# 10.3: Activity 10B - Can a House Contribute to Slope Failure?

It is commonly believed that building a house (or some other building) at the top of a slope will add a lot of extra weight to the slope, which could contribute to slope failure.

What does a house actually weigh? A typical 150 m2 (1,600 ft2) wood-frame house with a basement and a concrete foundation weighs about 145 metric tonnes (319,670 pounds). However, most houses are built on foundations excavated into the ground, which involves digging a hole and removing material, so to accurately determine weight we’d need to subtract the excavated material weight. Let’s do that now.

The foundation dug for our example house requires an excavation 15 m by 11 m by 1 m deep.

1. Calculate the volume of “dirt” removed. Hint: Volume = L x W x H. Show your work.

Volume of “dirt” removed =

1. Our “dirt” typically has a density of about 1.6 tonnes per cubic metre (t/m3). Calculate the weight of the soil that was removed. Hint: Mass = Density x Volume. Show your work.

Weight of “dirt” removed =

1. Which weighs more: the dirt removed to build the foundation, or the house and its foundation?
2. What can you conclude from this comparison?
3. How might a building (house or other) change the drainage on a slope?