I just wrote a post on my www.basementwaterproofingexpert.co.uk blog relating to discussions with a local supplier, who advised me that Manchester basement conversion firms are building in risk to systems by omitting battery back-up, this on the basis that clients would not pay for it.  It's a poor design choice and I feel for the clients that sooner or later will suffer floods as and when ingress occurs during a power cut.



Another post on my http://basementwaterproofingexpert.co.uk/ blog.

This post relates to the numerous failed cementitious slurry tanking systems that we deal with and the fact that in many cases, these are installed by non-specialist contractors backed by suppliers that provide an approved status.  Tanking is not a simple or easy task and failures do occur.



Firstly, apologies for the overly dramatic title but hopefully this will provide a useful example of the implications that a basement conversion can have on a property, where the work and guarantees which stand behind it are questionable.

In 2009 I took a call from a homeowner with a townhouse property in Manchester, they had just converted their basement / cellar to a habitable space, employing a local cellar conversion specialist to undertake the work.

There had been a few hiccups with work along the way, and while this was partly unrelated to the basement waterproofing, they advised that there were visible damp issues and as a result they had lost confidence in the waterproofing installation.

The homeowners had not yet paid in full and we were asked to inspect and provide advice in respect of what had been installed and works required to resolve the outstanding issues.

When I inspected it was fairly typical (at least at that point in time) in that cavity drainage waterproofing had been installed but there were no inspection/maintenance ports for the drainage channel system, and no evident battery back-up system for the sump pump – this meaning issue in the event of power cut – with omission probably motivated by cost. It was definitely a less than perfect spec.

In addition there were minimal areas of low level bubbling paint finishes, staining and efflorescent salts.  The general patterns indicated moisture penetration and certainly warranted further investigation.

I subsequently provided a written analysis and list of considerations which needed to be addressed. The main aspect that I stressed is that they should resolve the issues, pay the outstanding money and… get their guarantees.

I heard nothing further from the client and assumed that all was well.

Fast forward to 2015, and I’m asked to inspect a basement conversion with possible issues by a Manchester Building Surveying Practice and so off I go.  I meet the homeowners, walk downstairs and there I am, back in the basement in question!

I ask the homeowner if they bought it from my previous clients, which they did, and then I start looking around.  I can see that some of the issues (plumbing) have been resolved, but still no inspection ports or battery back-up, and while I could see evident redecoration I could still see the staining, there was now deterioration in timber floor finishes at the wall floor junction to the perimeter, high % moisture content readings from softwood timber skirting boards across a fairly wide area, also efflorescent salts causing paint to bubble and debond from the skim plaster it is applied to.  If anything conditions had worsened.

Efflorescent salt deposits form when water moving through the ground and/or building materials, dissolves salts contained within those materials.  These are held in solution, however when that moisture evaporates, i.e. changes from a liquid to a gas, the salts return to a solid state and form a crystalline deposit.

I don’t know what happened between the homeowner and the contractor but clearly the issues were not satisfactorily resolved.

I sent a copy of my original report to the Chartered Building Surveyor and discussed the considerations.  His first thought was obviously that of his own client and that if the property were purchased, what would it cost to correct, with the objective of ensuring no future issues, and addressing in a manner whereby we could provide guarantee?

With cavity drainage systems the key is in ensuring that the drainage element included within the floor construction functions as intended to collect and channel water to the means of removal, in this case a sump pump system.  We can only guarantee that which we treat and so as a minimum the work would have involved opening up, stripping out to expose the structural slab and most probably improving the detailing before replacing the waterproofing system (membrane/pump/channels) so that we protect the floor construction and low level wall areas.

This was not a small space and included a bathroom.  I estimated the costs at £25,000.00.

I can only assume that the prospective purchaser asked for a reduction or walked away, probably the latter.

This is the thing.. if any member of the public calls me asking about a basement conversion with issues and/or no/questionable guarantee cover, my advice would be to consider the implications very carefully, in that personally I would not seek to buy what are potentially expensive problems.

It makes more sense to purchase a property with a basement/cellar which has not yet been converted, than one which has been converted but has such issues.

This is because there may be a substantial cost in stripping out (in this case losing expensive timber floor finishes etc.), before you can even start to correct the waterproofing.

Note: I’m not publishing photos of this basement as that would obviously not be fair to the current owners – hence the redacted feature image!

You might think that such situations are a rarity, but I’ve just advised on a converted basement apartment in Didsbury, Manchester with issues where they got the installer back to remedy under guarantee then had me get me back out again because the repair was poor.

