Velux Window wet patches

[catlad]

Velux recommend using their own vapour barrier BBX which fits each window perfectly for this type of installation. what sort of plasterboard was used?
Does one side of the roof get more sun than the other?

 

[Nicola Davis]

We used Gypsum plasterboard and yes one side of house get more sun than the other the side I have the problem doesn’t get a great deal of sun. I’ve just done some more research and funnily enough saw the velux Vapour Barrier - do you think this will help?

 

[catlad]

Assuming the Velux windows are fitted correctly then it seems you have to much heat/vapour escaping and causing problems when the weathers cold.
I always use celotex PL4000 insulated plasterboard which has a built in vapour barrier. Is there a reason the roof wasn't counter batoned? What is the gap left for venting? are there over fascia vents?

 

[catlad]

Did you manage to resolve this issue?

 

[Nicola Davis]

I think we have got to the cause of the problem as around the actual velux rafter framework there is no insulation or vapour barrier so like you said earlier the warm air is condensing with the cold air around the metal within the structure of the velux. As there was no room for a velux collar it has left a gap all around the framework where the velux sits about finger width.

 

[JPat]

We are having exactly the same issue with our brand new windows. They were fine in the Summer, but as soon as it got cold we noticed water ingress into our rooms and condensation within the frames. You said that you thought you'd got to the cause, but have you managed to fix the problem and if so how? Your help would be greatly appreciated.

 

[Nicola Davis]

It’s taken me over a year to get to the source of our problem and after exhausting nearly every avenue with builders and roofers I decided to do my own research into how and why this was happening.

Is your problem exactly the same as ours ie: the pictures I loaded up? If so, you have a cold bridge, basically long story short, is that the warm air from the inside of your building is hitting the cold air around your velux windows, mainly down to lack of insulation and a vapour barrier.

Solution:
After hours and hours of research on the net and speaking to a fantastic windows technician from Velux I have inserted expanding insulation foam tape (similar to the kind of material that you use in your ears to block out noise) - NOT the expanding foam in a can as this will get into the mechanics of the window frame. You can buy it off the internet it’s called Xpanda expanding foam and comes on a reel & expands to different gap sizes depending on the measurement of the gap around the velux window. It is air tight, waterproof, and a noise reducer plus an insulator. I then purchased a velux vapour barrier and installed as per velux’s instructions, and hey presto, it has actually stopped the condensation forming. If you need anymore advice please let me know - good luck and I hope I’ve been of some help.

 

[JPat]

Thank you so much for your advice. Velux did suggest it was condensation but didn't tell us how to go about alleviating the problem. It looks like our nightmare might be finally over. Just a couple of things to clarify. Did you put the Xpanda foam tape around the frame first and then put the vapour barrier on top or vice versa? Was it the BBX vapour barrier that you used? I so appreciate your help with this.

 

[catlad]

Foam insulation first then vapour barrier BBX

 

[Nicola Davis]

I have attached a picture of what I have used. The expanding foam tape inserts into the gap around the window frame where it meets the wood rafter frame - at this point leave to 24 hrs to expand out to whichever width you have chosen. There should be absolutely NO gaps around the frame work. I also used a roofing tape (pictures attached) over the expanding foam to make sure it was absolutely air tight. I then attached the velux BBX Vapour Barrier (video-instructions can be found on Velux website) it’s quite easy to fit. And job done, all ready to be plaster boarded & plastered AGAIN!

 

[Nicola Davis]

Pictures attached

 

[Nicola Davis]

Sorry it won’t let me upload pictures:

The tape we put over the Xpanda expanding foam tape is called Pro Clima Tescon Vana Multi purpose adhesive tape, then Velux BBX vapour barrier.

All the above can be ordered off the net.

Good luck and I hope it sorts out your problem.

 

[JohnD]

Sorry it won’t let me upload pictures

you can insert photos into your reply using copy and paste.

 

[catlad]

I'm guessing they didn't bother fitting the BDX insulation collar either?

 

[Nicola Davis]

No they didn’t unfortunately, as the chippy didn’t leave enough space for the collars. Had they been fitted I’m sure we wouldn’t have had this problem.