Case Study: Basement Conversion Playroom Harrogate

Basement Conversion Harrogate - Playroom

Danford Brewer & Ives undertook a basement conversion on a property in Harrogate during the spring of 2018.
It is a terrace house, constructed of stone, with a slate roof, brick chimney, UPVC guttering, wooden windows and stone flag floors.
The owner’s intention was to convert the basement into a playroom for his children.  They also wanted a utility room, a toilet and two storage areas/cupboards, each separated by internal walls from a landing that leads to a new staircase.
The process was as follows:

  1. Damp Survey

We first needed to ascertain what level of damp the existing basement had. The survey was restricted to the basement and our readings (taken with the aid of an electrical conductivity-type moisture meter known as a Protimeter) revealed evidence of rising and penetrating damp to all areas, as well as water ingress.
Two major causes of the damp were the high ground levels and structural abutments, so we recommended that either the external levels were reduced or an internal barrier, incorporating a waterproofing agent or membrane, was applied and fixed to those areas - at least up to the level of the newly installed damp-proof course.
(NB We did not undertake a structural survey and always recommend that any worries/queries regarding such issues should be resolved using a suitably qualified person.)

  1. Structural and basement waterproofing

All structural and basement waterproofing work was undertaken in accordance with British Standards Document BS 8102:2009, the code of practice for the protection of below-ground structures against water.
It specifies a level of protection (grading from 1-3) based upon the end use of the conversion. In this instance, since it is being used as habitable accommodation, the required grade was 3.
One assumption BS 8102:2009 makes is that ingress will occur during the conversion’s lifetime - caused, for example, by a change in the water table, drains becoming blocked or heavy rainfall causing localised saturation.
After careful consideration of various methods of controlling persistent water entry, therefore, we recommended installing our cavity drain system to all areas indicated on the plan.

  1. Drainage

The cavity drain system’s effectiveness is based upon discharging free water, before pressure builds behind the system.
For this to be possible, an effective and fully maintainable drainage system was installed.

  1. Preparatory Work

The existing ceilings were stripped, with plumbing and electrics relocated in the ceiling.
Some timber repairs were required in the utility area. Where there were signs of deterioration, the timbers were cut back and replaced by either steel support brackets or resin ties.
The existing opening into the floor void was increased to approx. 2.4m wide by installing a new concrete lintel (that was subject to a structural engineer’s approval). An area, approx 1200mm back into the void, was then lined with a membrane and framed out to form a new storage area.
The existing single skin brick wall in the utility area was removed (no structural replacement was required) and the stone staircase was broken out and also removed.
We lifted the existing stone flagged flooring, which was kept for the client, and the floor was excavated by a depth of approx. 100mm to allow for the build up of the membrane and floor finishes.

  1. Waterproofing

A sacrificial screed was poured incorporating a 100mm x 75mm perimeter rebate. Once the floor was cured and prior to membranes being installed, the concrete was treated with an anti-lime coating to stop the build-up of free lime within the cement and prevent the drainage from blocking.
The walls were lined with an 8mm studded Cavity Drain Membrane. This was installed to at least the height of damp course level.
A perimeter drainage channel was installed, complete with servicing flushing points. The drainage falls and collects within the sump chamber and any water build-up is discharged via the twin pumps located within. Each pump has its own independent fused spur supply.
Once the drainage and pumps were installed, we flood-tested the system.
The floors then received a 20mm CDM which was sealed to the wall membrane as required. The system was then flood-tested again.

  1. Fit out

To be compliant with current building regulations, and as the basement is a habitable space, insulation was required (our specification was subject to Building Control approval).
We laid a minimum 50mm close cell insulation board on top of the floor membrane and covered it with a 22mm water-resistant floorboard.
The external walls of the basement were lined with 75mm timber frames and fitted with 75mm rigid foam boards. The internal walls were battened out using 50mm x 25mm timbers.
We also installed a new timber staircase.
A toilet area was formed under the stairs, supplying a new WC and basin. The foul waste collects in a chamber within the utility room and discharges into the nearest foul waste drains externally.
The ceiling received a 100mm wool insulation and all surfaces were then lined with a 12.5mm plasterboard.
The rooms were fitted out with a softwood skirting board. New doors were fitted to both the living area and utility room.

  1. Fixing to or through the waterproof systems

When fixing through the membranes, careful consideration was taken, including the possibility of an alternative method.

  1. Non-earth retaining walls

We carefully marked the position of the fixing at the required point and drilled. We filled the hole with a high-quality mastic and then inserted a propitiatory plastic fixing plug. More sealant was applied around the hole to form a seal before inserting the screw.

  1. Earth retaining walls

Specialist fixing plugs with purpose-made seals were used in order to maintain the integrity of the membrane.
It is important that the flushing/service points are easily accessible so that regular maintenance can be carried out to the drainage system to ensure that no blockages occur. Maintenance programs are available and are a condition of the guarantee.
As the works described involve a Party Wall, the Party Wall Act 1996 was therefore applied. This requires the owner of a property to notify his/her neighbour(s) of the proposed works and obtain the neighbours’ consent. A neighbour cannot unreasonably withhold consent, but should you require further advice or information, please initially contact our office or a suitably qualified party wall surveyor.
Danford Brewer & Ives are very aware of Health & Safety issues and dangers within our industry. Any work that we carry out is done so safely, in the best interests of our customers, the general public, and ourselves.
Guarantees
Upon completion of our specialist remedial works and full settlement of our final invoice, Danford Brewer & Ives issue a 10-year independent insurance-backed guarantee.
The client was thrilled with the final results and tells us the children are using their new playroom all the time.  If you have any plans to convert your basement into additional living space then contact Danford Brewer & Ives for expert advice and support.
Here is a short video showing how the project progressed and finished up.
https://www.youtube.com/watch?v=461GGEh6QMg


Basement

Basement Conversion Cost

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