Home Building Process Phase 4 - Excavation & Foundation

Phase 4 is where the excitement begins.  With the lot staked and cleared, the excavation and construction can begin.

Excavation & Foundation Begins

When it comes to building your home, there’s a great deal of work that goes on behind the scenes before you can take the first steps towards constructing the building itself.

One important stage in the process and the very first step when it comes to the process of building is excavation.

If you’re building a new house, then you most likely included an expense like this in your budget. Excavation isn’t always easy, nor is it a particularly inexpensive step in the process, but it’s one that’s vitally important nonetheless –especially in Colorado Springs, where there’s an abundance of soil that’s unsuitable for foundations.

Earlier on in Phase Three, we covered the process of determining the approximate location for your home site. This was based on things like view, driveway, and drainage.

Now, we’ll take a look at excavation –a measure that’s vital for laying the foundation upon which the home will be built. Read on to see what’s involved in this process, and what you should know about cost, timing, and how it all unfolds.

Excavation: The First Step in Creating a Solid Foundation

As you may already know, Colorado is home to what’s known as ‘expansive soils’ –soils that can change volume when they soak up water. The most common types of expansive soils are clays and silts. These soils will draw water in whenever it’s available.

Naturally, this type of soil can pose a real threat to potential homes, as it can compromise and damage the foundation.

While these soil types can be found throughout the states and Canada, they’re especially prevalent in California, Arizona, Nevada, Colorado, and other western and southern states.

There are a tremendous number of structures across the states that have been subjected to damage that’s caused when moisture-absorbed soils expand. In fact, it’s estimated that the annual cost of expansive soil-caused damage in the U.S. is $2.3 billion, according to Benson, Kerrane, Storz & Nelson, P.C. That’s more than twice the damage caused by floods, hurricanes, tornadoes, and earthquakes combined.

When it comes to expansive soils, this underestimated but tremendously destructive force can usually be seen within the first few months, or in some cases, years, after a home is built. As water from the rain or irrigation systems filters through to below the home’s foundation it can cause a condition known as ‘edge-lift.’ This can cause cracking in the foundation and can also be seen as cracks in the home’s walls. Over time, ‘center-lift’ can also occur; which is when moisture reaches the center of the housing slab, resulting in even more extensive damage.

In most cases, excavation is a vital part of ensuring that the ground beneath the home is suitable for a strong foundation.

What Happens: A Brief Overview

When it comes to your home’s design, the attentiveness and diligence that’s taken at the start will have a long-term impact on the structure’s strength and integrity.

Home Builders are required to enlist the services of a geologic engineer, to prepare a soils report on the conditions of the soils at the building site. This report would identify any expansive soils. By doing this, they’ll be able to give recommendations on how to build a home that will be able to mitigate or minimize the effects of expansive soils. Some of the measures that are often taken include the removal of these soils, hauling in new, non-expansive soils, chemical treatments, post-tensioned floor foundations, or even imposing limits on irrigation systems or requiring the installation of drainage systems.

Before Excavation: The Survey

At Homes By Michael Hall; We like to be involved in the process of lot selection. This accomplishes two things; first of all, it enables us to help determine where the ideal building location will be. Additionally, we can be involved with the geological testing at the build site prior to our client’s purchasing. If the site won’t work or the cost of excavation is too high, our clients can terminate the deal during the inspection period of the transaction, minimizing additional expenses.

We start by staking out a rough footprint for the home. We’ll then have a geologic engineer test within the envelope of the site. This testing is required in order to obtain a foundation and footer inspection which are ultimately required for a final building permit.

Since the samples must come from within the actual building envelope, it’s helpful to flag the actual boring holes for the surveyor.

