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. 

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?

You're only needing to see what falls out of the hole you don't need to get your arm in. Just stick a bit of wire in and see what you can hook out. But look in the loft first

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?

You're just looking for unevenness of temperature - voids in the insulation basically where it either hasn't been installed properly in the first place or has packed down over time. The issue around the air bricks might be that insulation has been lost/ disturbed  when they were installed and created a cold patch around them.

One thing that can frustrate the whole process  a bit if you do discover theres moisture in the masonry and take actions to solve it - is it takes quite a long time for the walls to dry out once you've taken the source of the damp out of the the equation -  so solving the problem won't necessarily yield instant results and you can be unsure for quite a while whether any action you take has had any effect.

One thing that compounds this is if you use a moisture meter to check the walls (which might be worth your while doing as they'll detect where moisture is present in the fabric even now its warmer and dryer in the house) is that once the damp is solved it can leave salt deposits in the plaster which the meter can also read is damp even though the wall is now dry. So a meter can tell you theres a problem to solve but can't necessarily tell you that you've solved it later. But a meter might be an idea - you can take lots of spot readings and that might highlight where the problem is stemming from.

Keep the air bricks!

Makcruisikeen's advice is spot on.

Are you absolutely certain that there are no structural issues?

Currently I'm very deeply in to trying to get my house dry. New roof, new injected DPC and as we speak new render is going onto all walls. Downstairs was tanked last year as a stopgap knowing that we'd have to do external works soon. The kids inheritance is going to be bricks and mortar and wood and slate. But it will be dry!

Problems we have found in our 1907 sold brick wall house have been water ingress from above due to failed roof, penetrating damp from the cracked render allowing water to be absorbed by the lime mortar, poor guttering, poor drains, failed gulleys... You name it, we've probably had it. 

Lessons learned that helped us cope.

1. Ventilate! 

2. Heat if you can, it makes a huge difference. Wearing warm clothes is fine for you but not so good for the building.

3. Open the kitchen window when the cooking gets steamy.

4. If you have to dry clothes indoors keep your drying in one room, I suggest the bathroom. Open the window, flip the clothes as they are drying. Extractor fans are wonderful and can be found with humidistats. Keep the door closed.

5. Dehumidifiers are brilliant.

6. Burp the house daily.

7. Consider the future. Are you owning or renting? If owning it's worthwhile improving your house to keep it comfortable and to protect your investment.

If renting speak to your landlord.

We are fortunate to have an ISA we can use to cover the price of the works we're having done at the moment. The builders are absolutely fantastic, lovely guys, great workmanship and great value too. If you go down the major works line I really hope that you are as fortunate.

Have you considered getting a surveyor in?

thank you all, really useful advice.

Are you absolutely certain that there are no structural issues?

well no, but id be surprised, its generally in good nick outside.  id be interested in finding out the level of CWI left in the wall tho, and also the moisture content in various positions so i may invest in one of those cameras and a moisture meter.

as for your 7 points above @Ambrose, id say theres only no2 we fall foul of, we pretty much do the rest.  it IS a cold house, and we try to save on the heating bills by sticking another layer on rather than warming the house and watching the tenners floating out the window.  i can see thats not the right thing to do but..... its tough to go against our principles of saving pennies wherever we can.

one thing (well 2 things actually) that went through my analytical mind whilst laying in the bath...... all of the above advice, airbricks, trickle vents, ventilate ventilate ventilate...... so why do 'they' try to get passivhaus status on grand designs, where everythings sealed to the nth degree and ne'er a breeze shall be felt?  no airbricks or trickle vents in those bad boys!

and secondly, i think that condensation happens when warm air meets the cold air or cold surface yes?  so why isnt it worse if theres warm air inside?  why isnt the difference greater, hence making more condensation?  if the air inside was the same temperature as the air outside then theres no difference to form condensation 😀 likewise with cars outside..... the air inside a car is same temperature as outside, so why condensation on the inside on cold mornings?

im sure the answer is, well, science innit, but are we aiming to get a breezy house or a nice warm sealed house?

voodoo i tell ya! 😀 

thanks

one thing (well 2 things actually) that went through my analytical mind whilst laying in the bath...... all of the above advice, airbricks, trickle vents, ventilate ventilate ventilate...... so why do 'they' try to get passivhaus status on grand designs,

Those are houses built to work that way from the outset - a completely different model of construction. They weren't designed with an open fire and chimney.

Some houses need air flow to 'work'

Older, single skin buildings - the mortar (and render) were designed to 'breath' - but in effect that means they need to be breathing 'out' all the time - as in warm dry heat from inside (the open fire)  pushing moisture out of the porous walls. Let them get cold and they breath 'in' instead. People get into bother when they paint old buildings for instance as that prevents that outward push of moisture (big old stone house across the way from us is currently having all the paint sandblasted off to rectify damp problems.) And poor choices of insulation can cause the same problems too

and secondly, i think that condensation happens when warm air meets the cold air or cold surface yes?  so why isnt it worse if theres warm air inside?

Warm air can hold more moisture than cold air - condensation happens when the air is cooled and loses it abilty to carry the moisture.

