What is this mysterious wet patch on my wall? (Photos)

[HouseSquirrel]

Bought a house in August. It's about 15 years old and has a single storey extension at the back, added in 2017. Now that the weather is cooler I notice that there always seems to be a wet patch on the outside wall of the extension. It seems not to be coming from the guttering, and it's there even when it hasn't been raining. There is an outdoor tap on the wall, but it's below the wet patch. There is no sign of damp on the inside of the wall. Any ideas?

The attached photos were taken on different days.

And some more photos ...

Aaaaaargh ... should mention that the close ups of the guttering in my last-but-one post (i.e. the photos taken from above) are mirror image because I took them with the selfie camera!

I think it's the dip and joint in the gutter. Tricke water into the space between those two clips with a jug.

Gutters should be straight, and sloping slightly and evenly down to the end with the downpipe.

The presence of the Velux might be relevant, but if, say, the flashing is not right, the water should be caught by the membrane.

Start asking round for a well-established local roofer (by personal recommendation, not an advertising website, especially if it's disguised as a recommendation site).

...and scrape out that moss and other material. If there is a lot of spare membrane, you can cut away the excess with kitchen scissors. It's hiding the joint, but I think it's been wrongly made.

here's an example of a gutter joint.

they vary a bit between brands.

here's an old fellow. It's not me. Don't use glue or sealant, because the gutter is meant to slide in and out on the rubbery seals when it expands and contracts with the weather. He indicates the lines showing where to insert the lengths with a gap in the middle.

Thank you @PigletJohn! I am asking around for a roofer ... it's only just stopped raining so I will try the targeted trickling water with jug investigation when I get home! And the gutter needs replacing anyway, so it makes sense to do that any hope for the best ...

The thing is, it might look like it is draining away when raining, or being filled with a hose. But what you might have is a very slow drip, either from the back of the gutter (as a previous poster suggested) or from the join. If the gutter is slightly tilted, the drop of water will slide under the gutter and down the wall, rather than dropping on the patio. Water is a funny thing, it doesn't necessarily do what you expect it to!! (P.s. We have has this too!).

Just a thought..... and possibly cheaper. If you have a good window cleaner, he should be able to sort it for you. Mine did.

gutter is available in 4m lengths, I don't know if you do the whole lot on one, but of course, the fewe joints the better.

Use plenty of supports. The joiners are meant to screw to the wall. There is a way of making a special bracket to support a drooping end if there seems nowhere to screw it.

The gutter is dipping down at the joint.

This will mean that when it rains heavily (as we've had recently) the water can't get away through the downpipe and will over flow......down your wall.

The gutter union needs to be raised so it falls to the outlet without a back fall.

Thank you for the insights/advice ... might have to try the window cleaner option as I haven't had a response from the roofers I have contacted (a friend who works in the area said that they are inundated at the moment after some bad weather).

Thing about the dripping-from-the-join idea ... the guttering is some way clear of the wall. It stands a few cm out from the white bit (the soffit?), which in turn stands some way clear of the wall. Looking at it from underneath, I can't see how water that dripped from the guttering could get to the wall - and the wet patch starts right at the top of the wall. But since people here obviously have more experience than I do, and the guttering needs replacing anyway, that makes sense as a place to start!

clear out the moss and rubbish for a start, and have a look at both the front and back clips for a start.

But I think the joiner has been fixed to the wall too low (if at all) hence the dip and the bad seal.

Its quite a simple fix to straighten the gutter, I'm sure the window cleaner armed with a cordless driver will be ok if he's half compentent.

When the water overflows that heavily it tracks down the fascia and amazingly, across the soffit also. Next time you have a real downpour check it out :)

Sorry I haven't read all the replies, but your photo reminded me of my own wall that I posted about recently.

I think/hope mine is now resolved. I had 3 roofers take a look at it and one found a partly broken tile (underneath some lead at the side of a dormer window) and under the tiles there were some holes in the roof felting.

So the rain water was getting under the tiles and then pouring down inside the wall. Mine actually seeped through to the inside wall too.

Still waiting for it to dry out completely to see if it is fixed.

Just thought I'd mention it.

Has something similar before, similar bricks. It was a leak dripping inside /in the wall cavity, soaking wet insulation when they took a brick out. It did not come from an external leak.

In our case it was a leak in the pipe from the boiler to the external vent dripping condensation into the cavity. They had to remove bricks to trace the source

If it's not the gutters, what is on the other side of the wall? Are there any pipes hidden in the wall that could be leaking?

Maybe a cracked tile on the roof above the damp patch.

My dad came to visit and immediately diagnosed the problem Will get some silicone sealant stuff and see if that solves the problem!

Meanwhile a local roofer quoted £350 to replace the guttering which was more than I was expecting ... 4.5 metres of straight guttering, easily reachable with just a step ladder. Going to try the window cleaner, as a PP suggested!

perhaps an additional problem, but water does not run upwards.

Well, there are gaps further up the window too ... if I fix this (and the guttering) then hopefully any further wetness will be easier to trace, if there is any.

Also, some soaking upwards might have happened? I noticed this patch of damp above a neighbour's front door.

pigletjohn although water doesn't run upwards, it surely can travel in any direction by capillary action? So it's worth considering other options as the source if leaks/overflows from higher up turn out not to be the problem.

in clean, unrendered brickwork, with cement mortar joints, capillarity doesn't go up by more than about two bricks.

I don't understand capillarity, but I'm told it's due to the different pore size in mortar and bricks.

Mineral salt deposits into the wall from groundwater can make it worse.

Render, plaster, and rubble in the cavity enable it to go higher.

Exposure to air (such as an external wall) makes it rise less because it reaches equilibrium at the height where the water evaporating off equals that rising from below.

The wall in the pic is modern and in good condition, and has a particular isolated patch extending downwards, from the point where the gutter looks to be defective, so that's where I'd go first.

Attached are two pics of experimental walls. In clean water, with good mortar, it hardly rises. The second is after standing in water containing mineral salts for four months (you can see the white efflorescence crystals)

Capillary action can be demonstrated with two cups and a piece of string or strip of cloth.

Fill one cup with water and then drape the string/cloth from the full cup to the empty cup.

Leave for a few hours and when you come back, the full cup should be emptying, there may be a puddle around the two cups and there should be water in the once empty cup.

Dry areas will 'draw' moisture up or, if the water pressure is high enough, wet will travel.

Water is strange and creepy stuff. It can get to places you'd never think to look.

Nothing to add, but at water being creepy.