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Building a house extension is an exciting way to create more space without moving to a new property. But once the drawings are approved and the work begins, there are many practical details to sort out. One of the most important is the concrete.
Concrete is commonly needed for foundations, footings, floors, bases, and other parts of an extension. The quality of the concrete matters, but so does getting the right amount to the site at the right time.
For homeowners in London, ready mix concrete can make this part of the building process considerably easier. Instead of mixing large quantities on site, professionally prepared concrete can be delivered when the construction team is ready to use it.
But how much do you need? Which mix is suitable? When should you order it? And what should you consider if your property has restricted access?
Here is what homeowners should know before arranging concrete for a house extension.
Why Concrete Is Important in a House Extension
A house extension needs a solid and properly prepared base. The foundation transfers the weight of the new structure into the ground, while the concrete floor and other concrete elements provide strength and stability where required by the design.
This means concrete is not something that should be selected simply by looking for the cheapest available option.
The appropriate specification depends on the design of the extension, ground conditions, structural requirements, and the instructions provided by your engineer or building professional.
For a homeowner, the easiest approach is to have the project requirements clearly defined before ordering. If your builder or structural engineer has specified a particular concrete strength or mix, give those details to your concrete supplier.
That simple step can help prevent confusion later.
What Is Ready Mix Concrete?
Ready mix concrete is professionally prepared concrete that is delivered to your construction site ready for use.
Traditional site mixing usually involves bringing cement, aggregates, water, and other materials to the property and combining them on site. For a larger pour, this can take considerable time and requires enough room to store the materials.
Ready mix concrete removes much of that preparation from the building site.
The concrete is prepared for the required application and transported to the project location. Once it arrives, the construction team can concentrate on placing, compacting, levelling, and finishing the concrete.
This can be particularly useful for house extensions where the available working area is limited.
How Much Concrete Does a House Extension Need?
There is no standard amount of concrete required for every extension.
A small rear extension may need a very different quantity from a large side extension or two-storey project.
The amount will depend on things such as:
- Length and width of the extension
- Foundation dimensions
- Depth of the concrete
- Floor area
- Slab thickness
- Footing requirements
- Ground conditions
- Structural design
- Additional concrete work
For a basic rectangular slab, volume can be estimated by multiplying length × width × depth.
For example, if an area is 5 metres long, 4 metres wide, and the concrete depth is 0.1 metres:
5 × 4 × 0.1 = 2 cubic metres
That is only a simple example. Real extension projects can include foundations, trenches, uneven areas, and different sections that need separate calculations.
If you are unsure about the quantity, it is better to discuss the measurements with your builder and concrete supplier rather than making an assumption.
Why Ordering the Correct Quantity Matters
Concrete is delivered as a fresh construction material, so ordering the right amount is important.
If you order too little, the team may run out before completing the pour. That can create a difficult situation when workers, equipment, and other trades are already on site.
Ordering too much can also be wasteful.
The goal is to have enough concrete to complete the planned work without creating unnecessary excess.
Before confirming an order, make sure the measurements are based on the actual construction drawings or the information provided by your builder. If the shape of the extension is irregular, break the area into simpler sections when calculating the volume.
Your supplier may also be able to help you understand the quantity required based on the information you provide.
When Should You Order Concrete for an Extension?
Concrete delivery should be planned around the construction schedule.
You do not want the concrete arriving before the site is ready. At the same time, you do not want workers waiting around because the delivery has not been arranged.
Before booking, check that:
- Excavation or groundwork is complete
- Formwork is ready where required
- Reinforcement has been installed if specified
- The pouring area is accessible
- Workers are available
- Necessary equipment is ready
- The weather has been considered
- The delivery time works with the building schedule
Communication between the builder and concrete supplier is important here.
Your builder knows when the site will be ready, while the supplier needs enough information to arrange the appropriate concrete and delivery.
London Properties Can Present Access Challenges
One of the things that can make concrete delivery more complicated in London is the variety of property layouts.
Some homes have wide driveways and plenty of space around them. Others are located on narrow residential streets, behind terraces, or in areas where parking and vehicle access are restricted.
