Economic ' Heat V Ventilation' to reduce Mold

[john west]

Elderly couple in terraced house built in 1936 with single skimmed walls. (so no insulating air space between an inner and outer wall). So being careful with not wasting heat is important what with the high cost of energy.

They have had mold easily growing on walls behind sofas and rarely moved furniture. So maintaining some air movement and some warmth become necessary to stop mold. Which is not difficult when rooms are regularly used.

But there is one small bedroom on the north facing side which is readily susceptible to mold since it is a very 'rarely' used room.

Generally all upstairs rooms are kept with their doors shut all day as that has been recommended to maintain heat in the house. (Reduces wind blowing through the house carrying away any warmth).

The question in this post is about what is the best way to treat this 'rarely' used little room to Economically reduce Mold.

Is it to leave this bedroom window open very slightly which gives some air flow, but let the room gets quite cold. Or is it to open the radiator slightly whilst keeping the door and window shut? Or leaving the door open to get some of the heat and air from the landing which seems good. But doing that is going to cost in terms of gas bills since this cold room will constant take heat from the upstairs landing and hence the rest of the house. Not increasing the Gas Bill if this can be avoided is largely behind this question. Grateful for any opinions.

[Brian]

They could try a dehumidifier.

Eldest lived in a small rented flat which suffered from some similar problems. A small dehumidifier helped.

[N_Cook]

Would a dehumidifier work? with no ventillation and with regular emptying of the collector. I thought councils demolished housing stock with single-skinned walls about the time Parker-Morris standards came in.

[The Natural Philosopher]

When I rented a cottage like this, the kitchen was mega susceptible and so was the bathroom

I used wipe down paint in the bathroom and cork tiles on the kitchen walls. solved it completely. The wipe down paint got the condensation, but it all ran off and didn't hang around

You used to be able to get 3mm polystyrene foam sheet to use like wall paper. I think they banned it. You can get sheets of similar foam for use as laminated floor underlay.

Stick that up. paper over and paint.

Compared with single brick its a massive insulator.

[Theo]

I'm going to guess that the house in question is rendered or painted on the outside.

Older houses are built with porous materials. That works fine - moisture travels through the walls and is carried away by the wind. As the house is warmer inside there will be a temperature gradient across the wall which will drive through the moisture.

If somebody comes along and slaps some non-porous plaster, paint or insulation, the moisture is now trapped. If it's rendered on the outside the moisture flows into the wall but can't escape, so you now have a damp wall.

So your options are either to waterproof the inside, so there's no flow of moisture into the wall (tricky to get all the spots), or to remove the outside plaster/paint/etc to allow the wall to breathe.

I'd also be inspecting damp proof courses to check if there is anything conducting moisture into the wall. Often somebody has built a patio or something that comes over the DPC. Also check gutters to ensure there's no rainwater coming into contact with the wall at times of heavy rain - many 'rising damp' problems are actually gutter/drainpipe faults.

For a quick improvement, consider all the places where moisture is generated inside. That's usually:

- kitchens

- bathrooms

- clothes drying

Fitting some extractor fans that vent outside (rather then recirculating) can help to exhaust moist air, especially if they come on automatically. For clothes drying, dry outside as much as possible and maybe consider a tumble dryer, perhaps in a garage or some outbuilding that isn't part of the house so that any moisture doesn't leak back in.

It's definitely worth insulating - internal or external insulation sheets are available, as long as you think through where your vapour barrier is. I would use something designed for the job for fire reasons.

Theo

[Brian Gaff (Sofa]

Well, I have a house built three years later and the problem is the same. In reality, there is no way to not pay more if you are heating more air and have more wall area. I have to say I kind of split the difference, only having three storage units running on off peak and an oil filled anytime heater and a fan heater when needed. 1, I noticed a big difference after very thick loft insulation but condensation on walls after double glazing. After cleaning the offending wall, it was coated in polystyrene, and seems to be pretty good, but needed the ventilator to be opened a little. One of those slidy things over an air brick.

