Damp underdwelling - tanking recommended

[Deleted User]

I’m in the process of buying a Yorkshire underdwelling and the building survey has flagged up damp. It is in a low flood risk area. This was a damp and timber survey carried out by an independent surveyor who doesn’t carry out any damp works. The house has holes in the walls indicating previous chemical damp proof treatment, which this surveyor says is likely to have been ineffective. 

The survey states 45-100% damp up to 1 metre (seems a very wide range) and recommends tanking. The surveyor hasn’t recommended any companies to do the work. This is not just a cellar but a full home. Would this be a huge, disruptive and expensive job? Taking days, weeks or months? Thanks in advance for any advice. 

AdrianC

I'm not clear what you mean by an "underdwelling". Do you mean the property's external walls are below ground level?

If so, then - yes - they will be damp...

Tanking involves a waterproof coating over one side of the wall.
If it's the outside, water can't get into the wall.
If it's the inside, water can't get out of it.
Obviously, one of those is far more invasive on an existing property than the other...

Me? I'd buy a different property...

RAS

AdrianC said:

I'm not clear what you mean by an "underdwelling". Do you mean the property's external walls are below ground level?

These are pretty common on the steeper sides of Pennine valleys. The lower house is built into the hillside, looking over the valley, with another house built on top with access from the street. Some are through by light.

Another issue is noise as it's essentially the same as living on a ground floor flat.

stuart45

Probably similar to a basement flat. There was a period in the 80's when loads of the Regency properties in Hove were being sold off by landlords and bought up by developers to convert in to flats from run down bedsits. The normal method for the basement was hack off the walls, render, 3 coats of synthaprufe over the concrete floors and walls up to the ceilings and then another coat of render, skim and screed floors. Skirtings etc had to be glued on. nothing could be fixed by puncturing the walls.
When finished they seemed OK, but if you ever went into the flats after they had been inhabited, they always  felt really humid. 
Damp problems with condensation were really common.

FreeBear

Deleted_User said: The survey states 45-100% damp up to 1 metre (seems a very wide range) and recommends tanking.

You do realise that those numbers are worthless... 100% moisture is basically a bucket of water. 45%, you would be able to see water running out of the wall just by pressing a finger against it.

As there as already been chemicals injected in the walls that have been deemed ineffective, you now know that any more injections will be equally ineffective and a waste of money. Tanking the walls & floor internally can be done. There are a number of methods available..

Plastering the walls & floor with a bitumastic paint then going over the top with a waterproof render - Relatively inexpensive, but will crack if there is any movement in the walls..

Applying an EPDM sheet to the walls & floor followed by a render & plaster coating - Attention to the joints is critical.

Once tanked, you can never drill any holes in the walls & floor or you will compromise the tanking (there are ways round that, but...) If cracks appear, they need to be fixed fairly quickly and before any long term damage sets in. The space will always be cold and difficult to heat as the walls will suck up warmth - Adding a thick layer of wall/floor insulation (Celotex/Kingspan type) will go a long way to improving matters, but it will bump the cost up a little.

[Deleted User]

FreeBear said:

Deleted_User said: The survey states 45-100% damp up to 1 metre (seems a very wide range) and recommends tanking.

You do realise that those numbers are worthless... 100% moisture is basically a bucket of water. 45%, you would be able to see water running out of the wall just by pressing a finger against it.

As there as already been chemicals injected in the walls that have been deemed ineffective, you now know that any more injections will be equally ineffective and a waste of money. Tanking the walls & floor internally can be done. There are a number of methods available..

Plastering the walls & floor with a bitumastic paint then going over the top with a waterproof render - Relatively inexpensive, but will crack if there is any movement in the walls..

Applying an EPDM sheet to the walls & floor followed by a render & plaster coating - Attention to the joints is critical.

Once tanked, you can never drill any holes in the walls & floor or you will compromise the tanking (there are ways round that, but...) If cracks appear, they need to be fixed fairly quickly and before any long term damage sets in. The space will always be cold and difficult to heat as the walls will suck up warmth - Adding a thick layer of wall/floor insulation (Celotex/Kingspan type) will go a long way to improving matters, but it will bump the cost up a little.

Thanks for this very detailed information. Do you have any idea of an approximate cost?

AdrianC

RAS said:

AdrianC said:

I'm not clear what you mean by an "underdwelling". Do you mean the property's external walls are below ground level?

These are pretty common on the steeper sides of Pennine valleys. The lower house is built into the hillside, looking over the valley, with another house built on top with access from the street. Some are through by light.

So, basically, it is indeed three walls of a cellar... just with front access.