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What Is Underpinning And What Is It For?
Underpinning is the process of strengthening the foundation ground underneath an existing building or structure. Traditionally underpinning involved excavation of the soil underneath the building and replacing it with a stronger material – usually a form of concrete.
There are three reasons why you may need underpinning services, these are:
- For a conversion/extension project
If you’re going to convert the structure above the ground to something heavier such as adding another level/storey to a house, or to something that has another function than the original purpose such as converting a residential building to a commercial or industrial unit, you may need to strengthen the ground below to accommodate to increased load.
- For protection from future issues
If it’s identified that your building is sat on foundations that are neither strong nor stable, or if nearby excavation works would affect the soil that supports your existing structure, you may need to strengthen the ground below to help prevent future issues arising.
- To rectify current issues that the building is facing
This is the most common reason for needing underpinning work completed on your property. Underpinning helps to stabilise the foundations and re-level buildings that have subsided, helping to return them to their previous state. Traditional underpinning would typically take weeks / months, however, Mainmark’s world-leading resin injection solution can complete the task and bring the building back to level in as little as one day.
The fundamentals of underpinning can be found in history books and technical papers dating as far back as the 15th century. Obviously, as the world has progressed, so have the methods of underpinning. Nowadays, underpinning can be completed in as little as one day and without the need for occupants to leave the building, if the right method is selected. Take a look at the different methods available below:
- Mass concrete underpinning
Mass concrete underpinning is a traditional method of underpinning and more than likely the method that most people would think of if someone asked them to describe underpinning. It involves excavating the ground below the building or structure in boxed sections and then filling the excavated ground sections by pouring concrete into it. This solution is carried out from the outside/perimeter of the structure and is traditionally low-cost but only suitable for shallow foundations.
- Piled underpinning
Piled underpinning takes place when the foundation load needs to be transferred to stable soils at deeper depths. Usually, the soil is inadequate to bear the weight of the structure above. Other reasons for piled underpinning include if there are environmental concerns regarding excavated soil, or if there are access issues to the construction site. It is a system used when the whole property has been affected by subsidence and involves the removal of the internal floors so that a grid of steel cased piles can be installed and filled with concrete. The structure can then sit on top of the piles for support.
- Computer-controlled grouting
Computer controlled grouting uses a multitude of injection ports to deliver high-mobility grout into the ground, under precise computer control, to gently raise the structure in a non-invasive way. Each computer can be programmed to control up to 128 injection ports at once, enabling lifting of very large areas or complex heavy structures. The non-invasive injection ports are only 25mm-40mm in diameter and remain in place for the duration of the work. The self-contained grout batching and control centre is housed within a self-contained unit to minimise onsite footprint and is demountable when necessary to enable access to restricted areas of buildings or infrastructure.
- Resin injection underpinning
High tech, advanced engineered resin injection underpinning is an efficient way to rectify subsidence and re-level structures. Using a process likened to keyhole surgery, an expanding polyurethane resin mix is delivered into the ground via an array of small-bore injection tubes (typically 16mm diameter around the perimeter of the building or 6mm if carried out inside). A chemical reaction and consequent expansion occurs as the components mix together, upon entry to the ground. This reaction and expansion strengthens the ground and the building is returned to level in a controlled manner.
Resin injection underpinning is a fast, non-invasive and overall cleaner alternative to traditional concrete or piled underpinning and is suitable for a broad range of buildings and soil types.
There’s no hiding it, traditional concrete and piled underpinning can be very expensive. Methods of underpinning such as mass concrete underpinning or piled underpinning can range from anywhere between £1,500 per m² all the way up to £2,600 per m² according to a report from My Job Quote. There’s also the added cost of accommodation and relocation of the occupants whilst the property has to be vacated.
Mainmark’s resin injection underpinning is a lower cost and more efficient alternative to these traditional methods. Each job is costed by its specific needs so you’re only ever paying for the solution that is right for you. Generally, you could expect resin injection to be around 20% cheaper than concrete underpinning and around 50% cheaper than piled underpinning. Another advantage is that resin injection is completed in 1 – 3 days, compared to alternatives that take between 4 – 6 weeks.
When looking at the cost of underpinning, it’s important to also understand the long-term implications of not having the work done. For example, if you’re having it done to correct subsidence, the longer you leave it, the worse the subsidence will get. You’ll end up paying more to correct subsidence that has deteriorated and in the worst-case scenario, your property could collapse completely if the ground beneath it becomes too unstable.
A property that has suffered from subsidence will often be worth less than one that has had no previous issues. This is due to the risk of further subsidence or issues. The amount that the property will be devalued by will depend on how bad the issues were and how recently they occurred. A 2021 report by SOLD.co.uk found that houses affected by subsidence saw a valuation decrease of 20% – 25%.
When looking at insurance on a house that has suffered from subsidence, there may be a limited number of providers available. If you’ve had subsidence issues that are now rectified, your existing insurer should normally continue to cover you afterwards. Alternatively, you can contact BIBA (British Insurance Brokers’ Association) for a specialist broker. You’ll be wanting to look for an insurer who will ‘transfer’ the insurance to a new buyer. This will make any future house sale much easier as it alleviates one of the issues a potential buyer may face.
Underpinning doesn’t have to be costly, messy or time-consuming. Our friendly team can advise on the best course of action to repair your property’s ground issues and our world-leading resin injection or computer-controlled grouting underpinning methods allow us to fix subsidence in a cost-effective and non-intrusive manner.
Contact our team today, call us on 0800 975 0507