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Do I need underpinning?

Underpinning is the reinforcement of a foundation that is already in place. It is necessary to strengthen the foundation when it isn’t sufficient to support the structure. This usually happens as a result of a change in the soil’s structure, either because of the type of soil or any external force on the soil. Find out more details.

What is the foundation (of the structure)?

Underpinning refers to the process of strengthening or supporting the base of an old home or other structure. This is done by strengthening the foundation of the building, enhancing the soil through the introduction of an expanding filler, or by extending the foundation to ensure that load can be spread across a larger area.

What is the best time to use underpinning?

In the majority of homes needing to strengthen their foundation, the foundation that was built originally isn’t sufficient to support the structure. It is typically due to:

the soil that supports the foundation has been altered in the way that supports the foundation e.g. through subsidence, expansion/contraction due to moisture, large trees nearby, damaged plumbing left unrepaired.

the soil’s characteristics weren’t fully understood in the initial design of the foundation. This means the foundation was not designed to the soil conditions.

In less frequent instances it is necessary to underpin in the following circumstances:

The method by which the structure is utilized is changing e.g. after a major remodel

New construction is happening nearby, which results by the excavating of the soil to support foundations

to increase the strength of foundations already in place e.g. for supporting a second storey of the structure

Natural disasters like flooding, earthquakes or droughts caused the structure to shift or become unstable.

To better understand the need for underpinning Let’s take a close review of the main components that influence the foundation.

Click here for the best underpinning contractors Toronto.

Site Classifications and Soil Types

Soil type is an important aspect in the foundation’s stability. Certain types of soil are susceptible to more severe structural changes in condition of the soil (e.g. in prolonged periods of dry or dry climate) and, consequently, contribute to foundation issues that are structural. We refer to these soils as “reactive”.

The type of soil that you’ve got beneath your home can affect the degree of the damage to your house and the best method for underpinning can be used to stabilize the structure.

Class A

“Acceptable” between 0 and 10mm, mostly rock and sand sites with minimal or no ground movement because of the moisture changes expected.
Class S

“Satisfactory” 10-20mm A little reactive clay site. There is only a slight movement of the ground due to water changes is to be expected.
Class M/M-D

“Moderate” 20-40mm moderately reactive silt or clay sites, which may have moderate movement of the ground due to the changes in moisture.
Class H1 / H1D

“Highly reactive” 40-60mm highly reacting clay sites. The ground can move a lot due to changes in moisture.
Class H2 or H2-D

“Highly reactive” 60-75mm highly reacting clay sites. It is possible to experience extreme ground motion due to moisture fluctuations.
Class E/E-D

“Extreme” 75mm+ Highly sensitive sites. They can experience extreme ground movement due to changes in moisture.
Class P

“Problem” Sites that include soft soils like silt, soft clay or loose sand. They can also include varying in depth of the fill mining subsistence and collapsing soils sandy soils susceptible to erosion sensitive sites subject to extreme conditions of moisture, or sites that are not classified as such.

“D “D” included in these classifications is referring to the ‘deep’ movement of soil caused by deep variations in the amount of moisture. These classifications are typically located in dry regions.

Different types of foundations for buildings and foundations

Technically speaking”foundation” refers to”foundation” is the term used to describe “foundation” refers to the ground or strata on that the “footings” to support a building are built. But the term “foundation” is frequently used to mean”the “footing system” as well as”flooring systems” or the “flooring system” which together form the foundation.

Slab on Ground

There are many kinds of slab on the ground including the raft slab, waffle pod slab or slab featuring dropped beams, or an solid slab that is filled with fill.

Suspended Floors

The foundations are typically constructed using piers or stumps which are supported by joists and bearers.

The common footing systems in residential construction are made up of:

Continuous footings

Like slabs or concrete strips that is used to support evenly weights that are evenly distributed.

Pad feet

Like an oval or square concrete pad designed to support a large load. It is most often used in conjunction with stumps.


Made of hollow steel, timber poles, or machined timber posts.

Piles and Piers

Like stumps, however they are they are driven or bored through the soil. Commonly , more support is needed. This includes poured concrete piers bored pilings driven piles (timber steel, concrete) as well as screws made of steel.

Most often, underpinning is done in conjunction with “Slab on Ground” type foundations.

What is the reason foundations fail to build?

There are a variety of reasons the foundations of a building may fail.

Reactive Soils

The majority of the time, the issue is related to the moving of soils that are highly reactive. The movement can be caused by shrinkage (which causes the settlement) as well as expansion (which results in the soil to heave). If the conditions are dry soils slowly lose moisture and begin to shrink. If the moisture levels are high for extended times of rainy weather soils can expand up to several hundred percent.

The expansion and shrinkage of soil could weaken the structural integrity that the foundation has, leading to rising, subsidence and visible cracks in walls and foundations.

Poorly Compressed Fill

If a location was filled with filler it is possible that the fill was not compact enough to be able to support the load of the structure that is over it. In these situations foundation problems are often the result. The cause could be poor compacted fill, application of multiple filling materials, or both.

