High humidity and condensation

David_Aldred

A number of interesting posts so if you would like further comments are as follows:
To post by iphone: You know the room temperatures but you need to measure the surface temps as well. At 91%RH and a room temp of 12 deg C the dew point is around 10 deg C so anything be that walls or windows at or below 10 deg C will have condensation form upon it. As I said before you are living in a saturated environment at 91%RH and I mean wet wet.

When a couple sleep at night they evaporate off (no jokes) around a litre of water that goes into the air as vapour. You said in your last post there is no heating on when you are asleep. Please see my last post in that if you let the air temp go cold with no heating fabric of the room will go cold and the dew point will drop too. Repeat of previous comment you need a programmable boiler thermostat that trips in and out to maintain a min temp of something like say 15 deg C but this will only be of any use if you can get the relative humidity down to under 70%RH such that you stop mould flourishing.

Let me illustrate a point - I was asked to inspect a period property hotel room with solid walls that guests were complaining was musty / damp and full of mould. The room consisted of bedroom and an en-suite to the bedroom. The en-suite had a fan linked to the light that stopped as soon as the light was switched off. There was certainly a musty smell and mould upon curtains / soft furnishings including carpet / chairs etc. There was an opening window to the bedroom and an electric fan heater manually operated with no other heating. The relative humidity in the room was only around 55%RH at 18 deg C so the dew point was 9 deg C at time of visit. The wall surface temp was 11 deg C so was above the dew point and condensation was not occurring. There was a manually operated fan in the en-suite and the shower was a fancy level access walk in shower with tiled walls / floors.

When I turned the shower and extractor fan on for 2 minutes the relative humidity rose to 92%RH and this spilled out into the bedroom with the door to the en-suite open. Remember we are still at 18 deg C room temp but now the dew point has changed with this shift in relative humidity to 17 deg C but the wall surface temp remained the same at 11 deg C.

So now the surfaces are well below the dew point and condensation is suddenly running down the wall next to the bed and I can write my name on the mirror in the bedroom even with the en-suite fan going full belt. It doesn't take a genius to realise that some people won't operate the light to activate the fan to the en-suite during the daylight hours and most guests will chat to each other as one showers with the door to the en-suite open. To compound things there is no heating other than the on / off electric heater fan and most people will not sleep with an electric heater fan whizzing away all night.

Recommendations : self closer on en-suite door, change the manually operated 100mm diameter 15 / litre per second extractor fan within the en-suite to a 150mm diameter 60 litre / second humidistat controlled fan that activates automatically at a humidity level below 70% and overruns for 15 minutes once activated and provide warm air heater on programmable thermostat that tripped in and out to warm the fabric of the room up to a min 15deg C or above. Clean down mould with anti-fungicidal products and improve controllable background ventilation. Result relative humidty dropped to normal levels when using en-suite and overnight - condensation within bedroom stopped, mould growth eradicated, clean bedding / soft furnishings and happy guests.

To previous post by converse: Typical specification for modern windows to habitable rooms to be min 10% of combined floor area & opening lights therein to be 5%. All glazing including that to doors to be double glazed & BS Kite marked Toughened Safety Glass between finished floor level & 800mm above that level in walls. Double glazed panes of Pilkington Low E coated glass with 16mm Argon filled gap between panes & units achieving 1.8W/m2.K ‘U’ value. Yes there is equipment you can get to test for low E glass and your local Building Control Officer can sometimes test for you. However in all honesty I think it would be better to play about with loweing the relative humidity and altering air / surface temperatures than paying to upgrade your windows.

To previous post by myhooose: Condensation will hit the coldest surfaces first within the roof void which is usually the underside of the roof covering then wet the adjacent timbers. If the roof has felt beneath the slate / tile battens then if of a non breathable type you can often see droplets form there. Even with good ventilation this will sometimes occur but the key is to provide enough ventilation so as to make this a transient rather than constant occurrence in cold wet weather. Do not pack the insulation into the eaves - maintain min 50mm air gap here. By the way I admit to not being a fan of spraying insulation onto the underside of roof battens / slates / tiles at least in the area I live which is classed as severe exposure as it tends to reduce ventilation to roofing battens / rafters such that they stay wetter for longer and rot the roof timbers. It also means if you ever want to re-roof or undertake a repair the existing slates / tiles have to be thrown away instead of being able to be re-used.

Hope this helps David Aldred Independent dampness and timber surveyor

myhooose

Hi David,

Thanks for your reply. I have not long owned the house and have had the felt and clay tiles replaced with a breathable membrane and Marley tiles. I added 200 mm of loft insulation. Now some of the rafters are damp and there are damp patches where the rafters meet the purlins. Initially I thought it was a leak but now suspect condensation due to the multiple locations of damp. My loft hatch is the size of half a door and directly outside the bathroom door.

