Mould/Damp on ceiling Query

CatFromHue · 17-07-2025 02:30PM #1

We had an extension put on in 2017/18 that extended the bedrooms out, roughly drawn below. This involved adding an air vent to the back wall as well. Over the last year or two I've been noticing mould starting to build up near the vent and a few spots of discolouration on the inside of the extension where the wall and ceiling meet. I'm worried that this might be more than just a bit of mould, the room is very warm naturally, and there might be a bit of a leak. There's a few cobwebs in the first pic but you can see the mould around the vent. Does that look like a bit of a leak?

ted1 · 17-07-2025 02:58PM

probably just a cold soy on the wall. I assume you clean the mould off when it’s appears.

You could look at a electric/ mechanical vent with a built in humidistat

10-10-20 · 17-07-2025 04:24PM

Probably the block used for the closing the cavity at the top of both leafs. Even pumped cavity insulation suffers for the thermal bridge at that point.

Monitor and Manage the RH and open windows when you can.

CatFromHue · 18-07-2025 06:43PM

Thanks for your comments. Below is a few close up pics of the affected area. It's the middle one that had me thinking is it more than just some mould.

whizbang · 18-07-2025 09:50PM

Thats a water stain in last 2 pictures.

Have a look up above in Attic.. Is this a flat roof ?

CatFromHue · 19-07-2025 01:51PM

This room had the extension put on so there's no attic or room above it. It's not flat as there's a small angle to it. Just got out the ladder and took a picture looking into the building and then from the window looking out. To my untrained eye it looks ok.

ongarite · 21-07-2025 01:07PM

To my untrained eye, the bottom tile to the right of the skylight is broken.

It’s the finger width one, looks to be broken in half. And the tile beside it isn’t flush, sitting correctly because of the flat roof raised edging

10-10-20 · 21-07-2025 02:17PM

https://www.boards.ie/discussion/comment/123656408#Comment_123656408

The skylight will have been fitted with a skirt under those tiles which should extend around 30cms from the edge of the frame, so that area should be well sealed. It should be checked all of the same.

I wonder if it's leaking around where the flashing meets the render. That area is supposed to have the lead-work tucked into the wall with retention-clips fitted so that it's all tight, then sealed up afterwards. I can see where some of the render has been repaired over to the right of the soil downpipe.

Here's an example of what I'm talking about, except you haven't lost the mortar/render.

https://www.youtube.com/shorts/nLSHaEt3wdA

whizbang · 22-07-2025 12:20AM

Not sure how the pictures match up.. is the Velux in the room you show the mould pictures?

The roof tiles should have been fitted over the upstand of the of the left and right skirt frame, but its not a big concern.

The lead flashing mentioned above should be dressed under the flashing where it meets on the angle joint between tile and flat.

CatFromHue · 22-07-2025 08:48AM

In the first picture of the outside the wall the black pipe going upwards was the existing outside wall and the extension was built on to that. So the pictures of the inside with the discolouration/mould are where the inside wall/ceiling meets that wall i.e. directly below the black pipe.

The vent in my first post is just out of shot in the first pic of post number 6.

10-10-20 · 22-07-2025 09:18AM

https://www.boards.ie/discussion/comment/123658481#Comment_123658481

What is that black pipe anyway? It's a prime suspect if it's where the moisture is.

whizbang · 01-08-2025 11:41PM

Lift the flashing around the green area and have a good look - chances are water is gathering there. The white area needs the 45degree angle flashing over the top of the horizontal flashing. Red area needs sealing. Yellow area is a concern; Needs sealing but difficult to get right due to movement etc.

Mould/Damp on ceiling Query

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