HOW TO UNDERPIN A HOUSE FOUNDATION
UNDERSTANDING THE HOUSE UNDERPINNING PROCESS
Once a structural surveyor or engineer has confirmed that your house foundations need to be underpinned possibly after a prolonged period of monitoring he or she will be able to tell you more about the type of underpinning that is best for your particular situation.
For most techniques, the underpinning process generally involves these stages:
STAGE 1: EXCAVATION
First, the ground around the foundations is dug out, either to create cavities into which concrete is then poured, or so that the contractors can insert reinforcing beams or piles.
STAGE 2: PREPARATION
If the mass pour method is to be used, which involves pouring concrete into a hole under and/or around your existing foundations, formwork is then put in place, and reinforcing steel wires set up. This is essentially a mould that ensures the new concrete mass is the correct size and shape and in exactly the right location.
STAGE 3: REINFORCEMENT
In mass pour underpins, concrete is now poured into the form and allowed to set. If piles are being used, they are driven into the ground or fitted to bore holes that have already been drilled out, until they are anchored on a stable layer of soil.
The underpinning process is always started from a corner and then followed inwards along the load-bearing wall being underpinned.
STAGE 4: INFILLING
Most of the soil that had been excavated in Stage 1 is backfilled and compacted.
STAGE 5: REPAIRING THE BUILDING
Once your foundations have been stabilised to prevent further movement of the structure they support, work can finally begin inside and outside your home to repair cracks and redecorate. This may include fixing damage to paths, your drive, patio and garden walls or fences. Homeprotect buildings insurance covers you for these costs when they are a result of the same cause that damaged your home.
As soon as the experts start to draw up plans for underpinning your house, don’t forget to ask whether you need to move out of the property, and how long you are likely to need to vacate it for. This will enable you to plan whether you simply need to arrange to stay with friends or family for a couple of days, book a week in a nearby hotel or B&B, or find a holiday let where you can live for several weeks.
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Your Questions Answered
Underpinning is the strengthening and stabilising of the foundations of a house.
Unfortunately for homeowners faced with the prospect, there is no such thing as a standard cost for underpinning a house because the works involved are unique to the property, the reasons for underpinning, and the underpinning process used. A structural surveyor will be able to give you an approximate idea of the cost. Of course, if the problem is covered by your home buildings insurance, the cost of underpinning a house shouldn’t be something you need to worry about.
The main reasons for underpinning are that the structure of a property has become unstable. In turn, this happens when the foundations can no longer adequately support the building because:
- Its usage has changed, for example, because an extension has added which puts extra strain on the foundations of the main building.
- The wrong type of foundation was chosen when the property was designed arising from mis-classification of the soil type.
- The structure of the soil in which the foundations sit has changed, usually because of too much or too little water in it, causing subsidence.
Underpinning a foundation is a construction or renovation technique to strengthen the base on which a house sits. There are numerous foundation underpinning techniques available for underpinning foundation works. These involve either strengthening the soil surrounding the foundation or reinforcing the foundations themselves.