Lot Grading & Final Grade Tips

Why are rough & final grade so important?

Water is essential to life, but it can also be one of the most destructive forces nature can throw at us. Rough & Final grades exists to help prevent water damage in buildings.

Water damage in a residential building generally occurs in several ways, one of which is overground flooding

Lot grading addresses overground flooding. It is the engineering and implementation of elevations, slopes, and swales, to manage surface water by directing it to a controlled drainage system.

Rough Grade & Final Grade Explained

The rough grade is the of shaping the ground (clay, in Edmonton) to prepare for the final grade. Important points on the lot are marked with survey stakes. The rough grade survey is done to ensure the lot meets the City's drainage plan.

The final grade complements the rough grade by finishing with topsoil or ground cover. This must also be done to meet key survey points on the lot. If the final grade conforms with the lot grading plan the result is that all surface water will freely flow away from the building to a controlled drainage system.

Final Grading Tips

Slope away from the house

It is important to remember that a minimum 10% slope is usually required within the first 2 meters of the building. This translates into at least 8" away from  the building within the first 6'6". This slope helps deal with the inevitability that your back-fill will settle.

The basement of your home was probably made by digging a deep hole in the clay, and then pouring concrete foundation. After the concrete cures, loose clay back-fills the void surrounding it. So if the final grade requirements for slope away from the house seems a bit drastic, think of how you be glad of it when the back-fill starts to settle.

NOTE: Don't forget about those tough to reach areas like under then deck. We have seen many well executed final grades fail because the slope under the deck was not adequate.

Continuous slope

The final grade stakes are generally placed when the rough grade survey is completed. It is important to make sure these remain undisturbed so the final grade can be accurately matched to the marks on them.

While it is critical that the height of the soil is within tolerance of the marked final grade, it is also important to remember the principle of continuous slope:

• Except in the case of a mid-yard high point, the swale on the property line should slope continuously without changing direction.

The overaching principle here is that if your yard is designed to drain from front to back, you have to make sure that there are no low spots where water can pool (even if your grade matches the lines on the final grade stakes).

One of the common tricks to ensure your slope is continuous is by using a string line. A string line can be stretched taught between two grade stakes. Provided there is no sag in the line,  you can use it as a guide to ensure your slope stays continuous. It is very easy to see low or high spots when you have the string line as a reference.

Free-draining ground cover

If you choose to complete your landscaping before getting your final grade surveyed, it is important to consider what constitutes free-draining. The final grade survey will verify the ground height, ignoring free draining material.

This means that if you are putting decorative rock on your side yard, and you have to come up 4" to meet your final grade, you must install 4" of topsoil or clay and then put your rock on top. The reason for this is that rock is free-draining, ie: water will not run on top of it, but it will fall through. If the surface below is too low you will end up with pooling, settling, and potentially water damage issues.

Happy Grading!