5000and then cap it with dimple board (MiraDRAIN 6200). For a retaining wall, we would typically install weep-holes to have a controlled place for excess water to go. But for a hillside foundation wall you wouldn’t want water draining inside the building. So instead, water is funneled down into two 4″ schedule-40 PVC drain-lines and tied into the property’s existing drainage system. Keeping water flowing away from a structure will help to prevent damage and erosion, and ensure its long-term success.
As is typical for most of our concrete projects, the garage floor was poured 5″ thick using fiber-reinforced Class C (city grade) concrete. This is the same product they use for public transportation projects such as streets and sidewalks; and is designed to last a long time. To learn more about our concrete projects click here.
Are you dreaming of a little hillside/addition/garage or grotto? Contact us with your designs, we would love to take a look to see if we can assist you.