Skylight

In my en suite I have a skylight - a velux window.
The en suite has a fan for Shen the shower is on which I think works ok. However it looks as if there is a patch of mould on the inside of the frame. The frame looks untreated - no varnish or anything but I don't know if the damage is caused by water from the inside or outside.
Not really sure what to do here - sand it down, varnish (?), and see what happens over the next year? Or get a man in yo look at it from the outside and try and ascertain where the problem is. Any suggestions?

Thanks

Mould in bathrooms is perfectly normal, they are high humidity areas, very hard to control the moisture levels effectively.

You know doubt have a 4 inch fan, wholly inadequate despite what anyone will tell you, they are a MINIMUM requirement for building regulations, upgrading to a six inch fan will give you three times the volume of extraction (approx 240 cubic metres, as opposed to 80 cubic metres).

The velux windows are treated wood I think, a matt or satin clear coat, if not, quick rub down and treat with a clear exterior polyurethane varnish will do the trick.

Thanks SP1 - nice chap!

[Sid Squid]

Check the screws on the outside of the moveable frame that secure the flashings. If they're loose or not a snug fit in their recesses water damage to the frame is common.

Thanks Sid.
I don't have outside access, nor inside without removing the ceiling I think!

Looking into it a little more, I think the
At water is collecting on the outside in the lip between the frame and glass and gradually seeping into the frame. Not convinced the people who had the work done chose a particularly good company.

Pics?

I'll sand it down but I'm wondering about the bit which is looking bad. It doesn't feel particularly soft to the touch but is there any kind of resin that would stop it from getting worse?

I don't think it's a problem with the installation as the window is pretty much installed as a full unit and the mould is confined to that. If it was a leaky/bad install then the damage would be to the plasterwork. I rekon a good scrub inside & out with a decent fungicide should sort it.

Is there a trickle vent on that window? In a bathroom I'd leave it open all the time.
I have seen these windows leak through the actual glass seal, your pics show it could be that or helping the problem.
Best thing to do IMO, clean it off as much as possible, bleach based products i find work the best on mould.
Get someone to spray a hose (not jet) while you watch from inside, if it's leaking through the window seal, you'll see it straight away, no point in re varnishing it until you've eliminated the issue tbh.

Thanks guys. I think it probably is the seal, so I'll give the hose idea some thought. More difficult than it sounds because of the location (it looks out over the pointed roof of a long garage!).

thanks!