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Types of underpinning

Underpinning is the reinforcement of the foundations of buildings. It is necessary to strengthen the foundation when it isn’t sufficient to support the building. It is typically the result of a change in the soil’s structure, either because of the type of soil or an external force on the soil. Check out the following article for more in-depth details.

What is the foundation (of the structure)?

Underpinning is the act of helping or strengthening the structure of a foundation, home or other structure. This is done by strengthening the foundation that is already in place, by strengthening 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.

Why is it necessary to underpin?

In the majority of homes needing to strengthen their foundation, the foundation of the house is not 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 design process of the foundation, which 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 overhaul

New construction in the area results from the digging of soil that supports foundations that are already in place

to increase the strength of foundations that are 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 determine if and the need for underpinning we will take a closer look at the most important components that influence the foundation.

Site Classifications and Soil Types

It is the soil’s type that plays an important aspect in the foundation’s stability. Certain types of soil are susceptible to more substantial structural changes in condition of the soil (e.g. in prolonged periods of dry and dry conditions) and can cause foundation issues that are structural. We refer to these soils as “reactive”.

The type of soil under your home can affect the severity 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 sites and sand, with minimal or no ground movement due to 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 be subject to moderate ground movement due to the changes in moisture.
Class H1/H1-D

“Highly reactive” 40-60mm highly reacting clay sites. They can experience significant ground movement due to changes in moisture.
Class H2 or H2-D

“Highly reactive” 60-75mm highly active clays. They can experience extremely high ground movement due to changes in moisture.
Class E/E-D

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

“Problem” Sites that contain soft soils like silt, soft clay or loose sand, with varying levels of soil filling, land slips mining subsistence and collapsing soils the soils that are susceptible to erosion, sensitive sites subject to extreme conditions of moisture or that are not classified as such.

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

Foundations for building types and foundations

Technically speaking”foundation” is the term used to describe”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 often 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 a variety of slab on the ground like an raft slab, a waffle pod slab and slabs featuring dropped beams, or an solid slab that is filled with fill.

Suspended Floors

They are usually constructed using piers or stumps they are supported with joists and bearers.

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

Continuous footings

Like an concrete slab or strip designed to support uniformly dispersed loads.

Pad feet

For example, the round or square concrete pad designed to support a heavy load. Commonly used with stumps.


Made of hollow steel, timber poles or posts.

Piles and Piers

Similar to stumps, but made of wood and drilled in the earth. Typically, they are used when more support is needed. Included are concrete poured piers, bored pilings driven piles (timber steel, concrete) along with screws made of steel.

The majority of underpinnings are done using “Slab on Ground” type foundations.

What is the reason foundations fail to build?

There are many reasons the foundations of a structure could fail.

Reactive Soils

The most common cause of concern is due to the moving of soils that are highly reactive. This can cause shrinkage (which results in settle) as well as expansion (which results in the soil to heave). If the conditions are dry soils lose water slowly and begin to shrink. When the levels of moisture are high for extended periods of rainy weather, soils can expand up to several hundred percent.

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

Poorly Compressed Fill

If a place was filled with filler often, the filler material isn’t compact enough to hold the construction’s weight over it. In these instances foundation problems are often the result. The issue could stem from poor compacted fill, use of several filling materials, or both.

Site Erosion

Erosion is a process that can wear away the foundations’ soil to the point that foundations can be structurally compromised. Erosion can be caused by many factors, like the burst of a water pipe, any other water flow that is not controlled or drainage issues or other similar causes.

Slope Failure

Failure of a slope can be attributed to the motion of the earth downhill. It can be caused by the slow breakdown, commonly referred to as “creep” or sudden failure, both of which is known as “landslides”. When a slope fails because of creep, underpinning could be utilized to fix the issue. However, this is local to the area and requires a thorough assessment.

Transpiration (aka Trees)

Trees play a major role in foundation collapse. The plants all remove water from the soil. This is called transpiration. Large trees that remove water from soils can dramatically accelerate the shrinkage of soil. If trees are placed close to buildings it can result in the expansion or shrinkage 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 could be due to soil’s characteristics not being properly recognized during the initial conception of the foundation, which means that the foundation was not suitable for the soil conditions. However, thanks to contemporary building codes, this becomes less of a problem.

The types of underpinning

In the earlier part of the article, the term “underpinning” refers to the reinforcement of the foundation already in place.

In the case of repairing the foundations of structures with stumps, the technique employed is known as restumping or Reblocking. It is basically replacing stumps of the foundation when they have been damaged or cracked. It is not considered to be underpinning.

Underpinning is a term that refers to the process of putting it in place There are three different methods that are currently in use:

Concrete slab

Screw pile

Injection of resin or grout

In the past, there have been two primary underpinning methods employed. This is slab-underpinning in concrete (also called slab jacking) and screw pile underpinning (also called the pier underpinning method (also known as piering). Recently, a third technique is being employed, which is known as grout , or resin injection.

Concrete slab

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

Screw pile

This is a typical method that combines concrete footings and steel piers to support the structure and ensure that the lift is returned to its place of origin, closing cracks and gaps. Piers are thought to be a permanent solution, one that is not affected by any changes to the ground around the home – that’s the reason we choose this method.

Grout / Resin injection

This is the most recent method of underpinning, but it’s not underpinning. It involves injecting grout or resin into the ground , which creates voids underneath the slab. It then expands, making the ground more compact. It’s the most difficult to quantify method in terms of the durability of repairs and price at the end (the quantity of grout needed isn’t easily calculated and often exceeds the initial estimates) and is not suitable for all soil conditions.

Do I need underpinning?

There are some indicators to look out for when performing an independent assessment of your home. In reading this list, it’s crucial to realize that subsidence can occur on many properties at different levels. The need for underpinning only occurs when subsidence is occurring. In some cases, after subsidence first occurs it is when the structure has reached equilibrium which means there’s no risk. Always, if you aren’t sure then seek out 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 issues that are underlying, like uneven weight distribution because of weak foundations.

Cracks to look out for can be in the interior (plaster wall and floor tiles) or external (brickwork and concrete slab, render).

Try to look at the cracks over the course of time, either weeks or months, to find out if the cracks you’ve observed get deeper in size, width or length or if new cracks begin to appear. If they don’t change over a prolonged period then the subsidence may have taken place and the house is now been able to settle.

Floor is not equal

A problem that’s not always as apparent as cracks is uneven floors. If you can detect them, however you notice a slight lean towards one or more sides of your house is a clear indication that there are serious foundation issues to be considered.

In some serious instances we’ve witnessed it is possible to stand at the end of a hall and observe the house fall down as you gaze down the hallway. Sometimes, floors that aren’t level could cause misaligned doors. It is common to utilize a spirit-level to determine the degree of unevenness in a room. Place a ball inside the room to see whether it stays stationary or rolls in a specific direction. To understand the significance this is , it’s best to consult an expert.

Another thing to watch out for are the irregularly-shaped trenches that form around the edges of the slab or building within the top layer of soil. Another sign of subsidence.

Windows and doors that are out of alignment

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

In more severe cases there may be more obvious the door’s leans windows and doors. Door frames could begin to separate from the wall they are surrounded by.

What is the best time to seek help from underpinning contractors Toronto?

None of the indicators above do not guarantee that you’ll require underpinning. However the last thing you want to be waiting around 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 plenty of support to be found.