Underpinning is the reinforcement of a foundation that is already in place. It is necessary in the event that the foundation itself isn’t sufficient to support the structure. This usually happens as a consequence 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 building)?
Underpinning is the act of strengthening or supporting the base of an old home or other similar structure. It is done by strengthening the foundation of the building, enhancing the soil by adding an expanding filler or expanding the foundation to ensure it is spread across a larger area.
Why is it necessary to underpin?
For the majority of homeowners needing to strengthen their foundation, the foundation that was built originally isn’t sufficient to support the home. This usually happens as due to:
the soil beneath 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 were not fully understood in the initial design of the foundation. This means the foundation was not designed to the soil conditions.
In less typical cases the need for underpinning may be necessary in the following circumstances:
The way in which the structure is utilized changes e.g. after a major remodel
New construction is happening nearby, which results by the excavating of the soil to support 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, such as floods, earthquakes, or droughts, have caused structures to shift or become unstable.
To determine if and the need for underpinning Let’s take a close review of the main factors that affect the foundation.
Site Classifications and Types of Soils
Soil type is an important aspect in the foundation’s stability. Certain types of soil are susceptible to more substantial structural changes that occur in environment (e.g. when there is prolonged periods of wet and dry conditions) and can cause foundational issues. These soils are referred to as “reactive”.
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The soil type under your home will affect the severity of the damage to your house and the method of underpinning that is best can be used to stabilize the structure.
Class A
“Acceptable” 0-10mm mostly rock and sand sites with minimal or no ground movement due to the moisture changes expected.
Class S
“Satisfactory” 10-20mm A little reactive clay site. Very little ground movement due to water changes is anticipated.
Class M/M-D
“Moderate” 20-40mm moderately reactive silt or clay sites, which may have moderate movement of the ground due to water changes.
Class H1/H1-D
“Highly reactive” 40-60mm highly reacting clay sites. The ground can move a lot caused by changes in the moisture.
Class H2 or H2-D
“Highly reactive” 60-75mm highly active clays. It is possible to experience extreme ground motion due to moisture fluctuations.
Class E/E-D
“Extreme” 75mm+ Highly responsive sites. The ground can move dramatically caused by changes in the moisture.
Class P
“Problem” Sites that contain soft soils, like silt or soft clay, or loose sand, with varying levels of soil filling, land slips miners subsistences, collapsed and collapsing soils the soils that are susceptible to erosion, reacting sites that are subject to unusual conditions of moisture, or sites that cannot be classified in any other way.
“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 encountered in dry areas.
Different types of foundations for buildings and foundations
Technically speaking”foundation” refers to”foundation” is the term used to describe “foundation” can be described as the ground or strata, on that the “footings” for a structure 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 slabs on the ground like the raft slab, waffle pod slab and slabs featuring dropped beams, or the strengthened slab on fill.
Suspended Floors
They are usually covered with piers or stumps they are supported with joists and bearers.
The common footing systems in residential construction comprise of:
Continuous footings
For example, slabs or concrete strips designed to support uniformly dispersed loads.
Pad feet
Like the round or square concrete pad designed to support a large load. It is most often used in conjunction with stumps.
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 the need for additional support is present. This includes poured concrete piers bored pilings driven piles (timber steel, concrete, and steel) along with screws made of steel.
The majority of underpinnings are performed using “Slab on Ground” type foundations.
What is the reason foundations fail to build?
There are a variety of 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. The movement can be caused by shrinkage (which causes the settlement) as well as expansion (which can cause the soil to expand). If the conditions are dry soils slowly lose moisture and begin to shrink. If the moisture levels are high like during prolonged times of rainy weather soils can expand by hundreds of percent.
The expansion and shrinkage of soil may affect the strength that the foundation has, resulting subsidence, heaving, and visible cracks in walls and foundations.
Poorly Compressed Fill
If a location was filled with filler often, the filler material was not compact enough to be able to support the construction’s weight over it. In these instances foundation issues are common. 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 until foundations can be structurally compromised. Erosion can come from various causes, including an uncontrolled water pipe that bursts or any other water flow that is not controlled and drainage problems or similar.
Slope Failure
The failure of a slope is related to the earth’s movement downhill. It can be caused by slow failure, also known as “creep” or sudden failure, both of which can be described as “landslides”. When a slope fails because of creep, underpinning could be employed to correct the issue. But, this is particular to the site and requires a thorough assessment.
Transpiration (aka Trees)
Trees play an important role in foundation collapse. The plants all remove water from the soil. This is called transpiration. Large trees that remove moisture from soil can dramatically accelerate the shrinkage of soil. When trees are situated close to buildings they can cause the expansion or shrinkage of soils to the point that it compromises 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 properties not being fully comprehended during the initial plan of foundation, this means the foundation isn’t sufficient for the terrain. But, with the advent of the modern building codes, this becomes not as important.
Different types of underpinning
In the earlier part of the article, underpinning is strengthening foundations already in place.
When it comes to fixing the foundations of buildings that have stumps, the procedure employed is known as restumping or Reblocking. It is basically replacing stumps of the foundation when they have been damaged or cracked. This isn’t 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
There have been historically two major underpinning techniques employed. This is 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 grouting or injection.
Concrete slab
Historically concrete underpinning was used to boost the foundation’s size and to make them stronger. It’s still being used frequently in the present.
Screw pile
It is a popular 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 considered to be a permanent solution – one that is not affected by any 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 underpinning. It involves injecting grout or resin into the ground , which creates voids underneath the slab. The slab expands and then making the ground more compact. It’s the most difficult to quantify method in terms of the 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 isn’t suitable for all soil conditions.
Do I need underpinning?
There are some indicators to be aware of when conducting an independent assessment of your home. In reading this list, it’s essential to know that subsidence can occur on many properties at different levels. The need for underpinning only occurs when subsidence is taking place. When subsidence occurs, it is possible that it is when the structure has reached an equilibrium state which means there’s no risk. If you aren’t sure you are not sure, seek out an expert.
Cracks in floors and walls
Cracks don’t need to be frightening. Sometimes, they’re just superficial and minor, like hairline cracks in the plaster, cornices as well as skirting boards. Cracks that are more extensive and typically indicate bigger root causes, like uneven weight distribution caused by weak foundations.
The cracks you should look for could be either interior (plaster tiles, floor and wall tiles) or external (brickwork or concrete slab, render).
Try to look at the cracks over the course of time. This can be done over a period of weeks or even months. find out if the cracks appear to get larger in size, width or length or if new cracks begin to appear. If they aren’t changed over a prolonged period then the subsidence may have taken place 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 you notice a slight lean towards one or the other sides of your home is a sure sign that there are serious foundation issues to be considered.
In the most serious cases we’ve seen it is possible to stand at the end of a hallway and observe the house fall down when you walk 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 degree of unevenness in a room. Place a ball inside an area and observe whether it stays in place or moves in a certain direction. However, to comprehend how important this is , it’s best to consult an expert.
Another thing to be aware of is the formation of irregular trenches 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 are excellent indicators of foundation problems. There are gaps appearing and growing 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 it is possible to see more the door’s leans windows or doors, and the door frames could begin to separate from the wall they are surrounded by.
How do I get help?
None of these indicators can guarantee that you’ll require underpinning. However the last thing you want to just sit around waiting until your symptoms start to become serious. If you’ve done a self inspection of your house, there are concerns then the best thing to do is to remain relaxed – there’s plenty of support readily available.
