The joy of dealing with damp - please can I have some advice?

MuddledOfMiddlesex

I'm in the process of trying to buy a 170-year-old house. The surveyor noted damp in different areas of the property and I've now had two further reports done by contractors: one report I paid for and one I didn't. Both were by local firms.

The one I paid for found more extensive damp, roughly matching the surveyor's report: the damp proofer's report notes that two areas are have 'high' levels of damp, with the rest just being described as 'areas of damp.' These include areas upstairs as well as downstairs - the areas where levels are high are both on the back wall of the house.

The other damp proofer only noted the two areas of 'high' levels of damp. Their quote is a third of the price of the other's.

I think the cause is that the house is a terrace with a further set of terraces at the back, where garden walls abut the back wall of the house and are at a higher level - that's bridging, am I right?

Both damp quotes recommend membrane treatment. One (the more extensive one) recommends Delta PT and the other cheaper one doesn't name the product but also recommends injection with DryZone at the same time to bases of the walls.

I'm pretty confused. My plan would be to get the work done on completion, before moving in. But that was when I thought it was to two rooms. If it's to pretty much all the rooms, it gets much more disruptive. My questions are:

1. Do those treatments sound appropriate for bridging (or whatever the proper name is for being affected by damp due to neighbouring properties being closer)? And is that really likely to be the cause of damp upstairs as well as ground floor?

2. Is there a case for having the 'high' levels treated and then waiting to see what the other areas are like when I move in? The house doesn't smell damp and I haven't noticed any significant plaster damage.

I really don't know the best way to go. I'd really appreciate any advice.

David_Aldred

Hi,
I appreciate the reasons why you may be confused but in all honesty I don't think you are going to get the answers to your questions from a simple post on here where at best we can only guess at possible causes to the problems you have at the property.

A couple of things to bare in mind might be that chemical damp proof courses are only designed to control rising dampness to a point that is perceived to be neligable and are not in general designed to resist moisture moving under any form of hydrostatic pressure. The significance of that is that they may not be able to resist moisture bleeding into a solid brick / stone house wall from a garden wall built directly into that house wall and in such cases if the garden wall cannot be isolated from th house wall then some fom of structural waterproofing may also be required.

Secondly the rate of drying down once you resolve a moisture source can be quite slow and at best 25mm wall thickness per calender month is probably the best rate of natural drying down you could hope for.

When choosing a contractor to undertake the work I would always recommend a Property Care Associaton (PCA) Member be asked to inspect / quote or alternatively if you want an independent opinion one of the (PCA) Freelance Surveyors local to you. Kindest regards David Aldred damp & timber surveyor

Gloomendoom

Is the damp currently causing a problem.

I only ask because I live in a very old house and what might be regarded as excessive damp by new build standards can be a complete non issue in the context of a very old house.

Of course, if you have mildew and toadstools growing indoors you will need to address the problem asap.

MuddledOfMiddlesex

Thanks, David and Gloomendoom.

David, I take your point. What is structural water-proofing? Is that something I'd need to get the neighbours to do/need access to their garden to do? Or is it something more like the membranes? Or are membranes damp-proof courses? I thought dpcs were when you inject chemicals?

Gloomendoom, I don't think it's causing big problems. I certainly didn't notice anything when I went there. But the surveyor did add a retention for the mortgage loan so I guess he's worried enough about it.

David_Aldred

Hi MuddledOfMiddlesex,
Sorry for the delay in responding I have been on holiday and just picked up your query.

A damp proof course (dpc) may come in various forms such as:

1. Sheet material be that modern pitch polymer (looks like black plastic sheet) or say a bed of bitumen / slate / lead in older houses.

2. A layer of the masonry itself if relatively impervious such as a layer of hard dense engineering brick or stone.

3. Electro osmosis where wires are embedded into the wall to resist rising dampness.

4. Chemicals injected into the wall (the most common type of retro fit dpc) to resist rising dampness.

5. Syphonic pots or specially shaped bricks inserted at set intervals horizontally into the base of walls.

The intention of the above is to provide a layer at the base of walls that would prevent or control to a point that is perceived to be negligable the tendancy for ground water to rise up the wall by capillarity (think of a sheet of paper with its bottom edge lowered into a glass of water slowly soaking that water up the paper).

Sometimes however houses will have situations where moisture is actually pushing through the materials the house was built with to a point that is unacceptable. Examples of this are say where walls are not thick enough or built in such a way as to prevent wind driven rain penetration, or there are external defects that may be difficult to resolve / outside your control, or a basement wall surrounded by a high water table or where an adjoining property is built higher than the subject property.

Structural water-proofing may be applied externally or internally and are where systems are put into place to say hold that moisture back (for example by applying tanking slurry), or deal with that moisture once it enters the property (i.e. internally applied cavity drainage membrane systems) in such a way that the moisture is not apparent to the occupier.

Although you may need access to the neighbours property to undertake certain methods of structural water-proofing in some situations, this could also be undertaken from your side only of say a party wall but there is legislation you should comply with such as the Party Wall Act and also there may be a liability if a person structural water-proofs on their side of party wall and that action causes an increased level of dampness / decay and in a worst case possible flooding in the adjoining property.

The above is by no means an exhaustive explanation but I hope it goes some way to illustrate some of the differences between a damp proof course (dpc) in the base of walls and the purpose of structural water-proofing. For further information on chemical dpc's reading a copy of BS6576 and for structural water-proofing BS8102 both of which should be able to read on line at your local library may be helpful. Hope this helps, kindest regards David Aldred Independent damp and timber surveyor.