Why are my Velux loft windows going black?

[con1_uk]

Hello,

I recently cleaned the loft windows and noticed quite a lot of black mould around the wooden frame (once the window was opened) is this normal for roof windows? The wood even when cleaned is still black.

Any ideas why this has happened and how to clean the black of please?

 

[stem]

So was mine, it's mildew caused by condensation from the edge of the glass soaking into the wooden frame.

I sanded the frame down, cleaned it with bleach and then applied several coats of good quality yacht varnish. Then I stopped the condensation by fixing a sheet of perspex over the whole frame, making it triple glazed.

 

[con1_uk]

Thanks for the reply,

Most of my black is on the frame not the window and only visable when you open the window, could this still be condensation?

 

[masona]

Yes I have 6 velux windows and only 2 of them get a slight black mould on the bottom but now I clean it regulary, it's okay now. Already changed 2 of them to upvc velux electric which doesn't get any black moulds