Big condensation on Velux windows in loft room.

[Ramona]

I am trying to figure this out for my friend next door. We both live in a 1920s 2 story brick built terrace house. We both have loft conversions and Velux windows.
However she gets terrible condensation problems on hers, both below and above the purlin. It drips down off the window and down the wall.
She has already had one of the panes replaced in a window. It has not helped. She is now considering getting the entire units replaced with new ones.
Before going to all that expense I want to know why its happening.
In my house I have 3 Velux in loft and I get no condensation at all. The only difference in our places really are that mine is open plan so it gets more warmth coming up from the rest of the house. Hers has a door at the bottom of the stairs going up to it. But she says it makes no difference if door is open or closed.
Now, condensation is caused by warm air hitting a cold surface. Both window panes are colder than the surrounding wall, despite being double glazed. Yet mine dont drip.
Tried having top vents closed, and open. Does not seem to matter. Really out of ideas at this point in time and its frustrating.
Anyone else seen something similar?
Thanks.

 

[freddiemercurystwin]

Condensation on windows is typically caused by a lack of ventilation and/or too much moisture in the air, trickle vents should be open not closed. Start here and see what's what: https://www.diynot.com/wiki/Building:Condensation-in-Houses

Comparing one house with another even next doors is a red herring, the differences will be subtle and many, down to different construction methods/materials/standards and different lifestyles.

 

[ronniecabers]

' condensation is caused by warm air hitting a cold surface ' , but what are the humidity levels? how much water borne vapour is in the air in her property compared to yours. A double glazed unit should be colder than a wall, after all the majority are only 28mm thick (being a velux possible only 16mm though ), and most walls are much thicker! There are sealed units that can keep a bit of the warmth in ( modern upvc ) but unless you address the amount of water borne vapour you will still get condensation

 

[Ramona]

Good point, I'll check the humidity in the room, thanks/

 

[Ramona]

Well it looks like many of the rooms in her house are in the region of low to mid 60's humidity, whereas mine are typically high 40s to mid 50. So that is something to consider.

 

[catlad]

If you open your skylight with the large bar at the top it will reveal a data plate, if you post this and your neighbours I will be able to tell you if there is any difference in your skylights.

 

[JohnD]

Do you know where the water is coming from?

Common sources are wet washing draped around the house or hung on radiators

Or steamy showers without a powerful extractor fan.

Water vapour is lighter than air so it rises through the house until it escapes through ventilation

Or, as in your case, finds a cold surface to condense on.

What ventilation does the loft room have permitting it to escape?

 

[Wayners]

We used to get terrible condensation on 3 large bedroom velux windows. Wooden frame has rotted a bit unfortunately. We now dry washing with a dehumidifier and fan and run the dehumidifier every evening in bedroom for 3 hours.
We also run another dehumidifier downstairs for 3 hours in the evening.
Problem solved

 

[Ramona]

If you open your skylight with the large bar at the top it will reveal a data plate, if you post this and your neighbours I will be able to tell you if there is any difference in your skylights.

Thanks, enclosed here. Mine is the newer look

ing one with the QR code on it.

 

[ronniecabers]

Yours will have thicker sealed units ( 24mm ..16mm air gap) and Low e glass( and safety glass ), your neighbours will only have a 16mm thick sealed unit ( 8mm air gap ) , no low e glass and probably not safety glass either as standard. So you've actually got a better insulating velux than your neighbour which is another reason why they will be getting more condensation

 

[Wayners]

I have 3 x 1200mm velux widows. I used to use a window vac every morning to clear the Water before we started using a dehumidifier

 

[Ramona]

Yours will have thicker sealed units ( 24mm ..16mm air gap) and Low e glass( and safety glass ), your neighbours will only have a 16mm thick sealed unit ( 8mm air gap ) , no low e glass and probably not safety glass either as standard. So you've actually got a better insulating velux than your neighbour which is another reason why they will be getting more condensation

Thats very useful info thank you. I cannot find that kind of detail on the Velux site. They do not seem to list the thickness of their glazing as such. Instead its just divided into categories of bestness. Im sure she can take that up with the installers as and when that happens.
I imaging the the bulk of the cost is the frames and fitting rather than the glazing though. If she is going to preplace them it makes senses gettting a significant upgrade.

 

[ronniecabers]

You won't get the thinner units in new veluxs these days , due to minimum u value (energy efficientness ) requirements of windows . You used to be able to get kits to put the thicker sealed units in but the last time I looked they were no longer available

 

[catlad]

Hi Remona
The skylight with the gold data plate was made between 1992-2000
and the silver one is the current generation, so as Ronnie has pointed out the new ones are more efficient.

 

[catlad]

Just looked at the production codes and yours was made in 2015 and your friends 1998