Condensation experts - airbrick advice please

I wouldn’t trust chat gpt unless it’s definitely relating to uk conditions with a cavity brick built house!

 If there is mould on the inside near the air bricks I think that would suggest there is still a high humidity issue in the house, the cold air near the air bricks will be encouraging condensation on the wall near it. 

Is it a solid concrete floor or suspended timber, and have you got a humidity sensor (our room stat for the boiler has one). Our house is generally more humid than ideal and we run a dehumidifier quite a bit, and always when drying any clothes indoors.

With condensation that bad I'd be taking a long, hard look for the cause(s). Do you have and use extract fans in the kitchen and bathroom? Drying clothes indoors? Unvented tumble dryer? Keeping the structure adequately warm in winter? Ensuring sufficient ventilation? Any chance of a pipe leak under the ground floor? Is there a membrane under the ground floor? Ventilation under the ground floor if it's suspended? I'll stop there..... 🤔 

I wouldn’t trust chat gpt unless it’s definitely relating to uk conditions with a cavity brick built house!

uk yes, didnt mention cavity wall.

Is it a solid concrete floor or suspended timber, and have you got a humidity sensor (our room stat for the boiler has one). Our house is generally more humid than ideal and we run a dehumidifier quite a bit, and always when drying any clothes indoors.

its a concrete floor and ive just moved the sensor into the bedroom to check, its usually kept in the lounge.

Do you have and use extract fans in the kitchen and bathroom? Drying clothes indoors? Unvented tumble dryer? Keeping the structure adequately warm in winter? Ensuring sufficient ventilation? Any chance of a pipe leak under the ground floor? Is there a membrane under the ground floor? Ventilation under the ground floor if it's suspended? I'll stop there.....

asked about fans on here back in the day and we now have a monster extractor fan in the bathroom, kitchen has a bit of a sh1te one.  we dry clothes other end of the house in the spare room but always with a dehumidifier on and close the door.  no tumble drier, the washings either outside or dehumidified.

we do our best with ventilation, certainly better than we used to be.  itll be a lot easier these coming summer months, its probably winter when we struggle a bit.  concrete floor, no pipes underneath and pretty sure the builder said we've got a membrane.

the one thing we maybe fail on is keeping the house warm in winter.  we try to only put the heating on if absolutely necessary for cost reasons.

i should say, the condensation is nowhere near as bad as it used to be, the floor is always dry now and the mould has probably accumulated slowly over many years.  we had it over the bathroom window too so ive just cleaned that and put some zinsser anti mould stuff on.  again, it baffled me why the mould would be over a window that we regularly open rather than a distant dark corner maybe, its voodoo to me 😀

so im thinking painted plaster with a durable wipeable paint that we can keep on top of will top trump painted lining paper where it might start slowly growing again.  im just not sure whether 2 airbricks that can gather mould (although easily wipeable if kept on top of) is better than no airbricks and rely on trickle vents and a regularly opened window.

thanks

As spooky said, likely to be cold around the air bricks, and you may have a lintel over the window causing a cold bridge, so condensation is more likely there. Best solution probably to thermally dryline the external wall, but a bit expensive and disruptive unless you can diy. Your winter heating regime won't be helping, but otherwise sounds like you're doing all you reasonably can. Hopefully some of the mould is historic and an impervious wipeable paint will make it easier to keep it under control. Good luck!

I’ve usually taken the opinion that only turning the heating on when needed is the cheapest, but I’ve since realised that the thinking is that a modulating, condensing boiler gently ticking over for several hours at maximum efficiency could be cheaper than running the boiler at maximum output (inefficient) for a couple of hours each evening. I’ve not put much effort into researching this but it might be worth looking into whether it might be better allow the boiler to maintain a minimum temp of say 17 degrees 24/7 during the winter.

We have an old end terrace house with single skin walls. It suffered bad mould and condensation until we fitted some passive anti condensation vents and installed a couple of tubular low wattage heaters in the wardrobes. I don't know if it's the placebo effect but the tenants seem to be happy with it.

Downstairs we had some wet plaster hacked off, a membrane applied and a new coat of internal render.  I think old plaster, once soaked, is hygroscopic and encourages damp.

How old is the house?

How old is the house?

built in 1962.