Before booking a delivery, consider how the concrete vehicle will reach the property.
Think about:
- Width of the entrance
- Narrow roads
- Parked vehicles
- Gates
- Low branches
- Overhead obstacles
- Distance from the road to the pour
- Available space for the delivery vehicle
Do not wait until delivery day to discover that the vehicle cannot get close enough to the property.
Tell your supplier about access conditions when requesting a quote. If the site is difficult to reach, they can discuss possible delivery or pumping arrangements with you.
When Is Concrete Pumping Useful?
Sometimes the problem is not getting the concrete to the property. The challenge is getting it from the delivery vehicle to the exact place where it is needed.
This is where concrete pumping can be useful.
A concrete pump moves fresh concrete through a pipeline or hose to the required location. This can be helpful when the pour is behind a building, over an obstacle, inside a restricted area, or otherwise difficult to reach directly with the mixer.
For a house extension, pumping may be worth considering when:
- The rear garden is difficult to access
- The extension is far from the road
- There is a wall or other obstruction
- The property has restricted access
- The concrete needs to reach a specific area
- Manual movement would require excessive labour
The type of pump required depends on the project and site conditions. Metro Ready Mix provides concrete pumping options, including boom and line pump solutions, for projects where access and placement are challenging.
Ready Mix Concrete vs Mixing It Yourself
For very small jobs, mixing concrete on site may seem straightforward.
But an extension foundation or floor can require a significant volume. Mixing that amount manually can become a time-consuming job.
There are several things to consider.
Labour
Someone has to measure and mix the materials throughout the process. This can require additional workers.
Consistency
Producing repeated batches manually requires careful measurement and mixing. Maintaining consistency can be more difficult as the volume increases.
Time
Large quantities can take much longer to prepare compared with having ready mix concrete delivered to the property.
Storage
You need space for cement, aggregates, water, and equipment.
For larger extension projects, ready mix concrete can therefore offer a more practical solution.
Choosing Concrete for Your Extension Foundation
The foundation is one of the most important parts of an extension, so the concrete specification should not be guessed.
Your structural engineer, architect, or builder may provide specific requirements based on the design and ground conditions.
These requirements can include the required strength class, exposure considerations, aggregate size, or other specifications.
When speaking to a supplier, provide the specification rather than simply saying that you need “strong concrete.”
That gives the supplier useful information and reduces the chance of ordering the wrong product.
If you have received a specification from your engineer, keep it available when requesting your quote.
What About Concrete for Extension Floors?
Concrete can also be used as part of the floor construction of an extension.
The required thickness and specification will depend on the overall floor design and construction method.
Your builder may need to consider insulation, damp proofing, reinforcement, screed, floor finishes, and other elements around the concrete.
This is another reason why homeowners should avoid choosing a concrete specification independently when it forms part of a structural or regulated building element.
Use the project drawings and professional specifications as your starting point.
How to Prepare Your Property Before Delivery
Good preparation can make concrete delivery much easier.
Clear the route the vehicle or pumping equipment will need to use. Remove unnecessary obstacles and make sure the work area is ready before the concrete arrives.
If vehicles need to enter a driveway or private area, check that the surface and access route are suitable for the delivery arrangements.
The builder should also make sure the actual pouring area is prepared.
There is little benefit in arranging a perfectly timed concrete delivery if the site is not ready to receive it.
Why Delivery Timing Matters During a Concrete Pour
Once concrete arrives, the construction team needs to work efficiently.
A concrete pour is not simply a matter of tipping the material onto the ground and leaving it there. The concrete needs to be placed and finished appropriately for the application.
If delivery is poorly coordinated, workers may have to wait while other parts of the site are prepared.
That is why it helps to discuss the expected delivery window with your supplier and builder beforehand.
For larger jobs, the timing may need even more careful planning because the pour could involve multiple loads.
Questions to Ask a Ready Mix Concrete Supplier
Before placing your order, ask a few straightforward questions.
What concrete specification do I need?
Provide the specification from your engineer or builder so the supplier can confirm the correct product.
How much concrete should I order?
Give accurate dimensions and ask for help if the project is irregular.
