While we’re pretty sure that, for most of us, a trip down to the basement might not be the stuff of cheap horror film nightmares, neither might it be particularly pretty. At best, a tumble dryer, fridge freezer and an iron/ironing board might be lurking down there. Mainly, though, it’s pipework, lots of clutter, paint peeling off dripping brickwork and a fusty smell.
Your basement might be full of things you’d half-forgotten about, just lying there gathering dust or going mouldy in the dank, dark air. In general, we don’t want to spend too much time down there. But if we think about it, the biggest thing lurking down at the bottom of those rickety wooden steps is something less tangible and clearly way more useful than a VHS recorder: it’s the potential of the place.
Just think a whole new living space. What might you do with it? Okay, you’ll probably have to go to the tip to chuck those old paint tins, and those toys the kids have grown out of will have to go to the charity shop. But you can fix the damp and give yourselves more space. Potentially much more space.
You also need someone who can do the job – which is where we come in.
There are two schools of thought here. The more traditional method involves simply sealing the basement using cement based products, which holds the water back. However, that also means pressure gradually building on the structure; for this method to be effective in the long run, then, drainage really needs to be dug outside.
By contrast, cavity drain membranes work by placing the drainage on the inside; using this method, the water ingress is controlled by the plastic membrane. Water then drips down the outside of the membrane, gathering in a drip tray-style drain before it’s routed via a sump pump to an external drain.
It’s an ingenious method, in that it prevents a gradual pressure build-up against the internal construction, while an air gap behind the membrane allows the structure to ‘breathe’ and dry out.
Yet it’s also simple and uses simple materials. The membrane itself is usually a high-quality, high-density plastic such as polyethene. It is studded in appearance – thus allowing room for the water to drip down to the drain – and comes in various thicknesses e.g. 3mm, 5mm, 8mm, up to 20mm for the floor membrane.
The material will also be gas and vapour-proof and can have a long-lasting guarantee e.g. 10 years.
The wall membrane is applied using fixing plugs and then the drainage channels will be created around the basement perimeter, leading to the sump chamber.
After this, the floor membrane will be laid, again for waterproofing. Vapour tape is then applied where the wall membrane meets the floor membrane. This implements a secure moisture barrier between the seams and also helps strengthen the joints, keeping the membrane firmly in place.
The ‘tank’ – the seal – is now complete, but let’s rewind for a moment. Earlier we mentioned the sump pump, which will be installed at the beginning of the process i.e. when we have our basement shell and before the membrane is applied. The pump will be fitted in the sump chamber, which will be at the lowest point of the basement and connected to the drain channels underneath the membrane walls. The groundwater is then pumped out from the chamber to an external drain.
With a lid on the chamber, screed or timber floors will be laid over the membrane whilst leaving the sump perfectly accessible.
The walls are then finished by dry lining in which metal or wooden frames are installed allowing for electrical or plumbing services to run out of sight.  The walls are then insulated, plasterboarded and skim finished as required.
Since ‘basement tanking’ is strictly our expertise – and a basement conversion is often required as part of a larger project, we’re an ideal partner for builders, architects and property developers.
If that’s the case, then sub-contracting this particular aspect of the work to us makes sense for all manner of reasons…
For example, we offer attention to detail: analysing the project and writing a specification after agreeing the finer points with the architect.
We can also assist developers in making the best possible use of available space and land. It might be necessary to provide underpinning if the conversion of a basement compromises the structural integrity of the property by weakening the foundations or removing walls, for example.
Moreover, we are skilful, efficient and cost-effective.
As you can see, the potential is enormous. By making use of our expertise, both householders and building partners can gain living space and add value. Basements don’t need to be left to clutter, mould and old copies of TV Quick.
A little imagination can go a long way…

So, how much will it cost?

A typical basement conversion in the Yorkshire, Cheshire and Teesside area is usually in a Victorian terrace with an existing space in the basement. These basement rooms are usually cold, damp and badly lit. Provided the existing head height is adequate the price guide is between £700 – £1,300 per square meter. If the conversion works require any digging out, excavating or underpinning the work becomes more complex and more expensive. Underpinning usually costs between £1,500 – £2,000 per square meter.
To help you understand and get an idea of how much your basement conversion might cost we have provided 4 possible basement scenarios. Each one is based on 30m square of space below ground in a Victorian end terrace house.


