103J: peace of mind survey following repaired shower leak

Client waited 4 months for a peace of mind survey during the Covid lockdown winter of 2020/21. The end of terrace house had been extended. A ground-floor shower was leaking (repaired before the survey) causing water to be absorbed through to the extended porch and recycle by condensation onto the cold external porch wall.

Surveyor Tips:

  • Peace of mind surveys are some of the most interesting and most appreciated.
  • Here I showed the client a simple technique for testing for a leak from the mains water that every survey should consider using.
  • The explanation was complex and detailed but appreciated by the client.

Root cause

Shower leak fixed before survey, condensation.


The first concern was dampness in the porch. There is crystallise salt on the surface.

The salt is calcium sulphate, a key ingredient in cement and mortar. If diluted in water salts tend to move to surfaces. These can be removed with sandpaper and decorated. There is also a brown, teabag stain like discolouration, a sign water has passed through brickwork.

Using a damp meter, where above 20WME is damp, I determined that there is some residual damp.

This low level of damp indicates that the wall is drying out on the internal side of the porch.

Client image of wall during cold snap in February.

On the external side of the wall water appeared on the wall in a symmetrical rectangular fashion. There were dribble marks. This is a sign of condensation on the cold sections of wall. If there was penetrating damp, that is rainwater from the outside, there would probably be a brown stain. Vapour from the internal wall is condensing on the coldest part of the porch.

Looking through a thermal image we can see the same regular shapes. Blue is about 5°C colder than yellow.

The porch appears to have been constructed of large breeze blocks. The mortar loses temperature rapidly, compare to the blocks. 

You sent me this image after you discovered and repaired the leak on the other side of the porch wall.

It was clearly very damp some months ago.

I measured the inside of the wall with a damp meter, it is only just over 20 WME therefore drying.

Walls dry from the surface inwards towards the centre, at a rate of about 1mm per month.

I use the same damp meter with radio frequency mode.

Radio waves at a set frequency can identify damp deep within a wall. They cannot differentiate between water and other dense matter. I found damp up to about 1.3M. There is much debate about how to dry a wall fast. From a practical perspective, if water is free to evaporate from the porch wall, I think you can re-tile the bathroom before the centre is dry.

There was rot and woodworm in timber under the plaster wall.

The rot was probably Coniophora puteana, or cellar rot, a brown wet fungus, and wood weevil, see surveyor.tips/rot. Rot requires water to grow. Wood weevil requires rot. Remove the water and both will stop damaging timber. The floor has been replaced with a solid floor so there is no realistic risk of rot continuing to grow.

Looking on the outside there are cracks in the render up to the roof, which should be filled.

Your builder should rake out and fill cracks (an external acrylic caulk for small gaps and similar material to the original render for larger gaps >1-2mm). The remove flaking paint and repaint with a suitable masonry paint

The render should be taken down to the bell drip, that is the metal support in this image.

Consider increasing the triangular skirting at the base of the wall with a cement mortar.

There were dribble marks in the rear corner of the side extension.

This dribble marks are a sign of condensation from insufficient ventilation and to lesser degree insufficient heat or poor insulation.

There was a high damp meter reading up to about 1 M.

Looking outside there are a lot of cracks around the adjoining wall.

And I don’t believe that the cracks are causing penetrating damp but they should be filled. The wall will act as a thermal thin increasing heat loss and therefore risk of condensation.

I measured the extractor fan rate, which is less than building requirements of 15 l/s, but not too bad.

The problem with the extractor fan is it switches off once lights are turned off. I recommend replacing it with a continuous flow extract fan see recommendations.

Other matters

Ideally the kitchen should have an extractor fan especially as it is internal, opening onto the conservatory.

It could be a challenge installing the fan in the kitchen so consider other methods of minimising production of vapour, see recommendations

I tested for a mains water leak. There were no signs of an ongoing leak.

It is worth using this neat trick to regularly test for a mains water leak, see https://surveyor.tips/leak-tracing/

I would fill and paint other gaps around the property such as by the front door and front window sill.

The upstairs bathroom does not have an extractor fan. There are signs of mould growth.

Consider installing a bathroom extractor fan, see other practical recommendations.

There were streaks caused by water coming down the chimney breast in the loft.

Looking outside, the flashing appears to have lifted up for the left-hand side.

This is not a roofing report. I believe the most likely cause of dampness in the loft is this flashing. If the flashing is lead, it can probably be remoulded back into place by a competent roofer. However if they are going to charge you for scaffolding, then it would be worth replacing the lead and putting up a cowl (top to chimney pot), and ask them to check other aspects of the roof at the same time.

Leave a Comment

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.