The Underpinning under existing foundations of existing house.
Reinforcement and concrete installed down to the depth of 2.5 meters, dry packed and floor lowered to put in new concrete slab in Manchester.
The Underpinning of existing foundations, down to the depth of 1.2 meters and bricked up onto underpin to tie back onto the wall.
Crack stitching rebar carried out in Watford.
Why choose to underpin?
There are many reasons why your home may need to be underpinned. Protection against subsidence is the most common, but you may choose to underpin your home for other reasons.
For example, you might want to add an extra storey to the building, in which case the foundations may not be strong enough for the extra weight. Or you may choose to create a basement, which will require new foundations further down.
There are four main reasons why underpinning may be necessary
The original foundations are simply not strong enough anymore. Older buildings weren’t always designed to today’s standard and their foundations may no longer be adequate.The use of the existing structure has changed. If you are building an extension or adding another floor, you need to take into account the extra strain it will put on the original foundations.
The structure of the soil, in which the foundations sit, has changed. This can be caused by a particularly thirsty tree soaking up all the water underneath your property or by a leaking drain that is softening the ground, washing the soil away and causing the foundations to shift.
Either way, when the subsoil is drawn away from the foundations, it can create a cavity, which the building will slowly drop into, causing subsidence.
Repeated flooding.
Mass Concrete Underpinning
Also known as traditional underpinning, this is the oldest method still in use. It involves excavating sections below the foundations, one at a time, and backfilling each with concrete before moving on to the next.
Mass concrete underpinning is slow and very labour intensive, which often makes an alternative method preferable. However, its biggest advantage is that it involves no heavy machinery, which can often make it preferable in situations where access to machinery would be difficult.
Reinforced Concrete Underpinning
Basement walls need to support the vertical loads from the existing structure and resist the horizontal forces from the ground, hydro-static pressure and from any other surcharge loads such as the foundations of nearby structures or vehicles on roads.
Multi-stage underpinning
Multi-stage underpinning can be used to build deep reinforced concrete walls either as part of a deep single level basement or when constructing multi-level basements.
Multi-stage underpins allow shallower individual underpin excavations which can be advantageous from a health and safety point of view, especially in unstable soils.
Beam and Base Underpinning
The beam and base method of underpinning also involves excavating, as with traditional underpinning. In this case, however, instead of concreting the whole space, mass concrete bases are placed in strategic positions.
A concrete beam is then laid across the bases. This takes the weight of the building above it and transfers the thrust further down to levels of subsoil that are more robust than those closer to the surface.
Do you need an expert assessment?
If you have any uncertainty, why not book in a Home Checkup with one of our experts. Or if you just want to pick our brains a bit, then pick up the phone to us now. We will be more than happy to help.