Option 1. Simple Basement Conversion

This basement is a single room with 3 external walls and 1 party wall. The head height is more than adequate at 2.2m. The room is currently being used a garden/ store room. In the winter periods water appears to rise up through the stone flagged floor and is leaving the space continuously cold and damp. There is an existing solid stone staircase leading up to the main house and a small light well to the rear of the room.
Using a cavity drain membrane system, we will transform this space into a warm, dry storage area.
To achieve this we will install a perimeter drainage channel with flushing points at each change in direction. As there is no natural drainage present we will install a sump and pump with a high level battery alarm system. The drainage and pumps are fully maintainable and when combined with cavity drain membranes forms a waterproof structure to comply with current British Standards 8102 (2009) – The code of practice for protection of below ground structures against water from the ground. Your basement is now ready for the ‘fit out’ stage.
A new insulated timber floating floor will be installed and the walls lined with independent timber studs. The 1st fix electrics for the supply of a new socket and lighting circuit will be carried out along with plumbing alterations to add a new radiator. The walls and ceiling will then be plaster boarded and plastered to a finish. The electric and plumbing works will be finished and signed off as required. The basement conversion works are now complete and ready for decorating. As this space will only be used as storage Building Regulations do not apply and therefore insulation is not a requirement.
Summary.

  • 4 walls, room area approx. 30m2
  • Cavity drain membranes to walls and floor
  • Drainage channel and mechanical pump system
  • Timber floating floor and studwork
  • Plasterboard and plaster finish
  • Electrics & Plumbing
  • Party Wall agreement
  • 10 year Independent, insurance backed guarantee.

Estimated Cost £ 21,000 + VAT (£700/m2)


Option 2. Standard Basement Conversion

A standard basement conversion would involve the same works as Option 1 with the addition of needing to have Building Regulations as the space is now to be used to provide an extra living space for the property. This will include the addition of insulation within the studwork and ceiling areas. There is also the inclusion of an internal load bearing wall that would require lining with cavity drain membrane and studwork.
Summary

  • 4 external walls (30m2)
  • 1 Internal (load bearing wall)
  • Drainage channel and mechanical pump system
  • Timber floating floor and studwork
  • Insulation
  • Plasterboard and plaster finish
  • Electrics & Plumbing
  • Party Wall agreement
  • Building Regulations
  • 10 year Independent, insurance backed guarantee.

Estimated costs £25,500 + VAT (£850/m2)


Option 3. Complex Basement Conversion

A complex basement conversion has all the detail as standard basement with the addition of a more sophisticated pump system which includes a secondary pump with battery back-up. This type of basement conversion would also include digging out and creating a new external doorway with concrete access steps. Creating this opening would most likely require planning approval.
Summary

  • 4 external walls (30m2)
  • 1 Internal (load bearing wall)
  • Drainage channel and mechanical pump system with battery back up
  • Timber floating floor and studwork
  • Insulation
  • Plasterboard and plaster finish
  • Electrics & Plumbing
  • New external doorway with concrete steps
  • Party Wall agreement
  • Building Regulations
  • Planning permission fees
  • 10 year Independent, insurance backed guarantee.

Estimated cost £39,000 + VAT (£1300/m2)


Option 4. Complex Basement Conversion with Underpinning.

This type of conversion requires increasing the existing headroom. To achieve this the internal floor slab will be excavated to the required depth. The existing foundations will also require extending. This is done using a process called underpinning. With the help of our Structural Engineer we can design and specify the detail required to carry out these works in a safe and controlled manor. Once the underpinning is complete the drainage and membranes are installed and the fit out completed.
Summary

  • 4 external walls (30m2)
  • 1 Internal (load bearing wall)
  • Drainage channel and mechanical pump system with battery back up
  • Concrete floor and studwork
  • Insulation
  • Plasterboard and plaster finish
  • Electrics & Plumbing
  • New external doorway with concrete steps
  • Party Wall agreement
  • Building Regulations
  • Planning permission fees
  • 10 year Independent, insurance backed guarantee.
  • Underpinning and excavation works

Estimated cost £76,500 + VAT