But warm air need not necessarily also be moisture laden - adding heat doesn't mean adding more moisture

but are we aiming to get a breezy house or a nice warm sealed house?

you are aiming to get a warm AND ventilated house. Ignore the passive houses on grand designs because thats not your house

im sure the answer is, well, science innit, but are we aiming to get a breezy house or a nice warm sealed house?

here are some key points to wrap your noggin around in your next bath

1. living and breathing in a building adds water to the air. the warmer the air the more water it can hold. just existing as a human in a building warms the air. but when the air cools below the due point, the water will HAVE to fall out of the air and you will see it doing that by condensing on a cold surface

2. the heat you put into the house by living in it or heating with rads etc ISNT JUST IN THE AIR - some of it is, but mostly you're heating the fabric of the building. the furniture, the walls, everything inside the "thermal envelope"

3. cold air outside has less water in it because of the science in point 1. 

4. when you burp your house, the warm and damp air leaves and is replaced by cool dry air but heres the kicker - not all the heat energy was in the air that left (point 2 above) so the cool but dry air quickly gets warmed by the heat energy stored in your walls, furniture and everything inside the thermal envelope. 

5. dry air takes less energy to heat than moist air because science 

with all of the above, what youre trying to fine tune is remove damp air so that it deposits its water conveniently outside the house and maintaining airflow so that the cool dry air is warmed by the fabric of the building

if you wanted to see this in action, you could heat your house (as a one off - dont panic) to 22 degrees over a couple of days in winter - get it proper toasty and warm - then open every door and window for 2 minutes and watch the air temp drop to single digits, then close everything up and watch the temp return to 21.8 without any heating on 

dont worry about passivehaus stuff - theyre forcing air through heat recovery systems so that the warm damp air dumps its heat on its way out and the incoming cold air gets the energy in exchange, but thats the final few percent of efficiency that frankly, you dont have the budget for so dont let it concern you 

lovely, really appreciate your answers, its making the voodoo more understandable.

plasterer is coming round for a yap this afternoon.  ill broach the subject of the thermal drylining but looking at my wall i dont think we'll go ahead as itd be a lot of faff with moving/replacing skirting board and coving.  yeah, bit lazy maybe but im thinking because of your (collective your) answers above i understand it a bit more and hopefully can work to an even more efficient warmth/moisture content way of living.

i'll borrow a TIC from work tho to monitor the walls at various times of the year, and also get my hands on one of those snake eye cameras to have a look inside the cavity.  i just took the air brick vent off to have a look, and there is some white dry foamy looking stuff, but i cant be sure its fully insulating the whole wall after so long.

cheers

how much do you think a PIV is ? - you don't have money for a PIV but you do have money for replastering and the like ? 

250quid should see you with a PIV that needs a single 240mm hole cored into your attic and a 240v feed running to it . 

PIV although Crude - does help massively - we ran into this issue when we dealt with a lot of air tightness issues and then got condensation forming on the dormer cheeks which lead to mould. 

We added a PIV 2 years ago now and have had zero issues - allows us to ensure we have sufficient air for the stove also. 

ok i takei t back 250 quid 2 years ago - is now £ 340

how much do you think a PIV is ? - you don't have money for a PIV but you do have money for replastering and the like ? 

hmmm..... looked into this a few years back and the cost put us off.  im seeing prices of over a grand, but thats installed, i assume you mean for me to instal myself?   is it easy?  am i right in thinking a unit in the loft with ducting into the hall and then leave doors open and it 'pushes' air out and replaces with fresh?

would it be effective over the whole house? (4 bed bungalow) and would it counter heating the house, you know, cold air being drawn in when the heatings on?

certainly worth considering as well as replastering the wall, which im expecting my mate to quote around £100.

its slightly the opposite - instead of cold drafts your pushing around warm air at a controlled rate and out the gaps the only place i feel any draft is if i stand on the landing under the outlet.  Yes it'll have a net cooling effect but its less than if you let the cold air come in the drafts of its own free will. 

Think of them as a low speed high volume extractor running in reverse - sucks in attic space air through hepa filters ( reminds me i need to do my yearly clean) keeps the house air much less stagnant  - really notice the difference when you have been away and the house has been closed up for a week or so. uses about 4w/hour - and i have ours on my wiser system to run only at night (quietly and about 4 ft from my head while im in bed) AND/Or if the humidity rises as reported by the wall stat on the wiser system. 

a grand sounds like a MHVR unit that's the next step up - and id have had one if it wasn't for seeing similar costs to you - also much more intrusive to retrofit . i have found the PIV to be a more cost effective unit to install - and much more £friendly than the Dehumidifier i used stop gap. 

https://www.screwfix.com/p/vent-axia-pure-air-home-positive-input-ventilation-240v/939ht

I dont believe they are the best solution to the problem but all things considered i decided they were the most cost effective/bang for buck way to resolve my issue medium term - IF i ever get the notion to sort out the insulation in the Sloped celings ill investigate a multi room MVHR while i have access for the ducts . 

No, it's the PIV that's quoted at around a grand, the MVHR looks around £4000-£10,000. 

Obviously cheaper if I do it myself. 

Edit: just seen your Screwfix link, I'll look into this thanks

Before spending money I'd turn the thermostat down 1° and run the heating constantly. Can still setback or turn  off overnight. You'll probably need to experiment to find the right balance between heat/cost

A house with warm fabric (even at a lower temp) will feel much more pleasant than a house with short bursts of heating. The short bursts only heat the air and leave the fabric cold and damp, rooms will feel draughty too as the warm air moves about. 

By running for long periods you might be able to turn the boiler flow temp down making it more efficient too. 

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.

A plasterer will just agree to do what you ask them too - whether is a good idea or not isn't really up to them