Insulating Oriel window with condensation problem

[Waterworld]

Hello,
Grateful for any help with this. We have this old Oriel window in an 1830s property which has been retrofitted with Iroko double glazed units. It has a triangle shaped block of Kingspan built into the underside and the inside of the projecting platform has also been insulated as it was incredibly drafty.

There are now no drafts at all. However, on colder days, the wood along the bottoms of the window casements are saturated with condensation and prone to mould build-up. The bottoms of the glazed areas do have a touch of condensation but that's to be expected.

What we can't figure out is why the wood would get so cold as to cause such huge quantities of condensation there. The casements have been sealed outside around their edges. The paintwork was freshly re-decorated this past summer. Have we missed something?

Thanks all in anticipation.

 

[blup]

The condensation occurs because there is no ventilation to remove the warm moist air from the house. So it condenses on the nearest cold spot. It is a question of trial and error to get the balance right between insulation and ventilation.

Blup

 

[Waterworld]

Hi Blup,
Many thanks - I suppose my main question was trying to understand why these areas of wood might be so cold as to cause the condensation in the first place. No other room in our house forms condensation on the wooden areas of the windows. The wood is sometimes colder than the glass!

 

[blup]

The glass is thermally more efficient than the wood, which in an exposed position, so colder than other windows. The wall will be uninsulated as it is an 1830's property, there is an adjoining wall that might block sunlight, your wall may be facing north or north easterly, there are all kinds of factors that affect the window.

Blup

 

[Waterworld]

Thanks. Turns out the exterior paintwork is allowing water to soak through.. that's why the wood is so cold to the touch inside.