Site Erosion

Erosion is a process that can wear away the foundations’ soil to the point that foundations are structurally damaged. Erosion can come from various causes, including the burst of a water pipe, any other water flow that is not controlled or drainage issues or other similar causes.

Slope Failure

The failure of a slope is related to the motion of the earth downhill. It can be caused by slow failure, also known as “creep” or sudden failures, which can be described as “landslides”. If a slope is failing because of creep, underpinning could be utilized to fix the issue. But, this is local to the area and requires an assessment by a professional.

Transpiration (aka Trees)

Trees play an important role in foundation collapse. Every plant removes moisture from soil. This is called transpiration. Large trees that drain moisture from soil could significantly speed up soil shrinkage. When trees are situated close to buildings they can cause the shrinking or expansion of soils that could compromise the foundation.

Foundation Design

In a lesser extent it is possible that the initial design of the foundation could have been insufficient. This may be due to the soil’s characteristics not being properly comprehended during the initial plan of foundation, which means that the foundation was not suitable for the soil conditions. But, with the advent of contemporary construction codes, this is not as important.

Different types of underpinning

As we discussed earlier in the article, underpinning is the reinforcement of the foundation already in place.

When it comes to fixing the foundations of buildings that have stumps, the technique used is called restumping or Reblocking. This is basically replacing the stumps of the foundation when they have been damaged or cracked. This isn’t considered to be underpinning.

In this definition of underpinning there are three ways that are currently in use:

Concrete slab

Screw pile

Resin injection or grout

There have been historically two major underpinning techniques that have been used. They are slab-underpinning in concrete (also called slab jacking) and screw pile underpinning (also called Pier underpinning (also known as piering). Recently, a third technique is being utilized, namely grout , or resin injection.

Concrete slab

Historically concrete underpinning was used to boost the foundation’s size and, in turn, consolidate them. It’s still being used often nowadays.

Screw pile

This is a typical method, that involves combining concrete footings and steel piers to ensure the structure is secure and lifts are returned to their initial position, thereby closing cracks and gaps. Piers are thought to be a permanent solution, one that won’t be changed by changes to the ground around the building – this is the reason we choose this method.

Grout / Resin injection

It is the most advanced method of underpinning, but it’s not really underpinning. It involves injecting grout or resin into the ground , which fills in the voids beneath the slab. It then expands, making the ground more compact. It’s the most difficult to quantify method in terms of durability of the repair as well as the price at the end (the size of the grout needed isn’t easily calculated and frequently exceeds the initial estimates) and is not suitable for all soil conditions.

Do I need underpinning?

There are a few indicators to be aware of when conducting an independent assessment of your home. In reading this list, it’s crucial to realize that subsidence is a common feature of properties in varying degrees. The need for underpinning only occurs when subsidence is occurring. When subsidence occurs, it is possible that and the structure is in equilibrium which means there’s no risk. If you aren’t sure you are not sure, consult an expert.

Cracks in floors and walls

Cracks don’t have to be scary. Sometimes they’re minor and minor, like hairline cracks in cornices, plaster or skirting boards. More severe cracks can be a different story and often point to larger root causes, like uneven weight distribution because of weak foundations.

The cracks you should look for could be in the interior (plaster tiles, floor and wall tiles) or external (brickwork and concrete slab, or render).

It is recommended to examine the cracks over a time of time. This can be done over a period of weeks or even months. examine if the cracks that you’ve observed get deeper and longer, or wider or if new cracks begin to appear. If they aren’t changed over a prolonged period it is likely that the subsidence has been completed and the house is now become settled.

Floor isn’t equal

A problem that’s not always so obvious as cracks are uneven floors. If you are able to spot them the presence of a lean on one or more sides of your house is a clear indication that there are serious foundation issues to be considered.

In the most serious cases we’ve seen it is possible to sit at one end of a hall and observe the house fall down as you gaze down the hallway. Sometimes, floors that aren’t level can cause doors to be misaligned. It is common to make use of a spirit level to gauge the level of a room. You can also place a ball into the room to see whether it stays stationary or rolls in a specific direction. However, to comprehend how important this can be, you’ll need the expertise of a professional.

Another thing to watch out for is the formation of irregular trenches around the edges of the slab or building or slabs, within the top layers of soil. Another sign of subsidence.

Doors and windows that are not in alignment

Windows and doors can be an indicator of foundation issues. The gaps are appearing and becoming larger around your doors and windows. You are finding it difficult to shut (or open) your windows or doors or to secure them.

In more severe cases it is possible to see more doors that are leaning towards them windows or doors, and the door frames could begin to separate from the walls around them.

What is the best time to seek help?

None of the indicators above can guarantee that you’ll require underpinning. However it is important to not just sit around waiting until symptoms get serious. If, after completing a DIY evaluation of your home, you are concerned then the best thing to do is to remain relaxed – there’s lots of assistance readily available.

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