Please help with this damp patch on my wall

[dazzler9000]

The white soffit board running around the corner , if not sealed will collect lots of condensation overnight and soak the corner wall .

It's sealed. I checked this last year.

 

[JohnD]

Hi John, was that your way of saying it's definitely water leaking in and has nothing to do with humidity or cold walls?

No, it's my way of saying that condensation is water. Humidity is water. Damp is water. Steam is water.

Rain doesn't fall inside your house.

The most common source of condensation, damp and mould is wet washing draped on radiators or racks indoors. You might as well throw buckets of water at the walls.

Another common source is steamy showers and bathrooms. You make all that steam, you need to get it out. Preferably with a powerful extractor fan. And don't let it drift around the house.

There are still people who boil things in the kitchen and don't use an extractor hood.

If you spend all night breathing and perspiring in your bedroom, what happens to the water you produce?

Opening windows is the cheapest way to get the water vapour out.

Way down the list are leaking roofs, windows, gutters, pipes and drains. Still rarer are heated fishtanks.

Some people have a psychological aversion to ventilation.

Some people were brought up in old houses with draughty windows, open fireplaces and bare floorboards, and never needed to consciously provide ventilation, and mistakenly believe it is therefore not necessary.

Very very rarely, you meet people who are accustomed to hot dry countries and do not understand the problem.

 

[dazzler9000]

No, it's my way of saying that condensation is water. Humidity is water. Damp is water. Steam is water.

Rain doesn't fall inside your house.

The most common source of condensation, damp and mould is wet washing draped on radiators or racks indoors. You might as well throw buckets of water at the walls.

Another common source is steamy showers and bathrooms. You make all that steam, you need to get it out. Preferably with a powerful extractor fan. And don't let it drift around the house.

There are still people who boil things in the kitchen and don't use an extractor hood.

If you spend all night breathing and perspiring in your bedroom, what happens to the water you produce?

Opening windows is the cheapest way to get the water vapour out.

Way down the list are leaking roofs, windows, gutters, pipes and drains. Still rarer are heated fishtanks.

Some people have a psychological aversion to ventilation.

Some people were brought up in old houses with draughty windows, open fireplaces and bare floorboards, and never needed to consciously provide ventilation, and mistakenly believe it is therefore not necessary.

Very very rarely, you meet people who are accustomed to hot dry countries and do not understand the problem.

Oh, I see. Yes, I've done a fair amount of research in this area and I do none of the above nowadays (apart from breath), yet I still have high
humidity. I could probably do with opening the windows more rather than first thing in the morning for 10 mins.

I have fairly decent extraction (Manrose MF100T) in the attics for both bathrooms.

I'd love to get MVHR, but I have a few more important things to do first.

 

[JohnD]

There might be an unseen leak under the floor (or buried in concrete), or down a duct or chimney.

If you go away for a few days, close the doors, and on your return look to see which rooms have steamy windows or other signs of damp.

 

[dazzler9000]

I did wonder as our water bill is a touch more than other people I know, but I did the test back in the summer with the meter and there didn't appear to be an issue. That being said, perhaps it's smaller enough not to register on the meter.

 

[JohnD]

Is it the type with a little bubble spinning under a glass window?

 

[cdbe]

Condensation. Going to be a massive issue in the future with people no longer adequately heating their homes. New building regs forcing big trickle vents on all replacement windows now, not just new openings. People from Rochdale will die from hypothermia not mould in future.

I would introduce some local ventilation - I've done this myself to ventilate behind some kitchen cupboards on a solid wall. You need to get 78mm cores (holes) drilled through the top (just below the ceiling) and bottom (just above the skirting) of the solid wall and cover with some soffit vents. This should resolve the issue till you get the wall insulated.

It's not a water leak. The staining pattern would spread from the source, not neatly down the corner, and not in two separate bedrooms, on the first floor.

 

[JohnD]

Condensation can arise from humidity that is caused by a leak, especially in or under a floor.

 

[cdbe]

Condensation can arise from humidity that is caused by a leak, especially in or under a floor.

Of course, and it always climbs up the stairs and across to the corners of the first floor bedrooms.

 

[JohnD]

Of course, and it always climbs up the stairs and across to the corners of the first floor bedrooms.

As you rightly say, any water vapour inside a house diffuses through the air and spreads throughout the house. It is lighter than air so will accumulate upstairs, and can pass through porous materials like ceilings

Much as the smell would if you were frying onions, all day, every day.

Thank you for pointing that out.

 

[cdbe]

I'm not convinced - how long does it take? I've actually had a bag of onions (raw, not fried) under my ground floor for weeks and I can't smell a thing in the corner of my bedroom.

I've got a friend with a high water table and a sump/pump under his floor - he doesn't have damp bedrooms.

 

[JohnD]

Start frying them. All day and every day.

 

[Harry Bloomfield]

Start frying them. All day and every day.

You know your onions!

 

[dazzler9000]

Is it the type with a little bubble spinning under a glass window?

A bit like this.

 

[dazzler9000]

Condensation. Going to be a massive issue in the future with people no longer adequately heating their homes. New building regs forcing big trickle vents on all replacement windows now, not just new openings. People from Rochdale will die from hypothermia not mould in future.

I would introduce some local ventilation - I've done this myself to ventilate behind some kitchen cupboards on a solid wall. You need to get 78mm cores (holes) drilled through the top (just below the ceiling) and bottom (just above the skirting) of the solid wall and cover with some soffit vents. This should resolve the issue till you get the wall insulated.

It's not a water leak. The staining pattern would spread from the source, not neatly down the corner, and not in two separate bedrooms, on the first floor.

Drilling holes through the wall sounds a bit scary! How many would I need? One at the top and one at the bottom?

Do we know why this is happening? Is it to do with cold bridging, where the solid wall is meeting the cavity wall and the temperature difference?

Have to admit to being a little apprehensive about breaching the fabric of the building. Guess if it makes it worse, I can always fill the hole with expanding foam until I sort out the EWI.