Velux Repair help

[deema]

First things first, I need to get the sash out and take it apart. Taking the sash iut is very easy, tgere are just two pins either side in the hinge track gullet that you just press in. The sash can then be lifted out of the hinge system.
This is the sash in the bench ready for taking apart.

 

[deema]

The four screws come out to enable the two side caps to be removed.

 

[deema]

The aluminium U shaped frame is then unscrewed. This is held to the glass by butyl sealant.

 

[deema]

The base cap is them unscrewed allowing the glass to simply lift out. It’s not stuck to the frame.

 

[deema]

I can now see the full extent of the rot, and start to cut it out ready for splicing new pieces into it.

 

[deema]

First piece fitted, glued and planed in place. I’ve used PU glue which is good to go in 30 mins

 

[deema]

Second pocket cut ready for splice

 

[deema]

Last two pieces made and glue up underway

 

[deema]

Once the clamps came off, it was just a case of a quick clean up and light sand.

 

[deema]

I’ve reassembled the window and popped it back in. I didn’t have any butyl to seal it with properly, that’s now on order. I’ve ordered 10x2mm butyl, which will I believe be a good fit. I could have just used silicone, but that would make it a pain to take apart in the future. So, apart from taking it out to seal the glass properly and an internal paint it’s done. About 3 hours work. The double glazed unit measures.
628x794mm
15mm thick 3-9-3

 

[rogxwhit]

Tidy work! As an aside since you mentioned silicone, the silicone used for glazing is a low modulus variety and also has a neutral cure. It stays fairly soft - it's anticipated that dg units will fail.

 

[ian33a]

The glazing units will almost always fail, at some stage (unless the never get exposure to sunlight).

With the butyl, if you are really careful, you can remove the glazing units and keep the seal intact. I've managed that many, many, times. Even if it does split slightly, it's seldom an issue.

If replacing the double glazing units, if the units are above a living space, especially in a bedroom, always fit toughened glass. If the units were to catastrophically fail, you wouldn't want shards of glass falling on family members. Generally, I tended to fit toughened on both units.

If the Velux unit is a single one without a similar nearby, fit a Low E pane as the inside pane as it reduces solar gain in summer and keeps energy in during the winter.

Velux panes tend to have a customised thickness of space bar (normally an odd rather than an even sized). You can round up to the nearest even sized mm (so 9mm would become 10mm, as an example). The glass units tend to be 4mm thick as the panes are seldom large enough to require 6mm thick glass.

While you can buy a full replacement kit from Velux for glass changes - with care, you can specify what is needed yourself and save a lot of money.

 

[TomGW]

Good job. I have one that is beginning to show early signs of damp damage in the same lower corner area. When you had it apart was there any clear indication of the source of the damp - from outside or condensation?
Ours was in an unused and unheated, closed attic room, so had plenty of condensation. However, since early 2020 the room has been converted to be my office, so heated and used, with the door open and being ventilated. During this period I haven’t noticed any actual sign of it being damp even through prolonged days of rain, so wondering if it’s just condensation.

 

[ian33a]

Always best to open the night vent on the Velux if it's fitted. Hot air will rise to the highest point and then condense on the coldest surface, typically the glass. Low E panes mitigate the condensation to some degree but a night vent is always best. Having a door open simply distributes the warm air generated by usage to all rooms at that level - best to gently vent it if you can, even if the room feels a little cold as a result.

 

[deema]

The rot initiated from the inside, water was not egressing in from the outside. The only conclusion that makes sense is that the condensation accumulated in the bottom corner.

 

[ian33a]

The rot initiated from the inside, water was not egressing in from the outside. The only conclusion that makes sense is that the condensation accumulated in the bottom corner.

It generally does accumulate there, especially if it can find its way along the glass edge and over the top of the frame but below the glass. I've seen dozens of Velux units with mould and damp in that area of the window. Velux are pretty decent units provided they are reasonably maintained.

 

[TomGW]

The rot initiated from the inside, water was not egressing in from the outside. The only conclusion that makes sense is that the condensation accumulated in the bottom corner.

Thanks for that. I had begun to conclude that. With the room now heated and ventilated (and no condensation) there appears to be no signs of dampness in the stained area of the frame, even during prolonged periods of rainfall.

 

[deema]

Does anyone know a ’value’ source for the foam insulation that sticks onto the ventilation bar? I can buy an official one, but I’d rather find out what it is and buy that (it’s the Tyke in me). Failing a source, could someone with an intact insulation strip measure how think it is? I’m guessing it’s probably 3mm