Soil Grading and Surface Drainage

by | Apr 8, 2022

A soil grading and surface drainage survey or inspection is also commonly referred to as surface slope and drainage. The slope of the lot will greatly influence the surface water flow. If you live on a sloped lot, the surface water will be pulled gravitationally downhill. If one side of the lot surrounding your home is sloped toward the foundation, surface water will flow toward the structure. It is also prudent to take into account the type of soil the home rests upon. If the soil drains well, much of the surface water will drain through the soil and down into the water table. If you have poor draining soil, such as clay-rich soil, the surface water will not drain well and could intrude into the soils below your foundation and structure as a whole. 

Supersaturation of Soil in a Soil Grading and Surface Drainage Survey

Supersaturation of soil is a problem. Supersaturated soil is not stable and if the exterior temperatures dip below the freezing point, the water in the soils could freeze, expand and allow “heaving” to occur. Heaving is what happens to soils when they shift upwards. This happens in one of two ways: Seismic activity or freezing. If there is a long freeze while the exterior surfaces are wet, there is an opportunity for the soils to shift or heave and the result could negatively affect the foundation, and in turn, allow the structure to shift.


Soil Grading and Surface Drainage

Adding Surface Drainage After a Surface Drainage Survey

If soil drainage is a problem where you live, or if the slope of the lot your home was built on allows water to flow toward your structure, surface drainage would be an added benefit. Surface drains could be added to a lot in the form of spot drainage, a French drain or a berm. 

  1. Spot drains could be installed in an area where you already notice water tends to accumulate. This will normally be a low spot in the soil surface, but it could also be a location where a lot of surface water is directed via downspouts, should they terminate above ground.
  2.  A French drain is a drain system that is installed in a trench and placed strategically to collect surface water that flows toward the structure. The type of drainpipe used in this option has slits or holes in the pipe that allow water in so it can flow unobstructed to the termination point of your choosing, further away from the structure. 
  3. A berm could be built on the surface of the lot. A berm is a small mound made of locally sourced soil that is built up in a straight line to guide the surface water flow in another direction. You will want to use local soils from your lot or an adjacent area that has the same composition as the soil on your lot. The reason for this is to make sure the added soils atop the original soils can meld together and create a solid surface that is difficult for water to penetrate and therefore will flow around this built-up surface rather than through it.

Surface drainage is an important portion of the health of the home and the enjoyment of your property. Just because the current slope or drainage situation isn’t the best-case scenario, doesn’t mean you cannot make some additions and upgrades to engineer it the way it needs to be. These efforts are a permanent installation. They will require some maintenance over the years to keep the surface drains clear of organic debris or make sure the berms are holding and not being affected by soil erosion. As long as the moisture has a clear path to drain through, and the drain always has an uninterrupted slope to the termination point, these drainage installations will increase the value of your home as well as the comfort of using your property in whatever manner you like all year long.

Soil Grading & Surface Drainage Survey with Octopus Home Inspections

If you’re in the Portland Metro area (Oregon) and looking for a quality home inspector, schedule a home inspection with Octopus Home Inspections. Octopus Home Inspections is committed to upholding a strong code of ethics, including professionalism and integrity. Our home inspections are extremely thorough, fairly priced, detailed, and accurate. We provide each client with a comprehensive written report, document our observations with numerous color photographs, and offer unlimited follow-up support to ensure any and all concerns you may have are addressed. We look forward to hearing from you.

“It was an absolute joy to work with Chris. He did two inspections for us and his attention to detail was unlike anything I’ve ever seen. My husband and I are first-time home buyers and we are so grateful that he was part of our home buying experience. Both reports were received within 24 hours and left us feeling significantly more informed and prepared to make important decisions. I am genuinely excited to direct friends and family to him for inspections in the future.” – Sydney (5 Star Google Review)