I’ve not put much effort into researching this but it might be worth looking into whether it might be better allow the boiler to maintain a minimum temp of say 17 degrees 24/7 during the winter.

ive looked into it, my 'research' suggests 10-15% higher bills if i keep it ticking over.

Best solution probably to thermally dryline the external wall, but a bit expensive and disruptive unless you can diy.

plasterer is coming round this week so i'll discuss this with him.

if its of any interest the humidity is reading 58% at the moment, although i think thats probably quite low due to it being a nice day, doors and windows open.....

thank you

I have a 60s detached bungalow with damp on North facing walls.  Builders currently putting in a stud wall with insulation between battens.

Cheap solution would be run a dehumidifier in there.

so bad that pulling up the carpet and standing on the underlay left wet footprints.

The floor seems a bit of an odd place for moisture in the air to condense (I've had it happen on a first floor concrete floor that was over an archway so cold becuase it was exposed to the elements underneath but not really on the ground floor). Condensation forms on the coldest surface in the room and I wound't really expect a carpeted floor to be colder that the windows etc.  Ventilation will help clear moisture created within the house (washing/cooking/breathing) but I'd be looking at whether moisture is getting in from outside at floor level

First thing would be to make sure the soil level outside hasn't built up above the level of the damp course (or patios, steps etc havement been added that are higher than the DPC

You mentioned it a cavity wall - is it insulated? If so with what?

This time last year we had our insulation sucked out and replaced - it had previously been the sort of fluffy snow-like fibre and was replaced with resin bound poly beads. The bottom foot or so of the old insulation was sodden and the fibre stuff is notorious for this - behaves like a sponge. But also there was a lot of mortar dust and crud that had accumulated at the bottom of the cavities over time and was bridging the cavity above the DPC.  So between the old insulation being removed and the new stuff install I took a few bricks out and scraped / hoovered all the crap out of the bottom of the cavities.

We mostly have suspended floors - but at in the areas around the front and back doors its concrete and there we we having problems with damp at the bottoms of the walls and cleaning out the cavities seems to have solved this and dropped the typical humidity in the house from 70% to 50%

The floor seems a bit of an odd place for moisture in the air to condense (I've had it happen on a first floor concrete floor that was over an archway so cold becuase it was exposed to the elements underneath but not really on the ground floor).

i hadnt actually considered that, i just assumed moisture in the air slowly lowers (heavier than air) and settles on the floor.  and the builder didnt seem too surprised by it when he saw it.

First thing would be to make sure the soil level outside hasn't built up above the level of the damp course (or patios, steps etc havement been added that are higher than the DPC

nope, no build up, and like i say, the carpets been fine since we discovered it and started positively trying to deal with it, before we'd just not given condensation a second thought.

You mentioned it a cavity wall - is it insulated? If so with what?

pretty sure it is.  its the house i grew up in and i think i remember as a kid seeing cavity wall insulation poured in through small holes in the brick wall.  thatd be in the 60s or early 70s i guess?  is there any way of checking what it is and how effective it is 50 years or so later?

bedroom was 57% moisture when we went to bed and just checked and its the same this morning which is a positive i guess.  or a negative if you consider there was no steamy action last night 😁

is there any way of checking what it is and how effective it is 50 years or so later?

Sometimes you can see from the loft - peal back any loft insulation at the tops of the wall and see if theres any polystyrene balls or white fluff as the material is blown in so tends to spill out of the tops of the cavities. Or - just drill a hole in the wall somewhere unobtrusive (understairs cupboard if its on an external wall - behind the fridge or whatever if you do it inside, or on the mortar line if outdoors so it can be patched neatly) and see what in there.

You could also investigate around anything that passes through the wall - pipes, vents, extractors etc. 

I bought a cheap endoscope that plugs into my phone so I could peek about inside the walls when we had our insulation removed

If you try and do it quite low on the wall you can find out both what the stuff is and whether its wet.

