Condensation in loft after new velux windows

[Dave4290]

Earlier this year we had two new loft windows (see link below) installed to replace some very old rusty iron ones that smashed in high winds. I have now noticed condensation building upon on the inside of the glass and wonder what might be the cause and the best/easiest way to remedy this. Here is my scenario:

- No obvious sign of condensation that I know of before new windows installed
- cold water tank in loft but no sign of leakage
- did have a small leak in loft when i accidentally knelt on a pipe whilst looking at said broken windows. This was fixed quickly.
- cant see any gaps or light from outside coming into the loft, but assume being an old house must have some natural draughts and ventilation? The insulation could be blocking any of this
- no visible tile vents
- House built in 1970s and has plenty of insulation up there.
- not sure if the roof is felted inside. All I can see is wooden roof joists and wood on the inside
- house downstairs has poor ventilation, we don't get condensation downstairs (unless we dry clothes inside) but air does smell a little stale. Was hoping to fix this with a loft PIV system, but assume no point doing this until I fix this new problem I have in loft

Here are windows we had installed.
cold room

 

[Dave4290]

Just saw there is a forum specifically for lofts and wondering how I move this post into the other forum?

 

[Mr Chibs]

Is your loft hatch insulated?

Warm air from 'the house' will rise up into roof area, and if it can't get out easily will condense on the colder surfaces.
What have you got in the way of ventilation in the roof?

Were the old skylights single/double glazed?

 

[Dave4290]

@Mr Chibs

Loft hatch is the old fashioned lift out that has insulation taped on loft side

I cant see any obvious ventilation in the roof apart from two tile vents that used to be used for bathroom ventilation, but the bathroom duct has been removed from the tile vent so should be letting some air in.

Old skylights were single glazed

 

[Mr Chibs]

Hello again,

How is the bathroom currently ventilated... is it now extracted through the wall?

What is underneath the roof tiles, black felt, or breathable membrane.

 

[Dave4290]

@Mr Chibs

The bathroom is an ensuite of a bedroom that isn't used at the moment; the only thing used in the bathroom is the toilet. The ceiling ventilation in the bathroom is still there but is not connected to the tile vent so I guess hot air, although not steamy, could be entering the loft through that? This would have been happening before, but if the old window had a gap it was perhaps providing natural ventilation?

Not sure what is under the roof tiles - I can check in the morning