My basement is not very wet, so do I really need a great deal of work?
Well, while a specialist can consider existing conditions and give balanced advice, the British Standard to which we work - BS8102 - states that one must act as though ground water pressure will come to bear at some time during the life of the building. Also, while as far as you are aware your basement may have been apparently dry to date, there may be hidden existing drainage below the floors (very common in Victorian houses because they copied the way the Romans did it in forming channels below solid floors) that will be disturbed by any new works, particularly if the floors are dug out.
Indeed making any changes in a basement can disturb the equilibrium that has existed for years, so what was just a damp basement can easily become a wet one with water standing. This often occurs where existing reasonably drained but damp floors are taken up, with new concrete laid on a polythene dpm, resulting in free passage of ground water being blocked. So instead it emerges under pressure up at the wall and floor joints. A BS8102 specification will include waterproofing to both floor and walls to prevent this and create a fully dry space.
Surveyors report on property I am considering buying states
Tanking is normally specified for basement and cellars which are wholly below ground and where the problem is lateral water pressure from the surrounding ground.
In the case of ground floors tanking would not normally be used unless there is a problem with high external ground level causing the same type of pressure as in a basement. If this ground cannot be lowered, then it will be necessary to apply appropriate protection to the walls and floor using either a cementitious waterproof render or a cavity drainage membrane.
If rendered the wall will need to dry out fully before you can redecorate but the membrane system can take a plasterboard dry lining which can be decorated without delay.
However the surveyor?s report is not entirely clear as the problem could be a failure in the damp proof membrane under the floors and/or rising damp in the walls. Best to commission a survey from a specialist damp control surveyor.
With the tanking process what happens to fitted kitchens and cupboards? Do they nullify the process?
Fitted kitchen units need to be removed to enable a tanking system to be installed to the walls and floors of a below gound room. After installation they can be re-instated but the fixing method must not under any circumstances puncture the tanking, whatever its construction, otherwise it will fail. A specialist contractor will be able to advise the specification to employ.
We own a Victorian terrace about 200m from the Thames. There has always been water in the cellar and now we have dry rot. We have been told ours is a flood cellar (it is about 6 foot in height) - is this true? Does the water need treatment?
The term 'flood cellar' is not a familiar one but given the property's proximity to the river, it is likely that the cellar was originally incorporated to relieve potential water pressure on the structure.
If as you say water is always present, there is a strong likelihood that this has given rise to condensation forming on the floor timbers above and this in turn has created the conditions for dry rot to develop. The dry rot will clearly need attention and measures taken to prevent recurrence, eg introducing a constant air flow.
The water should be changing if the river is tidal but if not and the water is stagnant, there is certainly the risk of contamination and it would be advisable to get it tested.
Contact your local water supplier for advice on this - they may also be able to give information about the history of water ingress into properties in the vicinity.
I had a new garage built four years ago and included a pit, six feet deep. For the last year the pit has had two to three inches of water on the floor. It is difficult to dry out. What materials and solutions are available to resolve this problem? Thanks
If water is a consistent feature, it is likely to be a water table issue. Whatever provisions, if any, were made when the pit was constructed, they have clearly proved inadequate.
Water tables are rising generally which is why it is advisable to make suitable provision in all below ground structures such as cellars, even if no water is currently present.
Resolving the problem in your case calls for a specialist multi-coat waterproof cementitious render applied to the floor and walls of the pit. This is not a DIY job and requires the involvement of a professional contractor specialising in this type of work.
Is a damp proof course ,as opposed to 'tanking', adequate to keep a basement flat dry?
No, a damp proof course is designed to prevent moisture from the ground rising up via capillary action into the walls of the building. It will not stop lateral water ingress.
In a basement or cellar situation the problem is moisture under hydrostatic pressure from the surrounding ground and this can range from simple dampness to running water depending on the circumstances. The solution is to install either a cement based waterproof render to the walls and floor which will hold the water back or a cavity drainage membrane lining which is designed to channel any moisture coming through the wall into a drainage system around the base of the walls and under the floor and then move it safely away to the outside of the building, usually via a sump and pump arrangement.
How much will it cost for a basement conversion ?
