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.

I know you said it's not the guttering, but one patch of it does seem to be directly below a join in the guttering?

How exhaustively have you checked to rule it out?

Has anything been filled in the wall there? A vent or boiler outlet?

I’m thinking guttering also. Could you get a local tradesman to have a look?

@c3pu No proper investigation (still recovering from the expense of the move!) except for the homebuyer's survey which didn't pick it up. The guttering and the white part under the guttering is dry.

@fredafrogspawn I very much doubt it - it's a 2-year-old extension on to the living room. The kitchen is the other side of the house and so is the boiler, which is older than the extension.

@Imreallytrying Yes I expect I will need to :( Actually the guttering on the extension is leaking anyway (I think it's bent) but not over this bit of wall. Maybe I will borrow a a stepladder and take a look myself as a first move ...

skilledbuild.co.uk/how-to-identify-and-treat-penetrating-damp/?___store=default

This looks useful.

@fredafrogspawn Yikes - I hope not! It sounds unlikely from what it says at that site though ... usually on older walls and exposed conditions, whereas this is a newish extension and a sheltered position. (Extension was signed off by building regs btw.)

Would you be concerned that the survey didn't mention this? Or is it a case of 'well, it was summer, and if it was dry there was nothing they could do'? (I was planning to go for a full structural survey but the company I used persuaded me that it would be unnecessary given the age of the house.)

Just went out to look at the guttering ... pretty sure it's not leaking. It's also clear inside (i.e. not full of leaves/water/whatever).

It's almost certainly a leak in the guttering. Get the hose pipe out, put it on and fill the gutter, then you'll have it confirmed. If not you have damaged bricks or mortar. You can buy a clear product to seal bricks and mortar.

That’s a good idea.

I'd be suspicious about the pipe feeding the tap. If it happens when it hasn't been raining. Could be leaking and seeping up through the wall?

Hadn't considered that the water could leak upwards! When I'm not in my dressing gown I'll go and see if the water meter is turning round even when no taps are on. I wonder if there might be a way to turn off the supply to that tap for a trial period ...

As it's quite a new extension there should be a separate stopcock for that tap.

It just reminds me of a problem I had with a leaking pipe in my wall.

it does look like gutter. Go out when it's raining, or while someone squirts a hosepipe on the wall.

get on your stepladder and see if the underfelt throws the water intio the gutter, and if the gutter is fully under the edge of the tiles. The felt (or membrane) catches any water that gets between gaps or defects in the tiling

While the hosepipe is running, see if water drains away swiftly down the drainpipe.

If you can get a personal recommendation from a well-esatablished local roofer, they might spot the trouble.

squirts a hosepipe on the roof I mean.

you see where there are two gutter clips about a foot apart? Look closely at that part of the gutter. I think there may also be a dip, probably at a joint.

the stop end at the RHS is also drooping.

Pigletjohn is the Coleen Rooney of waterworks.

I expect Piglet John is correct.

We had a funny leak in this area. It was caused by the outlet from the condensing boiler (which drips all year) being incorrectly fitted and leaking acidic water which worked it's way underneath the extension roof tiles and dripping from behind the fascias missing the gutter completely.

Lol @ the Coleen Rooney of waterworks 😂

I really appreciate these suggestions! I hadn't realised that the water could potentially run down behind the gutter. Have asked Mr Squirrel to bring his step ladder over tomorrow.

I don't think it's the tap, btw. The water meter is certainly not going round when everything is meant to be off, which hopefully means we're leak-free.

Hmm ... It was raining this morning so I went out for a look (by standing on a stool and looking into the gutter with a mirror - no stepladder yet!). Looks like the gutter is clear and draining properly, not leaking as far as I can tell, and the membrane under the tiles leads into the gutter. After a few hours of rain the weather dried up and I noticed that the wet patch on the wall is no larger than it was before the rain, so maybe that means it's coming from somewhere else ... can't imagine where though 🤔

Look above the extension roof. Is there a bathroom, downpipe or boiler?

And please take some closer photos of the gutter where the dip or join is.

Is there a roof light or anything?

Thank you @PigletJohn! There is a bathroom on the second floor on that side of the house, and the toilet waste pipe is boxed in indoors. No boiler on that side. There is a downpipe, which you can see on one of the photos I'm adding, but it is maybe 10cm clear of the extension. There is, however, a velux window above the wet patch ... could it be the seal on that, do you think? No sign of wet indoors.

Attaching some extra photos (some in the next post!), including an outdoor one showing the downpipe and Velux, an indoor one, and some close ups of the join in the guttering.