Can you deliver to my postcode?
Confirm the delivery area before making arrangements.
Will the delivery vehicle be suitable for my property?
Discuss narrow entrances, restricted access, and other obstacles.
Do you provide concrete pumping?
If the pour cannot be reached easily, ask about pump hire and suitable options.
What information do you need from me?
Having the required details ready can speed up the quotation and booking process.
Why Use a Local Concrete Supplier in London?
Working with a supplier that understands London delivery requirements can be useful, particularly when your property has access restrictions.
Metro Ready Mix provides ready mixed concrete, volumetric concrete, concrete delivery, and concrete pumping services for residential and commercial projects across London.
The company works with homeowners, builders, contractors, developers, and groundwork professionals. Its service areas include locations such as Uxbridge, Brentford, Barnes, Alperton, Acton, and Twickenham.
The focus is not only on supplying concrete but also on helping customers arrange a practical delivery solution around their project requirements.
What Information Should You Have Ready for a Quote?
When contacting Metro Ready Mix, having a few details ready can make the conversation much easier.
You may be asked about:
- Your project location
- Type of project
- Concrete application
- Approximate quantity
- Required concrete specification
- Preferred delivery date
- Site access
- Pumping requirements
- Number of loads, if known
You do not need to know everything before making an enquiry. If you are unsure about the quantity or delivery method, explain the project and ask for guidance.
A Practical Example: Planning a Rear Extension
Imagine you are adding a rear extension to a London home.
The builder has completed the excavation and prepared the foundation area. The next step is to arrange the concrete.
Rather than simply ordering a random quantity, you would first check the drawings and confirm the required foundation dimensions and concrete specification.
You would then measure the required areas and estimate the volume.
Next comes access.
If the mixer can reach the required area, standard delivery may be enough. If the extension is located at the back of the property and there is no suitable vehicle access, concrete pumping might be the better option.
Finally, the delivery needs to be scheduled for a time when the site, workforce, and equipment are ready.
That is the basic process. It does not need to be complicated when the right information is prepared in advance.
Frequently Asked Questions
Is ready mix concrete suitable for house extensions?
Yes. Ready mix concrete can be used for various parts of an extension, including foundations, slabs, floors, and other applications, provided the concrete specification is appropriate for the project.
How do I know what concrete mix my extension needs?
The required specification should come from your structural engineer, architect, or building professional. Share those requirements with your concrete supplier before ordering.
Can ready mix concrete be delivered to residential properties in London?
Yes. Ready mix concrete delivery can be arranged for residential construction projects, subject to the supplier’s delivery area and site access requirements.
Can concrete be pumped into a rear extension?
Yes, concrete pumping can be useful when the extension is difficult to reach directly from the delivery vehicle. The appropriate pump depends on the layout and access conditions of the property.
How do I calculate concrete for an extension?
For simple rectangular sections, multiply length by width by depth to calculate the volume. More complicated foundation layouts may require separate calculations for each section.
Should I order extra concrete?
It is important to order enough concrete to complete the planned work, but the amount of additional material should be determined carefully. Excess concrete can create unnecessary waste, while too little can interrupt the pour.
Does Metro Ready Mix provide concrete pumping in London?
Yes. Metro Ready Mix offers concrete pump hire, including boom and line pump options, for projects where concrete needs to be placed in difficult-access areas.
Final Thoughts
Concrete may only be one part of a house extension, but getting it right can have a major impact on the construction process.
Start with the project specification, calculate the required quantity carefully, and think about access before arranging delivery. If the concrete needs to travel a long distance from the road to the extension, ask whether pumping would make the job easier.
Most importantly, coordinate the delivery with the people actually working on the project. When the site is ready and the concrete arrives at the right time, the entire process becomes much more straightforward.
For homeowners, builders, and contractors looking for ready mix concrete in London, Metro Ready Mix provides concrete supply, delivery, volumetric concrete, and pumping solutions for a range of residential and commercial projects.
If you are preparing for a house extension and are unsure about the amount of concrete, delivery arrangements, or pumping requirements, contact Metro Ready Mix with your project details and discuss the best option for your site.
