Foundation and Drainage Basics | Boise Home Inspector | Dwell Inspect Idaho

Home Foundation and Drainage Basics

A home inspection is an important part of buying a house. For the buyer, an inspection provides valuable information about the condition of the home, and serious foundation and drainage issues can ruin a sale.

The purpose of inspecting the foundation is to determine if the base of the home is structurally sound. Structural issues can lead to sagging roofs, slanted floors, and cracks that leave the home vulnerable to pests and water damage.

Factors That Contribute to Foundation Problems

A home’s foundation can be damaged by environmental changes like earthquakes, extreme temperatures, and tree roots. However, the most common contributing factors are:

1. Soil

Most lots will have some amount of fill dirt, because the majority of the lots that homes are built on aren’t level and need to be properly graded. Low areas need to be built up with fill dirt, and if the slope of the lot isn’t sufficient, retaining walls will be required to hold the fill dirt. This is because the areas that have fill dirt don’t get compacted as well as they should, and that can compress over time leading to settlement.

When foundation soil experiences an extreme change in moisture content, this can result in damage to the foundation in the form of settlement. An excess amount of moisture is capable of saturating the soil of the foundation, which can lead to a softening or weakening of the soil. When the soil is no longer capable of supporting the load, the result is often settlement of the foundation. Different soil types are affected by moisture in different ways.

Foundation Tench | Boise Home Inspector | Dwell Inspect Idaho
Foundation Soil | Boise Home Inspector | Dwell Inspect Idaho
  • Sandy soils. Sandy soils are more predictable, because water passes through rather than being absorbed. Instead of expanding and contracting as they absorb moisture and dry out, respectively, sandy soils are fairly consistent in volume and density. They rarely cause foundation problems because they are less likely to shift and settle, giving them stability and good load-bearing qualities.


  • Clay soils. Soils that are rich in clay and silt have the greatest potential to damage a foundation. Clay easily absorbs water, which causes it to expand in volume as it becomes more saturated. Clay soil causes foundations to crack, heave, and shift. When clay soils dry out, they shrink and crack. This leaves gaps around a house where water can easily penetrate and repeat the expansion cycle. Clay soils typically cause more foundation damage by expanding rather than contracting.


  • Sandy loam soils. Loamy soils tend to be a very stable soil that shows little change with the increase or decrease of moisture. The biggest concern with foundations built on loamy soils is erosion. When soils underneath the foundation erode, they are less able to sustain the weight of a foundation.
2. Home Age

This might seem obvious, but the age of the home affects the foundation as well. Foundation strength relies a lot on the size and amount of beams present. Older foundations tend to have smaller and fewer beams, making them less stable than homes built today. Today’s homes typically have larger and more beams present, adding stability.

3. Poor Drainage

Moisture can be a serious problem for homes in general, but it’s worse when it comes to foundation. Poor drainage will affect the foundation because when water collects around a house, the saturated soil around the foundation expands and shifts. That pressure on the foundation walls increases and results in cracks and leaks that allow water to penetrate the foundation. This is bad for a number of reasons, but it can cause electrical hazards, mold growth, and structural damage. We go in to more detail on drainage further down.

Inspecting the Foundation

When home inspectors get to the foundation portion of the home inspection, they’ll be looking for things like foundation cracks, uneven levels, and damaged walls and floors. If there is a crawlspace under the house, they’ll have to carefully examine it to determine if it’s wet or musty. If there are wet or rotten areas, there may be foundation drainage problem that needs to be corrected.

Small cracks in the concrete (less than the size of a nickel) can be considered normal, but larger and visibly deep cracks are signs of a bigger problem. Your inspector may recommend that a structural engineer come in and do a thorough inspection of the foundation. It’s important to remember that home inspectors can’t diagnose a foundation issue. They can only report on what they saw during the inspection. It’s ultimately up to the home buyer to decide if they want to bring in an expert (or the seller, if they’re having an inspection done before they list the home).

Ultimately what they’re looking for, whether it’s in a basement or a crawlspace, is that there are no large cracks and everything is dry.

Foundation Crack | Boise Home Inspector | Dwell Inspect Idaho

When inspecting the exterior of the home, your inspector will also be looking for drainage issues around the home. If there is standing water right next to the foundation, there may be issues inside as well. Poor drainage can be caused by improper grading, or gutters that are clogged or drain too close to the house, just to name a couple. If there is standing water outside of the home, they’ll want to be sure to take a closer look once inside the home to ensure that the foundation is dry.

Foundation Drainage

A recent study by the Concrete Foundation Association (CFA) shows that 85% of home structural damage is caused by poor drainage. As a homeowner, it is important to deploy preventive measures to avoid greater expenses down the road. Exterior drainage systems offer a timely solution to avert property damage caused by surface water.

To appreciate the reasons to invest in surface drainage outside your home, you need to consider what can go wrong if you don’t. Surface water causes lateral pressure against foundation walls. The consequences include:

  • Foundation cracks which compromise the integrity of the house.
  • Basement leaks leading to flooding and property damage.
  • Health risks caused by mold growth in the basement.
  • Loss of home value due to water damage
  • Damaged landscape

These problems highlight the need for exterior drainage to keep water away from your yard and the foundation walls. Below are some systems that can be installed to solve the problem of poor surface drainage:

Foundation Drainage | Boise Home Inspector | Dwell Inspect Idaho
1. French Drain

This is a perforated pipe that is installed in a flat yard to drain away standing water. It involves excavating a trench that slopes away from the property and the pipe is then installed. A porous material such as gravel is used to fill the trench before the trench is finally covered. Standing water follows the easiest escape route meaning it will seep down to the French tile and drain away from your yard.

2. Footing Drain

This is a highly effective water drainage system. A pipe is installed around the perimeter of the foundation walls on level with the footing. This pipe collects any water that would have leaked through the top of the footing into the basement and drains it away from the foundation walls. The drain is covered with gravel up to the soil’s surface.

3. Gutter Drainage System

Roof water can cause havoc if not well drained. A gutter and downspout system help drain away all roof water away from the house walls. The downspout drain should extend away from the walls and preferably direct the water to a storm sewer or catch basin.

4. Grading Drainage

This is a simple technique that involves reworking the grading in order to slope away from your house. A contractor will assess the gradient needed to drive water into the storm sewer within the building code.

Talk to your contractor today if you notice standing water on your yard. It could be a disaster in waiting in case of flash storms.


Other Signs of a Foundation Issue

  • Small cracks in the exterior walls or stairs are usually nothing to worry about, but larger cracks or cracks that have a zig-zag pattern can be signs of a foundation issue.
  • Doors that are no longer square and have cracks in the wall above them are another sign that there may be a foundation issue. Homes settle over the years, but cracks above doors are usually a sign of more than just a house settling.
  • Uneven floors can also be a dead giveaway of a structural issue. If you can visibly see that the floor is slanted, that’s a red flag. If water spills on the floor or you drop something and it rolls one direction, that’s another bad sign.

Bottom Line

The first step in ensuring you are making a sound investment is to always have a home inspection conducted by a certified inspector. Most of the time you aren’t going to run into any serious foundation issues, but there may be times where you do, so it’s important to understand what to look for and what may be causing it.



Schedule Your Inspection

Use our online scheduling system to book an inspection today or call our office with any questions.  Once you have selected a day and time, your job is done.  Allow our team to handle it from there.

Related Posts