Based on the results of the soils test, we’ll receive one of the following from the geologic engineer:

  • Approval to proceed in the desired site location, or
  • Conditional approval based on bringing the soils at the site up to an acceptable standard

In the case of conditional approval, the general course of action includes what’s known as an ‘over dig and backfill.’ With this approach, the excavator will over dig; beyond the actual size of the foundation. The scope of the over dig will be determined by the geologic engineer. In most cases, they may ask for a four-foot over dig, while less common, there may be a recommendation for the dig to be up to ten feet.

Ultimately the surveyor will finalize the site plan and placement, officially staking the property in order to produce an approved plan.

Excavation Begins

Once we have an approved plan, excavation begins.

A professional excavator will come in and begins digging.

The excavator will use the approved plan and staking report in order to know where to dig.

The depth that they will dig depends on a number of factors, including the type of foundation, whether there will be a crawl space, and whether there will be a basement.

No matter what type of foundation you ultimately choose, it will most likely need to be placed on cement footers. Due to frost mitigation requirements here in the Pikes Peak Region or anywhere the ground freezes for that matter, we actually pour the foundation walls on cement footers that will be placed at least 30” below the surface.

The idea is to keep freezing water away from the footers. As water freezes it expands—this expansion can create and exert enough force and pressure can literally lift and crack these cement footers and ultimately the foundation and house.

The type of foundation will be the deciding factor as to how deep the footers ultimately end up.

Let’s look at each of these foundation types and how they affect excavation and footer depth now:

Slab: This is the most basic of foundation types, as the name suggests it is a simple concrete slab. There is a wide range of options and variables that pertain to the slab foundation, enough for a complete article.

The important point for our purposes is that slab foundations still need to meet frost mitigation requirements. This requirement will generally drive the cost up to the point where it makes more sense to build on a basement or crawlspace.

Crawl Space: A crawl space has become a popular option for our aging population. A crawl space still requires at least 30 inches of excavation, at least along the Front Range in order to protect the foundation from frost. In the mountains, 36 to 40 inches is generally the minimum requirement.

Crawl spaces are often thought to add substantial cost savings when building a home. This is not the case as most of the cost the excavation is actually getting the equipment out to the site and started. Digging an additional 4 to 6 feet doesn’t have that much of an impact on the overall cost.

Basement: This is by far the most popular type of foundation, at least here along the front range of Colorado. The basement provides a great foundation system with the added benefit of extra storage space or affordable finished living space.

There are different types of basements as well; Full basement, Garden Level and Walk out. More on these in another article.

The basement excavation certainly costs more but when you weigh the cost against the other options and frost mitigation requirements, the basement turns out to give home owners the best bang for the buck.

The Open Hole Inspection

At the end of the excavation comes what’s known as the ‘open hole inspection.’ At this stage, the geologic or soils engineer will revisit the site and inspect it to confirm that the soils in the open hole match the sample taken from the drill log and that it meets the recommendation of the soils report.

Once the engineer signs off on the soils and condition of the open hole, we will be ready to start the process of pouring the foundation.

How Long Does It Take?

Excavation for a foundation can range from 3 to 4 days, on up to 3 weeks.

Generally, a worst case scenario will involve a 10-foot over dig. This tends to happen in areas where there are boulders. We have seen these types of excavations in areas like Cedar Heights. This is a beautiful location on the west side of Colorado Springs –and it has stunning views, but building in this area and ones like it often present a significant challenge.

Once the dig is complete, we’ll then have it backfilled with non-expansive, or ‘structural fill soils,’ although in some cases, the engineer will allow the soil to be removed, conditioned (wetted down), compacted, and returned.

How Much Does It Cost?

The cost of excavation itself can vary considerably depending on the contractor that you use, as well as the extent of the job. For instance, excavating a patch of land that’s easily accessible and contains few trees is far cheaper than clearing a remote patch that contains large boulders that are stuck in clay. Generally, though, you can expect to spend between $10,000 to $30,000 on excavation costs in most areas. Be sure to obtain a few different estimates from excavation companies up front. Also, keep in mind that extra excavation, hauling away dirt, disposal fees, and bringing in new soil, can all add to the cost.