Condensation / mould on bedroom ceiling

[diy_dude]

Hi,
I have a problem in both our bedroom and my sons room. Condensation is forming on the ceiling and black mould is growing. Hopefully this picture will help.

Should I try to insulate the bit highlighted in the picture?
What else can I try? The house is double glazed, but there are no vents built in to the windows. The wife WONT allow the windows to be open all night to let the moisture out. The windows are very wet each morning since it has got cold.

Thanks,

PS If this is the wrong forum, please accept my apologies (and possibly point me in the right direction)

 

[JohnD]

Yes, you should insulate, but you must leave a ventilation space under the felt or tiles. If there is enough headroom you might use insulated plasterboard or something on the inside.

If the house is humid due to:
- Leaving wet washing about the house or over radiators
- not using an extractor fan during and after using bath or shower
then address those.

You might also consider secretly putting ventilation in -
either trickle vents in the window frames, or removing draught strip high up; or making a small hole in the ceiling so that air can escape into the loft (assuming your loft is fairly draughty, and this is not a bathroom or anything, it shouldn't need to be ducted outside). You might be able to do that by removing plaster above or around the light fittings or above a wardrobe.

It might be necessary to look for a new wife.

 

[diy_dude]

If I do insulate:
The gap is not very easy to access. Dont think I could really fit normal glassfibre insulation. Would need something rigid to poke in the hole, any suggestions? How much space must I leave between the top of the insulation and the rafters or roof tiles?

I am very happy with my wife, and would rather see the damp go...

 

[JohnD]

You can buy slabs of expanded polystyrene at the DIY sheds. I have an idea they are in 25mm, 50mm and 100mm thickness. If your house is fairly modern the roof timbers will have quite regular spacing, so you could cut to (a tight-fitting) size with a breadknife and slide the pieces down. If there are gaps in the insulation you will get dark lines on the cold strips of plaster (pattern staining). If you think the insulation might move (e.g. in the wind) then tack it into place.

You must not block the eaves ventilation. Fibreglass has a tendency to slide down and ruck up so is more often responsible for blocking ventilation.

Anything between a 25mm and 50mm gap between the insulation and the felt would do.

 

[diy_dude]

JohnD: Many thanks for the advice. I'll get some expanded polystyrene and try it. Will have to see if it makes a difference.

To clean the mould up, I have been using a cloth with cheapo bleach. It makes the mould go for a while but it comes back. Once I have put the insulation in, what should I paint the ceiling with? I have seen some bathroom / kitchen emulsion which claims to be mould resistant - is it worth it?