If it really does get bitter then I do shut off the currently unused rooms for a few days, but of course when you open them again, they still need to warm up, I don't see any way out of it if you intend to actually keep stuff in them that needs reasonable frost free storage, like electromechanical equipment. I did also notice that some years ago when we had the outside render repaired and one of those spray on coatings put on that this also helped a lot, Hard to define it of course, but I guess any way to stop any damp getting into the brick is a good thing. Luckily being a mid terrace I have only two walls. Brian

[Adrian Caspersz]

<snip>

1932 non-cavity sold brick walls here.

Inside we insulated our cold walls with 40mm Kingspan and plasterboarded over. Same inside bedroom fitted cupboards. Completely got rid of the mould (or moved it out of sight behind the Kingspan), however our old windows now get a lot of condensation in the morning, that I take off using a Karcher vacuum and then leave them slightly open for an hour after the heating has switched off. Think we need new windows.

Some terraced neighbours, have gone for applying external wall insulation. Grants available?

At some point, I should raise/replace the downstairs floorboards and insulate under. Quite a good draft under them. And I did promise myself last year I'd completely redo the loft. However Covid, a water tank replacement and a nesting squirrel family put paid to that dream.

Next year :)

[RJH]

This just *seems* unlikely to me. The moist air has to wick through plaster, paint/wallaper, then 9" of brick before it evaporates . . .

Much easier, therefore, to condense on the cool surface of the internal wall if there's no ventilation?

I've always associated the 'breathing' of older solid walled homes with their inherent draughtiness.

All of that said, I do agree that *some* moisture will find its way though - just not enough to cause the problems the OP's having.

[alan_m]

I keep seeing recommendations about insulating under a floor void but doesn't a decent underlay and carpet (or matting under laminate flooring) perform most of this this function.

[newshound]

Doesn't approach the Q factor of 50 mm of Kingspan.

[Andrew]

I assume you mean 9 inch solid walls, which is not quite the same as 'single skinned' which I would normally take to mean a 4 inch thick wall, i.e one course of brick or block.

[The Natural Philosopher]

OTOH insulation is a matter of diminishing returns, and is rather useless if there are air gaps as well

For choice I'd for sure go for 50mm - make that 150mm - kingspan, but a felt underlay and a carpet is a hellofa lot better than bare floorboards with gaps.

[Andrew]

Brian, the spray-on coating massively reduces the wind-chill effect of cold wind on a wet outside surface where rain has soaked into the brick or render. The effect of latent heat dropping the temperature of the outside skin the wall (and hence creating a stonking cold radiator effect through an uninsulated wall) should not be underestimated.

Andrew

[Andrew]

I found that 30mm Quinntherm was a useful size. Slap one slab against the wall, then fix with horizontal 30mm battens made out of 95mm CLS timber cut into three, so the width of the circular saw blade gives 3 lengths of 30mm timber. Then infill between the battens with more 30mm Quintherm, then affix plasterboard to the battens.

Good way to collect distilled water though for the iron :-)

I suspect that insulating an external solid wall but not dealing with the air movement under a suspended ground floor means the wall insulation is a bit pointless. A good quality 80% wool carpet and underlay is quite a good insulator

[Theo]

I'm not an expert but I think that still works. The outside is exposed to fresh air, so is drier. (unless you have a gutter issue or exposed to driving rain). A dry thing attracts moisture, like a dry sponge. That acts to pump moisture through the material. It doesn't collect on the surface like condensation, it soaks through.

Mould is a surface organism, it won't grow into the brick. If the wall is being dried from the outside, water is less likely to collect on the surface because it can soak through. If you paint it with a non-porous paint then it can't do that.

I think that's right - you do need the air to be changed so you don't get a buildup of very humid air. Old houses had fires which changed the air and didn't have showers (although they did have moisture from cooking).

At the end of the day, if the rooms aren't being kept above the dew point, you either have to raise the air temperature or reduce the humidity. Insulating will help the former, ventilation will help the latter. The moisture pump through the wall will act to equalise the humidity but it does need a temperature gradient across the wall.

Theo

[Adrian Caspersz]

Got a dry wall, so that works for me.

Though on the ground floor on a windy day some floor air is venting up in a smallish gap between the brick wall and the Kingspan. There's an electrical socket mounted in the pasterboard - If I remove it, there is a large draft, which I should sort out.

