Mould at the top of the walls

[obliquegeek]

Hi,

Just wondering if anyone has any ideas why we get mould at the top of the walls in some rooms.

It's a 1960s bungalow, 4 out of the 6 rooms end up with mould at the top of the walls, when it meets the ceilings.

We used to have a lot more issues, but we've managed to get rid of it in most places. We keep the place well ventilated. It just stubbornly keeps coming back in the 4 rooms that I've included in the pictures. They are all outside walls, 2 bedrooms, kitchen and bathroom (the one with the grey tiles)

Strangely there are no issues in the lounge or the 3rd bedroom at the front of the house.

Any thoughts/ideas?

 

[endecotp]

These are likely the coldest spots on the walls. Any moisture condenses there.

In the loft, does the insulation go right to the edges?

What is the construction of the walls?

What is the typical % relative humidity in the house?

 

[obliquegeek]

The insulation seems to go all the way to the edges, but I'll double check that.

Not sure on the wall construction, brick on the outside, block inside with some cavity insulation. Not sure how to tell what it is.

No idea of the humidity, how would I measure that?

 

[Harry Bloomfield]

No idea of the humidity, how would I measure that?

A humidity meter?

Warm, moist air rises, cold air falls. Which means the coldest walls are near the ceiling, meeting the moist indoor air - will condense out, at the upper corners of the rooms.

Improve the insulation in the affected areas, reduce the moisure, by bathroom extraction, and a cooker hood, avoid drying clothes indoors, especially on radiators.

 

[endecotp]

No idea of the humidity, how would I measure that?

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[noseall]

Hi,

Just wondering if anyone has any ideas why we get mould at the top of the walls in some rooms.

It's a 1960s bungalow, 4 out of the 6 rooms end up with mould at the top of the walls, when it meets the ceilings.

We used to have a lot more issues, but we've managed to get rid of it in most places. We keep the place well ventilated. It just stubbornly keeps coming back in the 4 rooms that I've included in the pictures. They are all outside walls, 2 bedrooms, kitchen and bathroom (the one with the grey tiles)

Strangely there are no issues in the lounge or the 3rd bedroom at the front of the house.

Any thoughts/ideas?

Shaded or NE facing walls will be more vulnerable to say those in the sun. The walls are crying out for insulation and probably an improvement in the loft too.

 

[robinbanks]

The wall-to-ceiling joins are often affected because the wall insulation comes up the cavity then stops, the ceiling insulation rolls out to where the roof slope joins the wall, but gets thinner or stops short to maintain a ventilation path for the loft, and the two lines of insulation (wall and ceiling) may not meet/form a continuous connection. Add in that cold air to ventilate the loft then flows past the area of low/no insulation and you end up with the room top edges being chilled. They then become a passive dehumidifier for house moisture and the damp promotes mould growth.

Your ventilation and moisture generation reducing strategies can only go so far, and sometimes can be counterproductive; leaving windows open long for ventilation in winter may bring internal surfaces down below 14 degrees which makes it much more likely that generated moisture will condense on them

Ensure the insulation layer in the wall meets the ceiling; this is hard, because the design of having such a lack of space at the eaves to effectively insulate and connect the two insulation layers is an inherent flaw that we now design out but that people didn't bother about in the 60s. You may end up doing the best you can with better performing insulation (eg block the eaves up with PIR and install roof vents in place of tiles)

 

[noseall]

No idea of the humidity, how would I measure that?

You don't need to measure it, the glaring (black spot mould) evidence is there.

 

[^woody^]

You need to get air moving, that's what allows mould to grow.

 

[obliquegeek]

Thanks for the replies.

Not sure how we can improve the ventilation much more. Bathroom and cooker are vented outside. Clothes are usually either dried in the condenser tumble tryer or in a drying cupboard that has a dehumidifier in it.

So I guess I'll need to head up into the loft and check for gaps in the insulation at the top of the walls, although it's pretty tight as you get to the edges of the loft. Assuming there is a gap, which seems like the most likely culprit based on what people are saying, how would I go about sorting that and keep the airflow around the edges?

 

[robinbanks]

It would be better to show pictures of the situation in the loft before solutionising.

 

[jj4091]

Couple of thoughts but not sure if they will help. Do you heat the bungalow and if so how. Have you tried painting the affected areas once you have cleaned them. If you haven't try cleaning a recurring patch give it a coat of gloss paint then emulsion over the gloss once it has dried. I'm just thinking that if you have stubborn areas the mould might have become embedded in the plaster.

 

[obliquegeek]

It would be better to show pictures of the situation in the loft before solutionising.

This makes complete sense, just having a little trouble working out how to get to it as the roof angle is narrow and space is tight!

Couple of thoughts but not sure if they will help. Do you heat the bungalow and if so how. Have you tried painting the affected areas once you have cleaned them. If you haven't try cleaning a recurring patch give it a coat of gloss paint then emulsion over the gloss once it has dried. I'm just thinking that if you have stubborn areas the mould might have become embedded in the plaster.

Yes, bungalow is heated when needed, usually an hour or so in the morning and a hour or 2 in the evening during the winter. And yes, it's been cleaned several times with different things, bleach seems to be the most effective and it's been painted over a few times with normal gloss and some stain block paint. Still seems to come back eventually though.