The Déjà Vu Basement Conversion that Lost the Sale / £25k Property Value.

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.  This is the space:

wet basement floor in converted cellar
Water penetration past the installed cavity drainage system (poor design), floor finishes had been lifted at this point.
basement conversion non-return valve
Cavity drainage with ill-considered design – drainage discharge to existing mains gravity drain. This is a non-return valve to protect against surcharge, the trouble with this is that if the non-return valve closes, water cannot discharge from the internal cavity drainage system, which would cause failure.

Last week I inspected a converted basement where it looks like mastic asphalt tanking to the floor and a slurry tanking system to the walls. Massive efflorescence coming through the walls and it appears that they did not prepare the brickwork before applying the slurry, which is totally incorrect. The specialist installer has had one attempt at correcting, but now wants the homeowner to pay additional for the tanking system to be replaced with cavity drainage!

In my opinion it is important both to get the work right and to obtain worthwhile guarantee. This work is not cheap whoever undertakes it, and the objective should be to undertake it in such a way that the investment is returned when the property is sold, this as opposed to the opposite situation as illustrated above.

There are many in the wider construction industry who put themselves forward as also being basement conversion specialists (with this being a source of work particularly during the recession), who have been supported by suppliers who’s primary concern is lining their own pockets, offering ‘approved contractor’ status to anyone that agrees to buy solely from that supplier – the Altrincham case above being such an example.

I really do not wish to generalise and obviously everyone has to start somewhere just as we did, but in cases such as the above, the public are being failed to their financial detriment and standards need to be raised. I’m happy to win work advising on and rectifying issues, but I’d rather failures did not occur in the first place, and my advice would be to aim high, pay for quality and look at the history and financials of those who offer to install.


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