Damp Issues in Basement due to side of house

[Matty0682]

Morning,

I bought my house recently and the survey showed high damp readings in the basement on the side of my house. The side garden is also slightly higher than ground floor hallway, so surveyor advised to reduce the side garden level (I’ll dig down 30cm) and improve water run off as any water hitting the side of the house is running into the side foundation, probability causing the basement damp. Basically at the side of the property there are wall remnants from the previously demolished adjacent property 60 years ago and no path was ever laid.

So my question, what could I do to improve water run-off on the side? I was thinking about digging down (so that side garden is lower than hallway 30cm), then laying a patio slopping away from house with a drain gully on edge of property to take water away? I have asked a renderer for a quote to put a plinth at the bottom also.

Or do I lay contrate path? Or waterproof membrane with gravel on top? What would you all do?

Thanks

Matt

 

[JohnD]

Your cellar wall is in contact with the earth, so will always be damp. The wall may have a DPC. For a start, find it. The ground level must be at least two bricks lower than the DPC and your internal floor. This will prevent the wall above the DPC bring wet, and reduce risk of your floor joists rotting. The DPC must not be bridged by render, plaster, earth or paving, inside or out.

You might be able to make the ground less damp, if you put paving on it, sloping away from the house and also running towards the road, with a gutter to catch and lead away rain from the public path. You will never make the earth dry or lower the water table.

Look out for any nearby pipes or drains that may be leaking into the ground, and repair them.

You should ventilate your cellar to reduce water vapour.

It is possible, at huge expense, to apply waterproof lathing to the inside of underground walls so that penetrating water runs down to the floor, to excavate and drain the floor, and to add new false walls and floor on the dry side. You will not prevent water getting into the walls.

 

[Lower]

Did the adjacent property have a cellar that's been filled in? I'm guessing you're in plymouth so i'm assuming that it might have been bomb damage that caused the adjacent property to be removed?

 

[JohnD]

I've seen similar, and it used to be after bomb damage, but can also be redevelopment when part of a terrace is removed.

 

[Matty0682]

Thanks both, you are both absolutely right. Yes I live in Plymouth, I live in a row of three terraces in Plymouth (I am the end terrace). It was previously a row of 8 terrace houses, so the basement of next door is my now side garden.

They were not bombed luckily, Plymouth CC had compulsory purchase order on them in the early 60's and demolished them so that Armada Way can go all the way to the Hoe. Please see pic attached from 1959, my house is the red arrow, the 5 terraces to the left are demolished. Leaving my basement damp.

I am after the most affordable option in the short-term as we are about to pay for re-render (until we put more cash a side). So patio with a drain away may be a short-term plan not to make it worse. When we moved in, the drainage for the back roof was going into the side garden.

I'll dig out the survey, I don't think it has a DPC, rather the basement walls were 'tanked' (I don't know what that is. I'll find the extract on from the survey shortly........

 

[Matty0682]

This is the extract from the survey, it doesn't have a DPC, but the internal wall were 'tanked'. Does this sound reasonable advise?:

'Damp Proof Courses
Having regard to the age of the property there would have been no effective damp proof course incorporated in the walls or floors of the original parts of the property during its construction. Some basic slate coursing may have been incorporated but this only has limited effectiveness and is often omitted.

We were advised by a previous owner of the property that the walls around the majority of the basement were tanked during the refurbishment prior to being dry lined internally with independent wall linings. This cannot be confirmed. You should be aware, areas below ground level are susceptible to dampness problems and damp-proofing systems can fail over time. In the longer term, some further repairs and improvements may be found necessary.

Dampness is evident in various locations. You should be aware a property of this age, which does not have an effective damp proof course, will be susceptible to dampness. Further dampness problems may occur in other areas of the property over time.

The external ground levels to the side of the property and to the front and rear of the basement are higher than the internal floor levels. This is a common source of dampness and the ground levels to the side should be reduced where possible. It is not practical to reduce the ground levels at the front or rear.

Basements and Cellars

The property has a basement. There is a distinct musty smell on entering the basement area indicating some problems with dampness, condensation and ventilation. This is typical for this type of below ground location where dampness problems are common.

The previous owner advised the basement was upgraded as part of the historic refurbishment. We were advised that the majority of the walls were tanked, prior to independent wall linings being fitted. The extent and quality of any historic damp proofing in this area cannot be confirmed. You should be aware damp proofing systems can fail over time.

Walls of random stone construction, are not generally considered suitable for remedial injected damp proof courses, due to their lack of uniformity and voids, and therefore the only options for repair are limited to periodic re-plastering incorporating damp-proofing agents, or the isolation of the damp walls from the internal finishes by the installation of modern ventilated dry lining systems, such as ‘Newlath’.

 

[JohnD]

"Tanking" usually means coating the inside surface if the wall with a tarry, rubber or bituminous coating, intended to prevent water coming through the wet wall into the room. It is fundamentally unsound in basement rooms, because the water pressure at depth will push though the wall and push the coating off.

It has more chance of working if it is applied to the outside surface of the wall during build, so that water pressure pushes it onto the wall. Even then, I have known quite a few cases where reinforced concrete underground structures suffer persistent water penetration. The internal lathing is a treatment that protects the rooms even though water penetrates the structural walls and floor.

You can get quite good results when you pour a new concrete floor on top of a polythene membrane, because the weight of concrete holds it down, but water will still come though the walls. Unless you pump it away, the water can make a floor float like a boat.

Incidentally I have a neighbour who added a new concrete floor with DPM to his cellar, but it still floods in exceptionally high tides because the water table is higher than the floor.

unless you are able to construct a new protected room inside your cellar, you will need to reduce damp by constant ventilation, or dehumidifiers if you can afford the energy bills.

It is very likely that the walls of your house do have DPCs, just above where ground level used to be when the house was built, to prevent damp reaching any higher, and this is necessary to prevent the ground floor joists and skirting from rotting. In London, damp courses have been used for 150 years, and other towns and cities brought in similar regulations. IME slate does not wear out and lasts indefinitely, although it can have (relatively tiny) cracks, and is often defeated by ill advised bridging with render and by paving or flowerbeds carrying damp above the level of the DPC. Many charlatans make a handsome living by injecting chemicals into walls without correcting the defect causing the damp.

 

[Ivor Windybottom]

If it's been tanked then it shouldn't matter how damp the surroundings are, it should be isolated from the ground.

You could check what sort of drainage system is in place. There should be one, normally the water would flow down behind the internal walls, collect somewhere then either get pumped out or flow out by gravity. You may find there's a sump pump under a hatch in the floor, or it may be a cowboy job that never had one. Some would paint some magic miracle paint on the walls and tell you it's been "tanked". Life isn't this easy, but of course they'd have stopped trading before this became apparent.

Otherwise, if it can't be remedied easily and you don't want to rebuild the internals completely then keep the ground floor joists dry, below that basically abandon it. Perhaps add some vents, basically treat it exactly like the void under any house with a suspended ground floor without a basement.