Damp Question

[Anonymous]

We own a ground floor purpose built flat in a 2 storey Victorian house built sometime between 1890 and 1901. We live in London near the Thames in Putney. The rear of the house was extended, and although the council have no record of plans, we have been told that the type of construction material indicates that the extension was done shortly after the house was built. The extension has a concrete floor and we have found that after heavy rains the floor becomes damp causing the wooden flooring that has been laid over it to buckle and rise.

We contacted a number of damp companies all of whom observed the following:
- it is not clear whether any damp proof layer was installed under the concrete floor of the extension;
- the patio outside is too high and is therefore breaching the damp coursing in the walls;
- there is little surface damp on the interior of the walls;
- there is damp within the walls, but this is not unusual because they are not cavity walls.
These companies suggested digging a french drain about 1 foot from the wall, and covering the concrete floor with a membrane before putting carpet/wooden flooring down.

However, we have had one specialist who told us that we don't have rising damp but suggested that the house is built over an aquifer or other body of water, that the water levels are rising and that the walls throughout the flat, internal and external, are saturated. He has told us that the plastering throughout the flat is "tank grade" and that the extension would have had damp proofing installed when it was built. He has suggested:
- having tests done to determine the "moisture profile" and level of salts in the walls (i.e. drilling small holes to the core of the brickwork);
- that if there is a problem the walls could be injected with a solution to stop absorption of water and to allow the walls to dry out.

Please could you help with the following:
1. We don't know who to believe - none of our neighbours have had this problem (it is a terraced house), and it was not picked up in the survey when we bought the property. Also, the problem only seems to manifest after heavy rains, and only one person out of the 6 that visited us have identified this as a problem. Can you recommend someone who can give us a second opinion?

2. If the walls are saturated, is the injection method the best remedy, and how much is it likely to cost?

3. If the walls are injected with this solution, what happens to the brick work below the level of the new dpc? Presumably they will remain waterlogged and therefore will become badly damaged. Are we at risk of the foundations being weakened?

Many thanks

Duncan

 

[Anonymous]

Hi Duncan,

Been thinking about your problem a bit. Difficult to advise when I can't inspect the extension.
Anyhow, let me answer some of your questions.

1. I think it would be better to presume that no damp proof membrane is under the concrete floor and no damp proof course in the walls.
2. The patio height will cause dampness by allowing water to cross through the wall, thus causing internal dampness. The patio height needs to be reduced or dig out section of patio and line the junction of the wall/patio with 1200g of polythene sheet to stop water pentration.
3. The little surface damp on interior walls sounds like a condensation problem. Do you have black mould forming on the internal surface of the wall and does the extension feel cold? The construction of the wall is not cavity, therefore when applying internal insulation a void (Min. 50mm wide) is required between the existing wall and insulation. Can you insulate the extension externally?

You say none of your neighbours have these problems and that a specialist suggested the extension may be built over an aquifer with water levels rising. If the plaster is tank grade then previous owners/developer have identified dampness/water problems, hence use of tank grade plaster. One thing you could check is the water table and whether this has risen over the years. If you dig a trial pit about 1m away from extension, dig about 600mm deep. If this pit fills with water whilst digging and does not drain freely then you have hit the water table. If you see no water then the ground conditions are normal. If water is evident then you will need to install a permanent water control system and seek advice.
Is the existing ground conditons boggy and water logged?

I have supplied a link for you which could be what you need to resolve the problem. It's a floor and wall cavity drainage system, not sure of cost, but would be worth getting someone from this company to advise you further. This link takes you to floor section and you can download the "Oldroyd interior walls" brochure from there (wouldn't allow me to attach info to this message). This product is mainly used for basements, but they also deal with above ground level.

Let me know how you get on.
Regards
Claire



www.safeguardeurope.com/products/oldroyd_xs.php

 

[Anonymous]

".....heavy rains the floor becomes damp causing"

I would have expected damp problems in the main house if it had been built on waterlogged land.

Have you had the rain-water drains checked? The extension was probably built over existing drains. You can trace the route with a dye, lifting drain covers to confirm the direction of the drains. If the drains are suspect, you'd probably be best advised to get a CCTV survey.

 

[Anonymous]

Surely there is no rising damp because this is a not existing phenome in masonry with fine pored stones and rough pored mortar joints. This construction obstructs any capillar activity between stone and mortar.

So there must be another source for the damp. Normally its condensating humidity of the air. When it rains air humidity is high, so this would be a possible reason that condensate from warm humidified air comes into the colder floor.

My tip: Heat it out. In such cases we install a small heating pipe some inches about the floor level around the inside of the facade walls. This causes only IR radiation on low level but this will be enough to warm up the floor higher than the humidified air. Details on the link.



Dampy old houses - what to do?

 

[Anonymous]

Would it not be cheaper and sightlier to use a humidistatic dehumidifier to lower the RH, thus preventing the condensation occurring?

NT

 

[Anonymous]

That may be. But the IR radiation heating system works also as heating- your suggestion not. Onto about 4 °C outdoor temperature only the heated pipes keep the rooms in my house warm enough for living, when it gets colder, additional radiators begin by thermostatic control (sorry, I don't have the correct technical terms, but I hope you can understand what I mean).



Something about IR radiation heating (in german)

 

[Anonymous]

Both hot pipes and dehumidifier will give off heat. The dehumidifier will give off very much less, and thus use much less energy.

If your pipe is run by electricity, the DH will be much cheaper to run, as nearly all the required heat will come from the lower run cost central heating.

If your pipe is run by the CH, run cost will be fractionally lower, but installation cost will be quite significant, unlike a DH.

The main advantage I see with a DH is it doesnt only dry the place where the pipe runs, it prevents condensation in every part of the room.

also your system does not get rid of water, it just moves it back into the atmosphere. This will only increase RH. The DH does extract it, day after day, removing a lot of water and reducing RH.

I think I'd prefer the dehumidifier myself. Cheaper to install and more effect. I'm sure your pipes will work also.

NT

 

[Anonymous]

I am planning heating systems also for museal purpose. There they have dehumdifying vents for the museum rooms. But in spite of this there can be condensate and mould effects on the inside of facade walls. If they are cooler than the air and there is some air humdidty f.e. by a visitors group, which is not cancelled suddenly by dehumidifiying the air, condensate must happen. And if there is no heating in the condensate filled pores of the wall (and there is never heating), condensed water can stay there a long time and mould can follow.

So our system can cause other effects and we use it in many old buildings yet. Mostly warmed by CH and using the whole existing system if one is there.

In a warmed wall never condensate can go in if the air is cooler. Thats one of the important aims of our system [german: 'Temperierung der Gebaeudehuelle' - warming up the buildings 'envelope'].

I recommend the dehumdifier for dehumdifying of humified construction (hum, sounds humourous, isn't it?), but not for permanent heating.

The picture shows former 'moulded' Bishops castle 'Veitshoechheim' where we planned the heating for mostly conservatorial purpose.



Heating and dehumidfying (german)