I think an issue for a lot of houses that had things like cavity wall insulation added back in the day is it was part of a range of actions that interfered with the dynamics of the building as it was designed to work. Buildings were built to breath - in through air bricks, out through the chimneys. In the 60s/70s/80s 'drafts' were demonised - chimneys blocked or removed, air bricks blocked and so on and all that prevents the house from working in the way it was designed to

When we had our house re-insulated (1950s ex-council) the insulation work was paired with ventilation - so we now have always on trickle fans in the kitchen and bathroom (which are on humidistat's so boost when theres moisture detected). Originally the house had vents above all the internal doors - so there was airflow between the rooms as will as between the inside and outside - which are all gone now. So we now have a vent in the bathroom door so the fans are pulling air through the house even when the door is closed and we generally keep the internal doors open during the day.

Surprised it took so long for someone to suggest a dehumidifier, so I'll second that. Obviously you want to find the solution if there's a proper damp problem, but in the meantime, treat the symptoms, and in the long run, it's a good thing to have anyway because you'll always have some moisture, unless you stop breathing indoors.

Like you, we try and minimise heating in the winter for cost reasons, and since we're still (relatively) young, we don't mind it being on the cool side, and most days we're both out at work. If you choose the right one (do a bit of research) dehumidifiers are very cheap to run, and dry air takes less energy to heat (not to mention making you feel less cold).

no tumble drier, the washings either outside or dehumidified.

We don't tumble dry but whatever washing cycle I always give the washing one or two extra spins. Seems to make a significant difference to how fast stuff dries (and therefore how much moisture is being released into the house

For some reason I was assuming your house was older with solid walls. I would definitely follow maccruiskeen's advice. You could hire/buy a thermal imaging camera to check out the thermal performance of your external walls.

I don't really see why you'd block up the airbricks that helped you get over the worse of the issue? I wouldn't be concerned with the mould on the wallpaper as its probably a hangover from the damp times and around the airbrick was covered by another reply.

I'd just make sure when the plaster comes all the mouldy wall paper is nuked from orbit and the area properly treated before plastered over

Have you looked into a PIV system?
We get a bit of condensation and I have looked into these over the years. I don't think our problem is bad enough to justify one and my Wife doesn't seem very keen so it is something I have avoided. But maybe worth investigating?

Over the years there have been several threads about them on here and a lot of people think they massively help reduce condensation.

Or - just drill a hole in the wall somewhere unobtrusive (understairs cupboard if its on an external wall - behind the fridge or whatever if you do it inside, or on the mortar line if outdoors so it can be patched neatly) and see what in there.

i assume itd need to be a fairly decent sized hole to see the contents of the cavity, 10mm or so wouldnt cut it?

I bought a cheap endoscope that plugs into my phone so I could peek about inside the walls when we had our insulation removed

they do indeed appear to be cheap, good idea, thanks.

Surprised it took so long for someone to suggest a dehumidifier, so I'll second that.

we have one, a good one that was recommended on here.

You could hire/buy a thermal imaging camera to check out the thermal performance of your external walls.

i can borrow a TIC from work, but what am i actually looking for?  what temperatures?

I don't really see why you'd block up the airbricks that helped you get over the worse of the issue?

yeah im leaning that way now, i was just curious as to whether the mould they attract was opposing the benefit of the air they were bringing in.

Have you looked into a PIV system?

yep, i think theyd be gold standard but just cant afford somethings like that.

thanks for all the advice, much appreciated.

so youve got plenty good advice up there. 

The reason you're seeing mould on the vent is that the vent is the coldest part of the room so thats where airborne moisture is condensing and thats to be expected. 

This time of year isn't great for fault finding because the problem is going to naturally go away anyway but for now you can fix the old mould by spraying your choice of chemicals on to nuke it from orbit. Bleach, Milton, Vinegar or something branded if youre fancy. then paint over it. 

in the autumn, id be using the dehumidifier you have and a logging humidity sensor to see if you can work out whats going on. we use ours similar to you - I put clothes on a couple of airers in my study and run it with the door closed. it will fill its bucket overnight but once the clothes are dry, it won't extract any more - if yours keeps on sucking water, then its coming from somewhere. if you suspect the wall its self is wet, look for causes of that - blocked gutters causing the outside wall to be wet? breached DPC etc. if you suspect a leaking pipe then id be digging a hole now and seeing if it remains wet over august

I absolutely wouldn't be considering blocking an air brick

I'd also consider if a 10% increase in heating bills might actually be a small price to pay to keep things dry. keep in mind that damp air is costly to heat.