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104W: Neighbour dispute averted

This architecturally renovated Victorian house had damp along the party wall. Naturally they assumed it was coming from the neighbours.

Surveyor Tips:

  • Keep your mind open, listen to owners, but don’t make assumptions until you have checked, in this case the neighbour’s side.
  • Minimise the risk of neighbourly disputes until you have sufficient evidence.
  • Think about the way a property and the neighbours side interact.
  • Check the inflow and outflows of vents.

Root cause

Condensation resulting from vents ducting into each other causing recycling.


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The original damp issue was caused by a leak to the pipe seen in the centre of this image.

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Using a damp meter I was able to detect damp from about 2.5M down to ground level.

I don’t believe I was aware you were drying clothes in this room. Clothes produce about ½ L per person per day. In my view you should have a continuous flow of air while clothes are being dried. I recommend an Elta Mori dMEV continuous flow fan, which provides 5 L/s of airflow with a 15l/s high humidity or light activated boost function, see actions.

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The worse of the damp is in the centre where there are surface salts and high surface meter readings.

My suspicions are that the water damage in the centre was caused by the original pipe leak. Calcium sulphate is puckering the surface plaster. Calcium sulphate which is also known as gypsum is a key ingredient in cement, plaster and other building materials. If diluted in water, salts tend to move to the surface. These can be removed with sandpaper, filled and painted when dry. The dry time could be months.

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It’s difficult to tell with this thermal imaging lens but the wall is cold and damp down to the ground.

The damp area seems to conform with the ground floor neighbours bathroom. It is probable that the ground floor neighbour is not heating their bathroom as much as other parts of their property, therefore this wall is at greater risk of condensation then for instance the upstairs bathroom wall.

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The extraction rate of the utility room fan is 7.8 l/ and only last a few minutes after lights are switched off.

Building regs. extraction requirements for bathrooms is 15 l/s for 30 minutes. Utility rooms produce similar amounts of vapour to bathrooms, but over a longer time period.

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The extraction rate from the external vent is 2.6l/s, therefore only 50% of the air is being removed.

I understand from speaking to you that a T-junction was added to the kitchen ducting. Therefore presumably 50% of vapour from cooking is going into the drying area and 50% of vapour from drying clothes is going into the kitchen area. Use two backflow shutters to ensure vapour is extracted properly.

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I visited the neighbours lower ground floor flat and found a shower on the other side of the damp wall.

It is possible that water is leaking through small gaps in the tiles. However, I could find no gaps and normally a leak would be accompanied by a stain which there isn’t on your side of the wall.

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There is rot on the floor by the bathroom entrance. This suggests that water is flowing across their solid floor.

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There is a washing machine in the alcove opposite the party wall.

I understand from the tenant that there was a leak and that the machine had to be replaced a few months ago.

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Looking behind the washing machine there was dampness on the timber floor.

I suspect that there is a small ongoing leak. Whether it is enough to affect your house is difficult to know, but it should be repaired anyway.

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There was measurable dampness deep within the neighbour’s side of the lower ground floor party wall.

I suspect that the issue is moisture on the wall increasing the risk of condensation on your wall rather than water flowing through. If water was flowing through you would expect to see discolouration on your side of the wall which there isn’t.

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I visited the upstairs neighbour’s bathroom but found no signs of a leak or damage to grout.

The 1st floor neighbour’s side of the party wall was drier on their side than in your utility room or the downstairs neighbour’s side of the same wall.

If the issue as coming from this first floor flat you would expect dampness on your side to start higher, for there to be one or two discrete points of entry and discoloration from water being drawn through a wall. None of these were present.

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I checked behind the upstairs neighbour’s utility cupboard, there were no signs of damp there either.


  1. Replace the utility room extractor fan with a continous flow fan such as Elta Mori, dMEV see https://surveyor.tips/extractor.
  2. Install two backdraught shutters, such as the “Kair Connector with Backdraught Shutter 100mm – 4 inch Non-Return Damper Flap” and probably 150mm – 6 for kitchen ducting.
  3. Monitor humidity and temperature against wall or ceiling, to see effects of improvements, such as ORIA Wireless Thermometer Hygrometer (20m (2 Packs)) – see surveyor.tips/datalogger. Ideally before and after changes, place one datalogger inside utility room and one in the kitchen outside.
  4. Monitor dampness with simple damp meter, logging at the same time and position every week, it will probably take many months to dry out.
  5. To speed up the drying process, dry clothes elsewhere, such as outside, at least until the utility room wall is dry. Consider directing a standard fan onto the wall.
  6. Ask your lower ground floor neighbour to repair the plumbing to their washing machine.


This report is provided to help the owner of the property as a courtesy, without payment or benefit from recommended actions and therefore without accepting any responsibly.

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