I'm going to seal around the loft hatch, remove the insulation from around the eves and increase the bathroom extractor timer overrun to 20 mins and then monitor to see if the rafters dry. However if this doesn't work what would you recommend to increase the ventilation. due to the design of the house I can't access/see any of the eves from inside the loft.

Esqui

Mind if I also hi-jack the thread? Thanks.

I've been noticing recently when in bed that the ceiling seems to be covered in condensation. This morning, I took a closer look and the wall looks and feels damp. But what's interesting is that it seems to be spreading from the top of the wall - there's almost a semi-circle of dampness from the join of the wall and ceiling. We keep the room well ventilated, as it often feels dry without the window open (not nice when asleep).

As I don't have a clue with any of this, does this sound like normal condensation? Or something worse? I may have a word with the lady who lives upstairs from us to see if she's noticed anything.

ariba10

Warm air holds a lot of water. Cold air cannot hold water.

That is why we have rain. Moisture is picked up by warm air and as it cools it falls out as rain.

If you have moist air in your house it will come out on colder surfaces.

You can either keep all the surfaces in the house warm so that the moisture will not come out.

Cool the air so that it will not pick up the moisture.

Or better still stop the moisture at its source.

mariat

Seems a lot of people are having damp/condensation problems, us too. It's a long story, but I'm really hoping someone can help.
About 3 years ago we replaced our old windows with double glazing, and also had the loft insulated (under the governments Warm Front scheme). The insulation installers replaced some of the old pantiles with special vents to deal with any condensation in the roof space. Now, for the last couple of years we have had problems with general damp throughout the house. My leather armchairs in the living room keep getting mold on them, the spare bedroom has lots of mold patches on the walls and ceiling, and the clothes in my sons built in wardrobe always smell of damp. Now, all these rooms are at one of the gable ends of the house, which is built of chalk lump and about 200 years old. I just couldn't think where all the water was coming from to cause all these problems, and we regularly open windows when cooking, having a shower etc. Well, I think we have just found the answer. My OH has been painting the sitting room this week, and to my horror the paint in the alcoves on each side of the fireplace refuses to dry. And this is this gable end wall. But the damp is on the top half of the wall, the bottom half looks dry. I am thinking this may be because the damp course was re-injected when we bought the house, and the walls were re-rendered/plastered up to a height of 1m, and maybe they used waterproof cement, so the damp can't come through there. The damp wardrobe is directly above one of these alcoves.
So, would it be a good idea to hack off the render/plaster in these alcoves to help the chalk wall behind dry out? I know we need to sort out where all this water is getting in, and I am dreading it being the roof. My OH is out of work and I am disabled, and we just don't have the money for such a big repair job. Sorry if I've hijacked the thread.
E2A: The RH is 64%

dampdaveski

ariba, mariat,
sounds like you have bad condensation problems, look on David Aldreds post and mine, your answers are there.
Mariat you are probably correct about the 'waterproof' render , not an expression I would use and I'm sure David will post a 700 word dissitation on the correct expresion to use
You need to check you havn't got defectiver gutters / roof etc, but if you control the condensation you will hopefully remove the need to start hacking the house to bits.

blueberrypie

powerRIP wrote: »

Keep an eye on this and when you see it is low, open all your windows for a while. Ideally early morning before your heating comes on. Half an hour or so of open windows when the outside humidity is low will reduce your inside humidity for several days

What would you call "low" outside humidity?

David_Aldred

Hi Esqui,
I know it is hard to explain a problem you are having but could you explain the layout of your property in the area of the problem or post some photographs showing the problem and the outside elevation perhaps? Is there a room of another flat directly above the problem area and if so what room is this? Is yours a ground floor flat all on one level and what is the construction of the ceiling and outside walls if you are able to determine plus how old is the property as a whole? Kindest regards, David Aldred

David_Aldred

Hi Mariat & dampdaveski,
I agree with dampdaveski, Mariat in that the primary thing that is probably bothering you is the mould issues of which it may be worth you reading some of the previous posts on the forum regarding dampness / condenstion. However there are so many issues that you touch upon within your post I don't want to confuse you with listing a lot of points that could be contributory especially as your funds are limited so the works that you do fund to be undertaken need to be targeted at the primary areas of concern first. Preferably somebody needs to look at what is going on and perhaps with you mentioning that you are disabled it may be worth you approaching Care & Repair if there is a branch in your area to assist with funding and technical inspection if they have somebody suitably qualified at least for an initial site inspection. As indicated above photographs do tend to help an awful lot as an aid to diagnosis and any that you could post showing both internal and external issues of concern would be most welcome for comment. Kindest regards, David Aldred independent dampness and timber surveyor.

2Sheds

What I can never understand with condensation is why we get it and the neighbours don't get a drop?!
We'd have the bedroom windows totally soaked from top to bottom, neighbours either side nothing whatsoever!

Did plenty of research and as dampdaveski has mentioned a few times, we installed a Drimaster, well worth the money. The pro's out weight the con's

but why did we suffer (until the drimaster) with condensation and the neighbours don't