When to repair the foundation of a historic Portland home
There’s no question that old homes in Portland have character. But while charm and rich history rule the view from above, many of these homes face a challenge below ground. Hundreds of historic Portland homes today sit on crumbling, compromised, or poorly constructed foundations. If you own a Portland home built before the 1960s, you might already be considering when the right time may be to repair your foundation.
Looking for answers to your home’s foundation woes? You’ve come to the right place. At Lamont Bros., our team loves the challenge of working on older homes. In fact, a few of our team members own historic homes, themselves. We know how stressful it can be to wonder if your home’s foundation is structurally sound.
In this article, you can read about why and how to repair a compromised foundation in an old home. Once you’re finished reading, you should be able to identify action steps you can take to get your foundation on the road to recovery. This article will discuss:
What are some common foundation problems in historic Portland homes?
Most of the historic homes in Portland were built before the Uniform Building Code was published in 1927. As a result, many building practices of the age followed a set of loose guidelines rather than tested and proven construction codes.
Time has shown that many methods used during the housing booms of the early 20th century were not adequate for building safety or structural integrity. As a result, most historic homes in Portland require some form of repair to remain a safe living environment.
For some of these homes, the greatest challenge is a faulty foundation. During the early 20th century when these homes were built, there was no set way to pour a foundation. As a result, most builders did their best with what limited understanding they had of structural concrete. Since then, these old foundations have shown to possess several potentially hazardous defects. To reduce the structural risks of these historic Portland homes, the foundation may require some repair.
Earth-Formed Poured Slab
In the late 1800s and early 1900s, the method for pouring a foundation was much different than it is today. Back then, home construction began by excavating the home’s footprint, usually by hand or with the help of a work animal. Once the home site had been dug out, workers would pour concrete directly into the hole until the concrete reached the level of the ground.
This type of foundation where the hole in the ground is used to shape the foundation is called an earth-formed poured foundation. The issue with this method is that an earth-formed foundation does not have a spread footing, which distributes the weight of the structure evenly into the soil below. A spread footing is like a snowshoe – by spreading the weight of the load above over a larger area, the structure can hold more weight.
Because an earth-formed foundation does not have a spread footing, the structural integrity of the home is held by skin friction. This is the bond between the foundation walls and the dirt around them. The problem is that the foundation must remain undisturbed to maintain this skin friction. This makes it very difficult to excavate around the foundation for waterproofing or any structural assessments.
When these historic homes were constructed, the foundation slab usually reached ground level. At the time, homebuilders knew that a home’s floor should be elevated above ground level. But instead of using concrete foundation walls to elevate the structure as we do in homes today, they build cripple walls.
A cripple wall is a timber-framed wall that elevates the home’s floor above the foundation. Because they were made of wood, cripple walls tend to be more susceptible to rot and structural failure. In addition, these cripple walls are not designed for lateral rigidity, which means resistance to bending. This makes cripple walls especially susceptible to damage during a seismic event. They do not provide adequate structural protection to the rest of the home, and the damage could be catastrophic if not addressed in time.
Weak Concrete Mixture
Another source of potential hazard is a bad concrete mixture. Portland saw a massive housing boom in the early 1900s. Unfortunately, homebuilders had not yet gotten concrete mixing down to an exact science. During the boom, high demand for concrete meant low supply. To work with what little supply they had, some unscrupulous builders diluted their mixtures with sand and gravel.
The result was a weaker concrete mixture that became extremely brittle once it dried. After over 100 years, most of those foundations made with bad mixtures are ready to fully retire. Some have eroded, cracked, or simply crumbled away.
How can I repair my Portland home’s compromised foundation?
Clearly, old homes can pose several challenges when it comes to foundation integrity. Fortunately, modern construction technology has yielded several options to remedy these issues. Below are some of the most popular ways to repair an old foundation and ensure the structure’s continued safety.
This is one of the most common types of foundation repair jobs for Portland homes, and with good reason. Nobody wants their house falling down during an earthquake, and a seismic retrofit helps prevent that.
Most projects in this category follow a prescriptive process laid out by building code requirements. This process often involves timber blocking to re-distribute structural load, as well as adding sheathing to the foundation. These alterations act to provide a type of shear wall within the foundation, which prevents collapse in the event of an earthquake.
A typical seismic retrofit for a Portland home costs between $7,000 – $10,000. For a project like this, it’s best to get a permit for the work so that the building records show the home has been updated for seismic protection.
Auxiliary foundation walls
In the case that the structure of a foundation wall is compromised, the best solution is to reinforce it. There are two primary methods of reinforcing a compromised foundation wall.
The first option is to install a shotcrete wall. Shotcrete is a pneumatically expelled concrete with high-tensile strength. When constructing a shotcrete wall, the first step is to create a steel framing to support the shotcrete. Once the frame is in place, the shotcrete gets hosed onto the frame to create a new vertical wall.
The second option is to construct a new strip footing and foundation wall directly next to the existing foundation wall. The downside to this option is that the new wall takes up space in the home’s basement. However, it is a much less expensive option than the shotcrete wall.
Total foundation replacement
If seismic retrofit or reinforcement won’t work to solve your foundation woes, you could replace your foundation. Due to the complexity and cost of a project like this, a total foundation replacement should only be considered as a last resort.
In order to replace a foundation, the first step is to sever the home from the old foundation. After that, you’ll have to put the home on a temporary support structure, demolish the old foundation, and then build a new one in its place. This type of foundation repair is one of the most technically challenging because it requires a lot of excavation and engineering.
Still, if your old foundation is beyond saving due to the poor building practices of days gone by, this can be the way to go. Keep in mind that a full foundation replacement can cost over $300,000. On the bright side, it is an opportunity to remake your basement exactly as you want it. With the astronomical cost of replacing your foundation, finishing the basement into a usable living space can often be worth the trouble.
Want to talk to the pros about your crumbling foundation?
Now that you have some ideas on how to repair your historic Portland home’s foundation, are you ready to take on the challenge? If so, keep learning about the remodeling process! Check out our Guide to Remodeling In Portland Historic Districts, where you can learn about the regulations that preserve our historic Portland neighborhoods.
When you’re ready to start designing your basement remodel, click the button below to schedule a free video design consultation. Our team of professional designers will help guide you through the process of remodeling your home from start to finish.