MJ Rooney - London’s Specialist Underpinning Contractor
What is Underpinning? Why is it done? How much does it cost? A guide to finding the perfect contractor.
Why MJ Rooney should be your Underpinning Contractor
MJ Rooney is one of London and Kent’s oldest underpinning contractors that have completed many thousands of underpinning projects over the last 35 years. Here are 15 reasons to consider MJ Rooney to be your Underpinning Contractor.
- Family Run Business.
- 10 Years Insurance Backed Guarantees on all Works.
- Trading for 35 Years.
- Highly Trained Workforce.
- Members of the Association of Specialist Underpinners.
- 3D Modeling Sequencing on Every Project.
- Ground Engineering Contractor of the Year Award Winners.
- Highly Experienced Engineers are in the House.
- All Scheduling, Technical Drawings and Surveying in House.
- Building Movement Monitoring Specialists.
- Underpinning Design Specialists.
- Deep Underpinning Specialists below 10m.
- Specialist Underpinning Insurance during Works.
- Professional Design Insurance on all Works.
- Basement Conversion Specialists.
- Specialists in Basement Waterproofing.
What is underpinning? Underpinning Meaning.
Underpinning is the process of increasing the depth of existing foundations. This will help to transfer loads to a lower level.
There are 3 main methods to underpin a building:
- Traditional mass concrete underpinning
- Reinforced concrete underpinning
- Piled underpinning
The traditional mass concrete underpinning has little or no reinforcement. Pouring concrete into the hole forms a block of basement underpinning concrete. This will help to support the house.
The reinforced concrete underpinning is a much thinner wall with lots of reinforcement. It is commonly used in basement constructions.
The piled underpinning method is usually made of circular piles. They are several meters deep to take the wall loads via a ground beam or raft slab.
Underpinning Methods
Underpinning methods can be traditional mass concrete underpinning, piled and reinforced concrete underpinning. We will build individual pins in sequence until they join up to make a single foundation. The video above shows our 3D model displaying the traditional underpinning works. We will use piling to form underpinning in poor ground conditions but this is less common. We will apply basement underpinning to form the walls and foundations of the basement conversion in a single process. This can be the most expensive underpinning method. The reason is that it is likely to have lots more shuttering and reinforcement. Mass concrete underpinning is the cheapest.
When You Should Underpin a House?
You will need to underpin a house if you have one of the following situations:
- if you build a basement conversion
- if you have subsidence
- if you are adding an extra storey to the building
- if you need to dig beside other property’s foundations
Only competent and experienced contractors should do these works. Underpinners need special training and permit systems in place. MJ Rooney’s priority is to guarantee the safety of structures and people.
The process will start with the calculations done by the structural engineer. He will design the best option of the type and the depth of the underpinning. The qualified engineer must also design the temporary works. This will support the building above and keep the operatives safe. The usual length of a single shaft is 1,20 meters. Sometimes deeper pins can be wider by using more structural supports.
Then, the contractor will design the setting out sequence for underpinning excavations. MJ Rooney can draw up a 13524 sequence for your property. This sequence will be marked on-site to help the underpinners to dig in the right order.
Later, the groundworkers will pour concrete within 75mm of the foundation. Then they will allow setting. Finally, they will ram a dry pack mix of sand and cement into the gap. This will support the building without shrinkage.
Basement Conversion
Basement conversion will use reinforced concrete underpinning. This will form the structure in short sections. Each pin section will be fully connected with steel reinforcement. They will all form a complete concrete box. Next, we will underpin the walls to form the completed Basement conversion shell. We will then excavate the central area and install the drainage. Structural waterproofing or tanking will make the structure impermeable. Finally, the basement structure is complete and ready for fitting out.
Underpinning Subsidence Repair
The main reason to use Underpinning Subsidence Repair is to stop foundation movement. This causes cracks to house walls and doors and windows to stick. Your household insurance will normally cover the Repairs once they have determined the causes. The following causes are most likely:
- Soil shrinkage is caused by tree roots desiccating the soil in the summer months.
- Leaking drains washing soil away.
Replacing or lining the drains will help to stabilize the house. You will need to pollard or cut down the trees to reverse the soil shrinkage and avoid the need to do underpinning. You will track crack movements with electronic calipers over time. This will help to discover the cause of cracking. The movement will stop if drain repairs and tree pollarding are successful.
Soil investigation will show if the soil type and the type and depth of tree roots are shrinkable clay. The Underpinning Subsidence Repair needs to be lower than the deepest tree roots.
How much does Underpinning Cost
Underpinning costs can vary considerably but as a rule of thumb, you could consider around £1,000 per m2. There are so many variables to underpinning cost. Any guide price could be inaccurate, and a quotation should be sought. The cost will depend on the following.
Preliminary Costs:
- Engineering design fees including temporary works.
- Party Wall Surveyor fees.
- Skip permits and parking bay suspension.
- Ground testing for contamination.
- Conveyors, Gantry over the pavement.
- Council fees.
- Confined space fees.
Underpinning Cost variables
- Depth – deeper underpinning will be more expensive.
- Chosen Underpinning methods (mass concrete underpinning is cheapest).
- Distance to move the excavated soil.
- Earthwork support design.
- Reinforcement requirements.
- Confined space procedures.
- Reinstatement costs.
- Groundwater and pumping.
Basement Construction Safety
Basement construction safety is essential to every project and MJ Rooney is a specialist in the field with over 35 years of experience. The key safety considerations when underpinning a house are as follows:
- Structural engineering design including temporary works.
- Investigation for underground services.
- Barriers and safe access to underpinning shafts.
- Confined space entry procedures
- Temporary works supervision procedures
