- By spizspy
- In Underpinning Cost
Which Underpinning Method Should I Choose?
Excavation
If your foundation is no longer adequately supporting your home, it may be time to consider underpinning. Traditionally, concrete underpinning has been the go-to solution, designed to strengthen and expand existing foundations. While still widely used, an alternative method—expanding resin injection—has emerged as an effective option in many cases. Though only qualified underpinning professionals should handle this job, having some background knowledge of the available methods will help you make a well-informed decision when seeking quotes.
Why Is Underpinning Necessary?
There are several reasons why a foundation may lose its ability to support a structure effectively:
- The original foundation may have been built incorrectly.
- Soil subsidence can cause foundations to sink over time.
- Excavations near your property may weaken your foundation.
- Additional weight, such as adding a second storey, may require the foundation to be strengthened.
- Natural disasters like flooding or earthquakes can weaken or shift the foundation.
Understanding why underpinning is needed can provide valuable insight into selecting the right method. For instance, if your foundation was improperly constructed or you’re adding a second storey, soil subsidence may not be the issue, and concrete reinforcement could be the best approach. On the other hand, if nearby excavations or soil movement are causing problems, a different type of concrete reinforcement or even resin injection may be the better option. After conducting a soil test through a geotechnical engineer, a structural engineer can guide you in selecting the appropriate underpinning method.
Concrete vs. Resin Injection Underpinning
Several underpinning methods are available, but they generally follow the same principle: concrete underpinning increases the foundation’s mass to make it stronger. Concrete underpinning usually involves substantial excavation around or under the existing foundation.
There are two primary types of concrete underpinning:
- Mass Underpinning: This method involves digging around and under the foundation, then pouring concrete to increase the foundation’s mass.
- Concrete Pilings: These are essentially concrete “nails” driven deep into the ground, with the foundation attached to the piles for added reinforcement.
Resin injection, on the other hand, is a more streamlined process often used in areas with reactive soils. Little to no excavation is required, as the resin is injected through small holes drilled into the ground around the foundation. As the resin is injected, it fills the voids in the soil, binds with it, and expands as it dries, stabilizing the soil and making it less reactive.
If your property is located near the beach or in sandy areas, another method called soil grouting may be recommended. This process is similar to resin injection, but instead of resin, a polymer grout is injected to bind sandy or granular soils, creating a more stable base for your foundation.
Deciding Between Concrete and Resin Injection
Concrete underpinning can be a slow and labor-intensive process, requiring significant excavation. However, it can be a cost-effective solution for smaller jobs and, depending on the specifics of your property, may be the only viable option.
Resin injection, while faster, can vary in cost depending on how much resin is required. Since it’s difficult to predict how much resin will be needed—especially in soil with fissures—this method can sometimes end up costing as much as concrete underpinning.
Regardless of the method you choose, the key is ensuring that the solution is long-lasting and that future underpinning will not be needed. When comparing quotes from contractors, it’s important to look at not just the price, but also the product and workmanship guarantees. A job done by a reputable professional with strong guarantees is always a better investment than simply choosing the lowest price.