This is really a case of 'How long is a piece of string ?' Because it's impossible to answer this question without knowing the size and specification of the basement you wish to convert, what you intend to use it for and so forth.
If you contact our nearest office - 0800 789 500 - and ask to speak to a surveyor, we may be able to give some ball park figures which could help you decide if it is a project you seriously wish to pursue. If the financial paramaters are feasible, then a survey can be arranged to determine and cost a specific conversion plan.
What happens if I puncture the floor membrane and how much is the repair cost?
If it's a studded plastic cavity drainage membrane on the floor and you puncture it, in principle the waterpoofing protection will fail. In practice the consequences will depend on the extent of the underlying water pressure and the efficiency of the sump and pump drainage system which is designed to remove any running water that may occur.
If this is working properly and has the required capacity, it should give some protection against water breaking through to the finished floor level. But if the property is susceptible to floods, this could easily be overwhelmed.
If there's no sump and pump, you potentially have a serious problem.
It calls for a specialist surveyor with the necessary waterproofing qualifications to assess the damage, advise on the best method of repair and provide a quotation.
My basement was waterproofed with Oldroyd Xv 4 years ago. The pump failed , went unnoticed and a serious flood ensued. There is now green mould over everything and about a foot up the walls. Will a new installation be necessary or can it be fixed?
You are best advised to contact the firm who installed this cavity drainage membrane system in the first place, because the flooding may have caused damage to the seals, particularly at the wall to floor junction, in which case it could well need to be renewed.
The presence of mould confirms the continued presence of a high degree of moisture so it needs investigation.
It is also worth noting that a dual pump installation is always preferable (together with an alarm system) to guard against pump failure because, as you now appreciate, the consequences are serious.
Will concreting over a small front garden help damp in the cellar directly below?
Yes, to some extent˙if water is penetrating˙the cellar from above.
BUT˙the predominant cause of dampness in a cellar is˙lateral water pressure from the surrounding ground and without the installation of a waterproof system to the floors and walls, this will continue unabated.
If anything, concreting over the garden will increase the risk of water penetration because˙it will mean the faster run-off of surface water˙which currently˙tends to be absorbed by the garden and so released more slowly. (You may have read press commentary˙on this point in discussions about the increased incidence˙of flooding in built up areas).
Can you tell me whether you carry out your cellar conversions to comply with building regs?
It all depends on the use to which the converted cellar will˙be put but assuming that it will become an additional living area - 'habitable space' in building regulation˙terms - then all work has to comply with those regulations and prior consent˙obtained from the local council.
The actual waterproofing system employed will be installed to comply with British Standard BS8102.
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I'm looking for some independent advice. I want to build a basement next to my house, but not under the existing property. Above the basement will be a ground floor, a first floor and a loft conversion. The water level was 1.5 metres below the ground in the summer, so it's pretty wet out there.
I have spoken to several basement companies and there seem to be 2 schools of thought, one saying waterproof concrete and backfilling; the other saying cavity membrane system and pump. Both say theirs will do the job, but I'm not sure. Can you help?
Designed and installed correctly both systems can do the job ! The advice you've been given probably reflects the particular preferences of the different parties involved.
The key requirement, whatever the specification adopted, is that the design complies fully with BS 8102. In Peter Cox we mostly use cavity drainage membrane systems but not always. The systems differ in that cementitious renders are designed to resist˙the water pressure and prevent moisture ingress whereas the membrane system allows water entry but channels it away in a controlled manner via a sump and pump system.
For the project described you will probably need the services of an architect or building surveyor and it would be their job to advise on the best method of waterproofing for the specific circumstance faced. But even the professionals have their preferences !
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Is the only fix for water pressure under my basement concrete floor new footer tiles ?
It depends on what use you wish to put your basement to but if you plan to convert it into a habitable space, then it will necessitate the installation of a proper waterproofing system to both the walls and floor. The choice will be between a waterproof render˙designed to withstand the water pressure or a cavity drainage membrane which channels any moisture into a˙floor sump and pumps it out of the building.
If the intended usage is merely for storage and you can accept a degree of dampness, you can just renew the flooring. However˙this will merely have the effect of diverting˙the water to the nearest weak point so the risk is that you could start to see moisture˙appearing up˙the walls.˙˙
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