have I created a damp problem?

[diy_fun_uk]

I live in a bungalow and some of the vents in the soffits were perished, allowing wasps etc to enter the loft space and create ENORMOUS nests so earlier this year I decided to cover the vents that were perished. the original vents look like this (this one isn't perished so wasn't covered):





and I covered the perished ones with a metal mesh with largish gaps but small enough to keep wasps etc out:





I appreciate it's not overly pretty but part of the ugliness will be masked when I paint the soffits etc next year. I was careful to ensure all of the original vent space was still visible i.e. not covered by the adhesive I used. so the soffits are now a combo of original (uncovered) vents and covered vents, another view of the latter:



as I say that was earlier this year and I never noticed any issues. however over recent 2-3 months I've been getting black mould on the ceilings in the bedrooms and kitchen. it's appearing at the perimeter of the rooms along the ceiling edge where it meets the wall and it 'looks' as if it's internal/airborne mould cause by internal conditions as oppose to damp from above, however it's only appearing on the sides of the ceilings that have the roof edge/soffit outside. i.e. the ceiling sides that have the walled ends of the property outside are mould free.

this is making me wonder if my additional soffit covers are impeding airflow into the loft space?

I've been in the loft (not to the edges) and it feels cold which I think it's supposed to i.e. in this weather I can see my breath and I definitely feel it airy up there i.e. air moving around. as I say I've not been to the loft extremities but it appears damp free. I've been in the property about 3.5 years and never had issues until last few months, hence me wondering if I've caused it by above actions? I do dry my washing indoors and windows are closed most days due to me being at work.

so, in your opinion, is the damp being caused by internal conditions or have I lessened airflow into the edges of the loft space??

 

[Alastairreid]

Is the insulation in as far as it can go without impeding the airflow from the vents?

I doubt changing the mesh on the vents is going to make any difference to the airflow.

 

[MidsTW]

I highly doubt you are restricting airflow with the mesh!

More than likely that your roof insulation is pushed tight the the eaves preventing the house from breathing.

 

[JGod]

There are a few things, that are commonly misconceived about mould, damp and humidity.

Firstly your mould is guaranteed 99% caused by insufficient ventilation form the two 'wet' zones in your house, if a surveyor says damp - he is an idiot.

You basically need to ventilate them more.

You will find that the same thing will happen in the bedrooms as the weather gets colder, take a cold glass bottle out of the fridge into the bathroom and see what happens (fridge is about 4 degrees C), it will get condensation on it.

You have a ventilated loft and no matter how hard you try, the eves will never have as much insulation as the main body of the loft, the walls will be colder, and are probably closed with slate or similar if you have a cavity - which forms a cold bridge. Added to the fact that the vents generally let air onto the brickwork, which increases the cold spot problem locally, but controlling the internal humidity is key.

The external envelope having a colder surface temperature than the internal walls and as you boil kettles or sprouts, have a shower or bath, or breath out (up to 1 litre of moisture a night apparently dependant on internal temperatures).

You can reduce this quite easily, open the window when you have a shower, even reducing the room temperature by one degree will help as well.

The problem comes (usually) by 'over' draught proofing, retrofit windows and doors that do not allow the building to breath, PVC based emulsion paints that stop walls breathing e.t.c.

The ultimate cure is to use a heat recovery system (or individual units in the Kitchen and Bathroom) to recover wasted heat from the air vented to the outside, and pre heat 'new fresh. air pumped back in - they are very efficient.

Many houses are now 'accidentally' sealed, and as such like a tupperware box, the air needs to change as the house has to 'breath' as you do !

HR systems are very expensive, and don't forget for an extract fan to blow out from the shower, air has to be free to come in to replace it, lots of them sit there and hum but do absolutely nothing.

UPVC windows retrofitted do not need to meet building regs (in general) and as such people almost never ask for the to be fitted with vents and if they do they are always too small if it were a new house.

 

[diy_fun_uk]

thanks all for your replies i'll check the insulation this side of new year to ensure it's not fitted incorrectly and, in a way, i feel better knowing it's very likely being caused by factors below the ceiling as oppose to above it!

 

[JGod]

If it was above (other than a potential lack of insulation), there would be direct staining, rather than surface mould.

Wipe it with a solution of 1/2 and 1/2 white wine vinegar, and water with a dash of detergent, to clean, and don't rinse off, the acid will slow the fungal growth. (On a new kitchen cloth).

If you can't sort the ventilation, then do what the previous owner did, and flog the house in the summer !

Avoid drying washing inside - all the water goes somewhere, and that includes the towels on radiators, mop the floor after showers - reduce as much as you can, move the kettle to near the hob extract and turn it on when the kettle boils - as much as you can do to reduce water vapour and the dew point problem that you have that will worsen as the weather gets colder. Its the interstitial condensation (sub surface) that you can't see that is impossible to shift in the winter, and build up in the autumn, as windows are left shut more. It can cause rot, and fungal growth in voids you can't see.