Grand Designs London Basement
MJ Rooney built this basement extension on a tiny site in East London that was featured on Channel 4’s Grand Designs. The Client had what he thought was a basement specialist but with disastrous consequences when the sides began to fall in and concrete shutters burst. MJ Rooney saved the day by repairing the half-built structure and completing to a perfect and waterproof finish.
London Basement Fail
Grand Designs decided to feature the construction of this small basement project located in centre of London due to its remarkable aspirations. Little did they know the story that would unfold.
Building contractors in London can create some of the world’s most spectacular structures. Unfortunately, when the clients employed the project’s first groundworks contractor, they never thought that would be the beginning of the nightmare! And the worst thing is that Grand Designs would broadcast their London basement disaster. The groundworks contractor ignored all the warning signs right from the start! They took lots of chances that the excavations would not collapse with no support in place. After completing the excavation, the groundworks contractor started the concrete works. It was at this point that the excavation failed and the concrete formwork broke down! Leaving the clients with a very expensive hole!
This horrible introduction to basement construction devastated the clients. They needed something to get them back on track to prove that living in London can be viable and sustainable!
Saving the Concrete Construction
Through our reputation for safe, strong construction and good client relationships, the clients asked us to come in and survey the hole! With the clients now miss-trust in the construction industry in mind we mapped out a safe and secure rescue plan for their dream house. They needed a reassurance. Proving our worth to the future of the small building we immediately made the excavation safe.
We started with sheet piles, strong supports, fencing off and a total health and safety review. With proper procedures in place we could start removing the broken timber shoring.
Now under control, Grand designs London and the client came on site. Visibly excited we had successfully given the client his dream back and Grand designs a great story!
Small Building in Grand Designs
On the footprint of three garages in east London, we were to build a basement on which a three-story house would sit. With the use of steel sheet pile groundworks supports we could excavate to full depth without having to cross the property line. With the excavation complete we started addressing the concrete disaster left for us. Due to previous concrete formwork fails, the concrete came into the basement space by up to half a meter in places. MJ Rooney had to break back and render all this to protect the now exposed reinforcement. Thankfully we could then do what we do best and create a beautiful concrete construction. The small building needed as much space as possible so it was important that all our levels were correct and the concrete face flat and smooth.
Seeing the transformation from a health and safety nightmare to a concrete construction build with real pride and standards put everyone involved at ease.
Floating Concrete Slab of the Basement
The floating concrete slab would provide a sub-ground floor that would help us to fully insulate it from the exterior concrete construction. This was done with a unique bracket that sat on insulated blocks. Having a floating mass of concrete insulated within the house would then act as a storage heater. This concrete mass would slowly get warm throughout the day and then release its heat during the night. Construction of the floating concrete slab consisted of timber formwork from below. The unique thermal brackets were then mechanically fixed to the concrete construction. MJ Rooney tied one side into the reinforcement of the floating concrete slab. Then we poured the concrete into the formwork and once it cured permanently, we set the brackets in place. Unique to this build, the floating concrete slab will help the build become passive.
Passive House Design
A passive house is a highly energy-efficient structure. Not only the finished house but the construction of the house is scrutinized and held to a much higher standard than normal housing. As a basement contractor, we specialize in separating the finishes from the structure. We do this for waterproofing and thermal bridge avoidance. Our experience in this field helps us to give advice and create designs within the concrete construction to enable the passive house design.
With a mass concrete underground structure, creating a passive house design is somewhat of a challenge. As described above, we had to insulate any internal structures from the concrete construction. We needed to use the right materials with the floating concrete slab. You might think that concrete is not the right choice for an environmentally conscious build. But used correctly, it can actually store energy as well as lasting more than a lifetime.
Waterproofing the Basement Structure
The primary waterproofing is the structure itself! For this reason, we put the water bar strips into all construction joints. These will swell if water comes into the joint and block its passage. Good concrete, well mixed and compacted, will reduce water ingress to an insignificant level. Then, we install the internal waterproofing. The internal environment needs to be completely free from water or damp. The cavity drainage system ensures no free water into the structure. Then we need internal environmental controls to keep moisture away such as condensation.
MJ Rooney chose a cavity drainage system as the internal form of waterproofing for this project. We attached a dimpled waterproofing membrane to the internal faces of the basement walls and floor. Any seepage through the concrete construction would travel behind the membrane. Then into drainage channels, it will be pumped out of the building.
To get other ideas, check the swimming pool that we constructed in a basement below an existing house located in the Kent countryside.
