Before a beautiful new home starts to take shape above ground, there is the slightly more mucky task of preparing the site with underground foundations and drainage. This is known as groundworks.
Each site is unique and has its own individual requirements when it comes to working in the ground. Tricky access or sloping ground are common characteristics that don’t have to be project threatening but need careful thought.
As a potentially complicated and risky part of a project, choosing a turnkey company (like Facit Homes) that does absolutely everything, including groundworks, is an intelligent choice.
For many of our customers, we replace an existing dwelling. So, the first step before the groundworks is to demolish that building.
Building new is often a more practical option for those considering refurbishment, extensions or relocation. Mostly because it provides our customers with exactly the home that they want to live in.
The demolition of residential properties is generally straightforward and costs around £8,000 - £20,000 for a single property. The actual cost and time it takes depends on the size and complexity of the demolition - for example, a suburban site will likely need a lot more time and care as there are neighbouring properties to protect.
It can save on other costs too. Existing service connections to electricity, mains water and sewage can usually be reused, and access to the road can be maintained - as opposed to developing a greenfield plot (although of course, there would be no cost for demolition).
Investigating the site
Before groundworks can be planned, we take great care to investigate the site, work through the options and carry out our due diligence to ensure that stable foundations can be created. Our 3D model and digital designs help us to provide early solutions to site issues such as steep slopes.
Step 1. We work with a specialist surveyor to conduct a thorough geotechnical investigation which involves creating boreholes and testing the soil to show the physical makeup of the ground. This might also involve carrying out tree root investigations to determine the impact of any roots on the foundations.
Step 2. Based on this information we determine what we believe will be the optimum foundation design and most practical solution for the site, for example a raft foundation, piles or strip footings.
Step 3. Our structural engineers then provide an interpretative report of the investigation results and confirm our foundation solution or propose any changes based on their analysis.
When deciding the best foundations for a site, we usually choose a product based system as they fit best with our digital approach and can be designed and manufactured to our exact requirements.
It’s about choosing simplicity when you need it most.
Groundworks with Facit Homes
As part of our turnkey service, we take care of the complicated details whilst putting our customers in control of decision making. Turnkey is inspired by ‘turning the key’ and means that we provide our customers with a ready-to-use product, taking care of the project from design and planning to demolition, groundworks and construction.
We do also take on construction-only projects, so whether we’re building our own design or that of another architect, we take great pride in providing intelligent construction and strong foundations as part of that.
Groundworks at Vermas
For our latest project, a unique family home in Barnet, the first step was to demolish the existing 1970s home. Before they found us, our customers had researched renovating and extending their home in an attempt to improve the spaces and reduce the energy bills.
Instead, they found they could design and build their dream home with us in a more cost-effective way - with less compromise.
In order to demolish their draughty existing property, our customers moved into a temporary home and we disconnected the site from the utilities i.e. gas, electricity and water.
Demolition took 4 weeks from start to finish and, once the existing home was gone and the site had been cleared, we graded the footprint of the house to correct the level. Grading the footprint of the home involves flattening the area of the building (measured by the outer edges) to the right height. The site was also cleared of all other materials, such as the driveway surface and other hard landscaping.
Once the building area was levelled and ready for construction work to begin, we started to excavate trenches in order to create strip footing foundations for the house.
Strip foundations (or strip footings) are a type of shallow foundation that are used to provide a continuous strip of support to a linear structure, such as a wall built centrally above them.
Resolving the steepness of the driveway
One of the biggest site challenges for this project was the steep driveway. By bringing one side of the driveway down to the street level we created better access for the new house, and a flatter surface for cars to be parked on. The other side of the driveway was closed off by retaining walls that raised the level up to create a proper front garden outside the new front door.
This meant a large and complex groundworks package with lots of changes to the levels of the site and the installation of essential retaining walls to mould the site into a more practical design.
Our 3D digital model for this stage detailed retaining walls in order to support the different ground levels. After excavating the driveway, we built the retaining walls into the landscape and backfilled the site to create the two distinct levels.
Backfilling is the process of reusing the soil removed during the excavation work to build up the correct levels of the site behind the retaining structures.
To retain the earth in the landscape outside the footprint of the building, the retaining walls were built using a Stepoc system. This involves hollow Stepoc concrete blocks engineered to fit together before concrete is poured into the gaps from above.
Next, we installed underground drainage. This system of pipes and fittings is installed below ground level to transport foul drainage and rainwater away from the building.
Following this, we reconnected the utilities to a new external meter box on site. Once this was complete, we could start to install the beam and block foundations.
A raised, insulated beam and block is one of two solutions that we use at Facit Homes.
The area has clay soil, which meant the most appropriate foundation system was a combination of beam and block and concrete strip footings. Clay soil is subject to something known as 'heave' where the clay soil swells and shrinks as it absorbs and releases moisture. Tree roots exacerbate the issue, even if the tree has been felled. Generally, this means we need to create a gap between the ground and the slab.
This site was slightly complicated because parts of the strip footings needed to also act as the retaining walls for the newly lowered driveway.
Beam and block foundations are quick to install. The resulting labour savings make it cost-effective, too, despite the slightly higher cost of the materials.
The other benefits are improved acoustic performance, higher thermal mass and greater fire resistance. What’s more, the beams and blocks are inert material so they are unaffected by damp, rot or vermin.
The underfloor heating system was laid on top of the beam and block foundations and pressure tested to ensure there were no leaks. Concrete was then poured on top to create a slab that keeps the heating pipes in position.
The concrete slab is heated up by the underfloor pipes, which in turn warms the floor. This approach avoids inconsistent patches in underfloor warmth. To finish off the groundworks, we power floated the concrete slab to create an even surface.
This approach uses the minimum amount of concrete possible for the slab. Including the underfloor heating zone it is just 100mm thick so it is very efficient.
For more information about how we can help you build your home, please contact the studio on 020 3034 7020 or email firstname.lastname@example.org