At the time of writing I’m working on a failed conversion in Altrincham where we are stripping out and renewing the cavity drainage waterproofing system to the floor construction, where they installed only one length of channel, ran that into a gravity drain and the system failed. The specialist installer can no longer be contacted so the homeowner is having to spend £9k with us to have most of the work undertaken again.

The full article can be found on:


I just answered this question and thought I'd post it on our blog. The question:

Hello there
I think your website and the advice you give is simply the best that I have ever seen.
I am in a bit of a position in that my other half is a (very good) builder but not versed in basement conversions – not his bag nor does he want it to be HOWEVER in true builder style he wants to do the work on our cellar but I am wary of the methods that he wishes to employ as he feels it is a ’dry’ cellar and I know from reading countless online forums that there isn’t really any such thing!
He has already, some time ago, dug down to increase head height and then insulated and concreted the base of the cellar. Other than that, no work has yet been carried out…
I am unable to bring in anybody else for fear of upsetting the apple cart but neither do I want a job done that will only have to be re-done at a later stage.
Any advices would be gratefully received.
Many thanks in advance,

Our answer:


 There is a British Standard, ‘8102 (2009) Code of practice for the protection of below ground structures against water from the ground’.  As an approved code of practice this sets the minimum standard required for waterproofing in the UK.  If we installed systems and there were issues with those systems, our design/installation would be compared against the advice detailed within it.  If we didn’t comply and the client took us to task, we would probably be found liable.

There is guidance within the standard that as a designer, you should consider the risk that any below ground space will come under groundwater pressure at some point in its lifetime, even when site examination indicates dry conditions.  The standard advises that we should consider things like the effects of climate change (increasing rainfall) and burst water mains / sewers.

So yes, it may well be dry now, but may not always be that way.

It may also not be that ‘wet’ but the retained ground externally will always receive rainfall, and while it might not ever become saturated leading to liquid water penetration, the ground will always be damp and the probability is that the retaining walls hold capillary dampness as a result of the damp ground which bears against them.  At present this dampness may evaporate readily from the wall surface.  If such walls/floors are lined out with plasterboard, timber, carpets etc. and other materials sensitive to moisture, they may well deteriorate in time, even where liquid water penetration does not occur.  Worst case, liquid water penetration does occur and the space floods.

In conclusion, if you convert it without giving sufficient consideration to waterproofing, the risk will be that deterioration will occur and you will have to strip out, waterproof and then fit it out again, with the investment in time and funds on the original fit out, strip out and second fit out being lost.

The space should comply with the Building Regulations and should go through a building regs application with the local authority so that you obtain a completion certificate recognising the change of use to habitable space.

If you do not waterproof correctly, and do not go through building regulations, this might cause complication in the event that you then look to sell the property.  This because I, and others would typically not recommend purchasing or paying full value for,  converted, but not waterproofed / approved by the LABC space.  In other words I would advise prospective purchasers not to treat it as a finished habitable space, and to accept that if they have future issues, they will have to foot the cost of stripping out, waterproofing  and all the works that follow to get the ‘habitable’ space back.  You may therefore lose the investment in conversion even if problems do not occur.

Building regs. also includes means of escape in the event of fire, which on a safety basis is more important than the waterproofing.

A few years ago we remedied a residential converted basement in Altrincham, where a couple had purchased a property with the basement already converted.  One Christmas water started to penetrate through the floor and we were asked to investigate.  There was no waterproofing and the assumption had obviously been made that it was a dry space.  They had a very nice Italian rubber floor tile in there that matched the kitchen flooring over.  It was fully stripped out, with cavity drainage waterproofing being installed by Trace, before it was fit out again.  The project cost was circa £20k from memory.

 Hope that helps.

These are photos from the Altrincham project mentioned above:

Trace: Periodically we attend to a job like this, a basement conversion where the requirement for waterproofing was not fully understood by a general contractor, there is a lack of thought put in to design and the untrained staff installing have to do what they think best, which then results in poor detailing.

Water is unforgiving and in a wet space such as this, problems subsequently occurred.  At least in this case those issues arose before completion, and we were able to step in, design an appropriate solution which we were then instructed to install.

A degree of underpinning had also been undertaken in this case, and so we advised that a Structural Engineer be instructed to advise on that aspect.