It's a huge mess to move everything out of rooms and do the work. Need to sort out the loft first, and replace the windows. Depends how crazy fuel bills get.

There is an underlay and carpet. Not very thick though.

[David]

Noting that this is a variant of the oft discussed landlord/tenant issue. The tenant dries clothes on the radiators but keeps all the windows closed because "heating costs". Then complains of the damp.

There is an awful lot of information missing.

There have been a lot of good suggestions in this thread about how to improve insulation and energy efficiency, but we have no idea of the current expenditure on gas for heating, nor the leeway in their budget.

For example, if the problem is only present for 6 months of the year when the central heating is running (generalisation) then costing various options depends very much on the winter gas bill.

An additional £30 a month for 6 months is £180 a year. This would give an idea of which things are cost effective and which aren't. This would, for example, cover the cost of a mid range dehumidifier which is a reasonable suggestion for keeping one small room damp free. If they can't afford £150-200 on a dehumidifier then other options are very limited.

How modern is the gas boiler? Upgrading the boiler could reduce the annual running costs significantly but would presumably need a grant or a loan to cover the up front cost. However the saving on the gas bill would cover heating the small room.

It has already been asked, but where is the damp coming from? Drying clothes on the radiators? Bath/shower? Having an extractor fan in the bathroom which is controlled by a humidistat gets rid of humidity in a controlled manner.

Bottom line is probably how much they can afford. Some people won't heat the house because of the cost even when they can comfortably afford it. Others are on a very limited budget and so are hamstrung when it comes to investing to save money in the medium/long term.

Cheers

Dave R

[Vir Campestris]

Our house is (mostly) a couple of hundred years older than that. Our bedroom is in the new bit; in the winter we run a dehumidifier for a bit in the mornings, and whenever we dry clothes.

The heat of the dehumidifier stays in the house; in fact you get a bit extra from the water it has condensed out.

Andy

[RJH]

Plus of course the running costs - if only 20-30p a day add up. A friend has been trying to persuade me to use my dehumidifier to dry clothes, rather than the tumble dryer. Fair enough of course. Measured using a meter, tumble dryer

2.2kW/h, dehumidifier 1.5kW/h.

So not much in it in terms of economic cost, plus all the faffing about with the dehumidifier. Much rather dry on the line though and do whenever I can.

I realise that you're not saying otherwise, but financial cost isn't the only variable.

There's comfort (slower temperature changes, fewer draughts for example), the health benefits (mental and physical), costs and inconvenience associated with managing the damp, and some degree of relaxation from the thought that you're throwing money away through energy waste. And you might get some money back through various schemes, at the time of sale etc.

Plus the environmental benefits - which I do realise don't get much traction on this NG.

So IMHO it's not a simple spend this-save that equation.

[Theo]

Here's a thought experiment. It's a 'small north-facing room' in a mid-terrace. That means at most one wall is exposed to the outside. How much would it cost to fit some insulation to just the inside of that wall?

For example, here:

can get a 2.4x1.2m sheet of 72.5mm plasterboard-faced PIR for £70. Let's assume that the 'small' room is maybe 2-3m long on the outside wall dimension. That's probably 2-3 sheets, so about £210. (I'd probably buy from somewhere local, but for illustration)

If they were to mount that on the internal wall (using insulated fixings, not metal screws/nails), and seal the gaps, it would raise the internal wall temperature and so reduce condensation on the wall. That might keep the moisture in the air rather than condensing, and it would mean the room took less to heat so they could keep the heating on in there (which is the fundamental issue, assuming they aren't drying clothes inside or having a shower with no ventilation).

It wouldn't do anything for the roof or the floor, but it might help the immediate problem.

One other thing though: there's a mindset thing. Some people have a tendency to scrimp on the heating because that's a bill they can see, which then causes them more costly issues later. They may need training that a certain level of heat is necessary, and not running it enough is counterproductive.

If this is beyond them in terms of money or labour, it's worth looking at the ECO scheme:

may assist. Although I would want to make sure the installer is doing it right - some of them are the 'throw some insulation in the loft' brigade, and I don't know how well they handle trickier problems.

Theo