First floor air bricks – damp. Fully seal or open up

Hello Everyone,
I live in a 1950’s semi with cavity walls. We had the cavity filled when we moved in a decade ago.

In two bedrooms and the bathroom on the first floor at ceiling height are a set of air bricks on the external walls. Internally the previous owner plastered over gap.

We are starting to redecorate both rooms and found lots of damp and mould( it was hidden by furniture and wall paper).

The chimney Brest is in another room.

I want the damp to stop. Do I open up the vents, or seal up the exterior air bricks?

You open up the vents. The lack of airflow is what is causing your damp and mould problem.

You may have to improve ventilation/lower humidity in other ways, but opening up the existing ventilation is a good first step.

I have a similar situation where an air brick in my cloakroom toilet has been plastered over, no idea why.

Thanks MH
With opening the vents, is there a way to shut the to keep the noice out and heat in?

Or is this the choice. No damp but cold and noisy or warm and quiet, but damp and mould creeping everywhere?

The previous owner did a lot of unthought diy. We are very slowly undoing it all

Block the vents with insulation/remove them in such a fashion that they can’t be used again and then install loft based positive pressure ventilation.

Much better for your overall humidity control.

The problem with loft based piv is that warm damp air rises into the loft and then gets blown back into the house, along with all the insulation fibres. Don’t put large items of furniture on outside cold walls, extract damp from kitchens and bathrooms at source. Damp in chimney is likely to be hydroscopic salts. You need to keep all rooms well ventilated.

The problem with loft based piv is that warm damp air rises into the loft and then gets blown back into the house, along with all the insulation fibres.

This is patently not the case. Mine has large filters on the intakes and I’m not living in a permanent shower of glass fibre every time I go up the stairs.

With opening the vents, is there a way to shut the to keep the noice out and heat in?

Not really, no. It’s the way the house was designed. You can probably get away with blocking them if there are other sources of ventilation, but a lot of the passive airflow has probably been blocked by homeowners – upvc windows/doors etc.

Remember that damp air is harder to heat than dry air.

PPV does work pretty well, at a cost, obviously.

@scienceofficer why would you choose to have your air supply from an area with glass fibres in, regardless of how well you think a filter works. Warm damp air clearly rises, and this is then forced back into your house to condense on any cold spots. I don’t really understand why you wouldn’t just extract damp air at source with a humidity controlled extract.

Air from your house shouldn’t be getting in to the loft; that will cause a cold house and damp problems in your loft, so PPV not working very well in those circumstances isn’t the biggest problem there.

If air from the house isn’t getting in to the loft then PPV can work well as the loft air will be warmer than the outside air, so you are recovering some of the heat that would otherwise be lost.

If there’s nothing disturbing the loft air then it won’t be full of dust, and the filters on such systems are more than capable of removing anything that does get kicked up.

That’s not really how it works. Water vapour in gaseous form passes through the ceiling fabric into the loft. A large amount of air also passes into the loft through gaps in the building fabric. A door blower air test demonstrates that pretty clearly in pretty much every building type. The insulation in the loft will be disturbed by the required ventilation into the roof space from eaves/ridge.

@ajc it’s like you dont even understand how a filter works.

It’s like I just wouldn’t trust a filter to be changed regularly and wouldn’t want to risk having damp air from the loft in my house when there is perfectly clean air outside that could be used instead. Constant extract or humidity controlled is generally reckoned to be a better option than piv. Better still to have Mvhr in an airtight passive house which is what I have.

The moisture laden air forced out through gaps in the building fabric by piv can also cause problems as it will condense when it reaches the dew point within the building fabric.

That’s not really how it works. Water vapour in gaseous form passes through the ceiling fabric into the loft.

This depends entirely on the construction of the building. Its not faintly black and white like you’re portraying.

Tbh I’m Not sure its worth debating the details. You seem more interested in proving to everyone that your little bit of knowledge is correct, rather than discussing the issue.

For example

It’s like I just wouldn’t trust a filter to be changed regularly

You think filters fail by admitting particles through that are bigger than their pore size?

I really dont know where to begin with that without sounding even more patronising than I already do.

Better still to have Mvhr in an airtight passive house which is what I have.

For sure, but I doubt your typical 1950s build will be faintly near the air tightness standards for viability without a retrofit. What about YOUR filters in your MHVR?

If you want to fit a piv then fill your boots. There are risks associated with it and imo there are far better alternatives. It is a matter of fact that warm moisture laden air if it is present will rise into the roof space of almost any house either through the fabric or through gaps into the loft space. Pushing moist air out through the building fabric is a really bad idea. I am well aware how air tight houses are having undertaken plenty of air pressure and thermal imaging tests during low energy retrofits. I am also very aware how often simple tasks like filter changing get ignored, especially if you have to go into the loft to do it.