This is one example detail (membrane installed the wrong way around): IMG_7808Our client writes:

Back in Spring 2012 we decided to get our cellar converted into a much-needed extra room.  We had visions of a spacious office where my wife could run her business, I could work from home occasionally, and we could reclaim our dining room from computer equipment and filing cabinets.  Our “cellar” did not exist as a room, it was just an earth filled cavity under the house, but we knew it should be possible to dig down, providing the foundations were deep enough.

We had previously used a well regarded local builder for our attic and kitchen extensions, and had been very pleased with his work, so we decided to employ him for our cellar conversion too.

The work began with 3 trial holes to check the foundation depths and the state of the soil.  Good news, the ground was dry, so excavation and construction started.

Spring and Summer 2012 were the wettest recorded for many years, and it rained pretty much constantly throughout all the digging, which did not help.

Things began to go awry fairly soon.  Two or three streams were discovered running under our house, probably they had always been there, but unfortunately they had not been spotted in the trial holes.  They were running freely so we hoped that they would not affect the cellar if they were left undisturbed.

As work went on we were concerned about the amount of water sitting under the membrane, and there were several other problems, but work was completed despite delays due to the weather and our addition of extra rooms (scope creep!).  We had got as far as decorating before water started seeping in.  Our builder was constantly returning to try to patch up leaks, and things came to a head when water found its way under the floor and the whole room gently rocked and pitched like a boat at sea.

At that point we decided that our existing builder couldn’t sort out the problems, and called in Trace Basements.

James Hockey, Lee Davey and his team were very helpful and we discussed several options, but as we investigated further it became obvious that there were too many things wrong to fix without starting pretty much from scratch.  All of the existing work had to be stripped out, right back to the mud and concrete and bare walls.  It was very depressing.

We now have a pump system installed to manage the water flows, decent drainage channels, much better membranes and seals, and are finally able to use the rooms.

Looking back on the whole process I think we were rather naive, and did not anticipate any of the problems.

Here is the advice I would give:

The finished space:

image003 - Copy

So, about three weeks ago we inspected a property with a substantial basement space which had been 'converted' into habitable living space.  We would expect that the total value of the property was in the range of half a million pounds, with the basement being almost full footprint, which gives an idea of the scope of the conversion.

The reason for our visit, was that the property had changed hands and the new owners required advice on the basement which was converted by an unknown builder for a previous owner, which was now leaking.

In opening up, we found that whomever had undertaken the conversion had included extremely poorly designed & conceived means of drainage, which had clogged up in a relatively short space of time, with this affecting the living space over via low level deterioration of plaster wall finishes and mould growth, caused by water penetration through the included cavity drainage membranes.

The design was so poor that a large proportion of the work will require stripping out and replacing in order to provide a dry living space which will remain dry in the long term.

So, having identified the brand of the cavity drainage membrane installed, we called up our local supplier representative of the brand of membrane/system installed, who we know well and like a great deal, to give him what-for on behalf of the new owner who now has an expensive problem to contend with.

The rep appreciated what we were saying, but also stated that they cannot help it if people do not do what they are advised to do, such as 'including sump pump systems' - which for the uninitiated is a necessity on any project where the structure is fully below ground, and where the intention is to keep a space dry...

The issue is that there are contractors who do not know what they are doing and either through ignorance or choice, cut corners or implement poor designs which ultimately costs the consumer in a serious way, when basements flood.

So, if you're successfully selling waterproofing products and are doing very well thank-you; and are approached by general contractors to buy your products, what can you do other than try and give best advice even if they do not follow it?!

I don't blame suppliers because like us they must sell products or services to survive, and you can't take full responsibility for what others do, but it is a fact - and we are seeing this more and more - that consumers are falling foul of these situations, and they are the only ones losing out !

We received a call from a client in Cheadle Hulme, Manchester, advising that the sump pump alarm was operating.  Our Service Engineer attended the property out of hours at the clients request to check over the system.

BBC News reported:

'Heavy rain storms have led to severe flooding in parts of Greater Manchester'.

'People living in Stockport and Cheadle Hulme were thought to be the worst-hit, as a flood warning was issued for the River Bollin catchment area'.

'The Environment Agency said Knutsford, Wilmslow, Hale, Macclesfield and Bollington could also be affected'.

With regard to our waterproofing system, this was working hard but sucessfully protecting the habitable basement space, with the alarm indicating that the system was close to capacity, but with no issue occurring.

This system is over 12 years old, but being serviced annually by Trace Basement Systems so that it continues to function and protect as it was designed to.  We continue to innovate and provide increased protection to our clients, and in this case have offered upgrades to the client in question to double their protection.

I wonder how many basements were not so fortunate.

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