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Underpinning

Underpinning is a reliable way of supporting the foundation of homes built on shifting soils.

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From shifting soil and improper drainage to renovations and poor compaction during construction, many factors can weaken a foundation. The damage will occur over a long time and if the foundation is not stabilized, it will start to settle and sink. The good news is that underpinning offers a way out of this problem. Read on to learn everything you need to know about underpinning. 

What Is Underpinning? 

Underpinning refers to the process of strengthening existing foundations. It often involves laying additional support below the ground level. The foundation is extended either in breadth and/or depth to distribute the weight of the house over a larger surface area or provide more support. 

The process starts with excavating the soil underneath the foundation. Work takes place in stages to minimize the risk of structural damage. An engineer will assess the soil and determine the appropriate depth of the foundation. The underpinning solution is installed, and the process is repeated until the problematic foundation is strong and stable. 

When Should You Use Underpinning? 

Underpinning is necessary when the original foundation becomes too weak to support the weight of the house. This is usually due to: 

  • Changes in the soil around the foundation as a result of erosion, large trees nearby, expansion and contraction due to moisture, subsidence, or damaged plumbing left unrepaired 
  • Failure to consider soil characteristics properly during the initial design phase 
  • Changes in how the structure is used especially after a renovation 
  • Natural disasters like earthquakes and droughts that move or destabilize the structure 

Are You a Candidate for Underpinning? 

While a professional assessment is always best, the following foundation problem signs should prompt you to take action. 

Cracks in floors and walls: Some cracks are superficial but bigger ones are usually indicative of an underlying issue like uneven weight distribution due to a weak foundation. Look for cracks in the walls, floor tiles, plaster, concrete slab, render, and brickwork. 

Doors and windows out of alignment: If you find it hard to open or close your doors or windows, or notice gaps around them that get wider, consult a professional. In more advanced cases, a door will lean, and the frame will pull away from the walls. 

Uneven, sagging floor: This isn’t always as obvious a sign as cracks in the walls. However, a floor leaning to one or more sides could be an indication of a serious foundation problem. 

Temporary Underpinning Solutions 

There are various types of underpinning solutions available, and the kind used to repair your home depends on the type of foundation you have, its condition, and the extent of damage. Some methods are only temporary solutions, like the ones below. 

Mass Concrete Underpinning 

Mass concrete underpinning involves replacing the soil under the foundation and pouring concrete. Soil is contained and placed in a predetermined sequence so as not to compromise the bearing capacity of the foundation. While this may offer some respite to foundational issues, it won’t prevent the foundation from shifting. 

Pile and Beam Method 

A mini-pile is installed on either side of the foundation walls and the brickwork below the wall is removed. The piles are then connected, and the wall is supported using a reinforced concrete needle. This method is suitable when you need to increase the load capacity of the foundation, or there is restricted access. It is faster than traditional underpinning and offers less disruption, but lots of consideration goes into its design and implementation especially with regards to corrosion resistance and structural compatibility. 

Piled Raft 

This method will come in handy if the entire structure needs underpinning. It works when the soil is too hard for small equipment to excavate, or the foundation is too deep for ordinary underpinning methods. Piles are placed at predetermined locations and pockets below the footing are broken. Reinforcing beams are then placed and linked with a ring beam before concrete is poured. On the downside, internal floors have to be removed completely before the solution is applied. 

The Best Underpinning Solutions 

While temporary solutions can get you by, it’s the permanent underpinning solutions that will have a lasting impact on your foundation. We strongly recommend these solutions: 

Helical piers: Similar to giant screws, helical piers are usually driven down to the bedrock. They are useful in supporting lighter structures like porches and chimneys. 

Push piers: Crafted from galvanized steel, push piers can help raise the foundation back to its original level and stabilize it. 

Slab piers: These systems are widely used to strengthen and can help lift back sinking slab foundations. 

Start Protecting Your Foundation 

Be sure to request a free foundation inspection and repair quote from the professionals at Tar Heel Basement Systems. Our experts will assess your foundation and recommend the right underpinning solution for you.