Of all the wrong routes I’ve seen homeowners take during my years in the industry, this one takes some beating.  And the really sad thing is that the present owner knew nothing about it at the time he bought the house; he just happens to be the one picking up the tab.

The story involves a 1920’s semi-detached house in a northern city; let’s call it Manchester.

The street the house is built on has a water table with an ambient level that must be just below the kerbstones on the pavement.  It really is rather high. All the gardens have life-buoys on poles and seagulls drop in for sustenance whenever they’re migrating.

For years, the sub-floor spaces beneath the suspended timber floors must have been, variously: wet; very wet; and too wet to go out without your raincoat.

In common with most 1920’s houses, the airbricks would have been inadequate, both in number and in size and over the years their inadequacy, together with the tempest beneath the floors wreaked havoc on the ground floor joists: they rotted, and rotted and rotted.

About twenty years ago, the then owner, probably because he fell through the floor and landed, a la Dr Foster, up to his middle, decided that enough was enough, and he embarked upon a course of action that was to prove ruinously expensive for my client.

He, or perhaps his 'building advisor' decided that ‘timber floors bad’: ‘solid floors good’.

So, all the joists and floorboards were ripped out and they proceeded to fill in the swampy chasm beneath with a mixture of sand, cement, gravel and anything else that happened to be on the back of the builder’s truck.

The consistency and merit of this infill bore little resemblance to anything remotely useful.  In one corner of the living room it was sand; in another it was gravel; the centre had a little of both plus a smattering of cement; and the whole was well-seasoned with bits of wood, old cement bags, part of a super-market trolley (not really) and (honestly) some rather unusual underwear (gender unascertained).

This amalgam of delights was heaped into the old sub-floor space to a height that just about covered the original damp proofing course.  But he (they) weren’t finished yet: in order to provide the whole thing with a scintilla of decency, they covered this porridge with a heavy-gauge polythene layer, on which they then dumped a screed, which had just a passing resemblance to something that would provide a hard surface for the carpet.  I estimate it was a mix of approximately 25:1, dull, fine building sand to cement. A worm could have tunnelled through it with ease.

And I simply gave up trying to understand his idea of level.  Either he had one leg shorter than the other or he drank Coca Coma for breakfast (aka White Lightning).  It was at least six inches higher in the living room than in the dining room, and it generally had more humps than a camel’s tea-party.  There was definitely more in common with a funfair ride at Blackpool than anyone’s conception of a useful floor.

But its unusual construction, eclectic consistency and manic appearance paled into insignificance beside its poisonous ability to render both this, and the house next door, virtually useless for the normal purpose that bricks and mortar usually serve, i.e. living in.

The somewhat aerated consistency of the main fill soaked up the ground water like I, on certain occasions, can soak up Timothy Taylor’s finest nectar; only stopping when full to bursting. And as this concrete morass had unquestionably bridged the original dpc, it was now able to relieve its excess liquid into the brickwork and plaster above. 

Now, if anyone tells you that moisture doesn’t soak into bricks via capillary action and then rise up the wall, don’t believe them.  This property has probably the best instance of rising dampness ever experienced in any building since my maternal grandmother installed a swimming baths in her front parlour.  But that’s another story for another day.

Every wall in every ground floor room (bit of hyperbole there, there’s only a kitchen/diner and living room) was wet to the point where mushrooms were sprouting; gastropods were slugging it out to see which one could climb highest; and the willow pattern wallpaper was weeping copiously.

A dreadful state of affairs, with my client’s distress only interrupted by the next-door neighbour’s fury; a fury I have to say which was pretty understandable.  My client’s ‘monster in the deep’, not content with wrecking his walls had also laid claim to the party wall between the two properties and was performing similar miracles of transformation on that too.  The poor neighbour, unaware of the debacle next door had re-plastered his side of the wall twice, and every time he did so, out popped the salts, and up rose the tidemark.

The party wall in the unfortunate neighbour's house

So; the only course of action now left for my utterly traumatised client is to bring in the digger men; remove the porridge; re-install the suspended timber floor; and increase the amount/size/efficiency of the airbricks. Cost? Probably in the region of fifteen to twenty grand – ouch!

Moral of story? Never, never, never fill in suspended timber floors; just because you, or especially the builder from hell, thinks it might be a good idea at the time.  It isn’t, and it never will be.  The void beneath timber floors plays a vital role in ventilating the ground floor walls, and you mess with that at your peril.

If your joists have rotted: replace them with pre-treated timber; protect their ends where they rest in or on masonry walls; and finally, improve sub-floor ventilation. If your solum is simply exposed virgin earth, lay a Heavy Gauge Visqueen sheet over it, but only if you have an effective dpc in your walls. If you lay Visqueen and you haven’t got a dpc, ground water will be re-directed into the base of the walls and, well, see above.