DIY Doctor

Is my Velux leaking or is it condensation?

Postby py9mrg » Sun Dec 27, 2020 8:49 pm

Hello,

Today I noticed what appears to be a leak in the bottom left of my velux window. It appears to be a damp patch, but it’s barely noticeable that it’s damp to the touch. It’s not wet wet or anything. We did have a lot of rain last night, but I have a vague recollection of seeing something smaller months ago and dismissing it as poor / discoloured paint (long story). My point being I’m not 100 % convinced this happened “overnight” during the rain as opposed to being a slow / progressive issue.

Some background:

The velux is only 2 years old and is the polycarbonate coated type. It’s in an en-suite bathroom associated with a converted loft bedroom. There is a toilet, sink and (never used) shower in the bathroom. In the bedroom there are another 3 velux windows (normal not polycarbonate coated).

In winter all 4 velux windows gather a fair bit of condensation on the inside of the glass, but usually dry by the end of the day if I don’t remember to wipe them down first. The polycarbonate window also seems to gather quite a lot of condensation on the grey seal(s) and inside of the frame. Not enough to be seen when the window is closed unless you look up into the gap between the frame and window - it’s only really noticeable when you open the window to check, but then there’s a fair amount of loose water that can be seen. That said, I’ve never noticed it actually dripping down the frame to the painted wall below (where the damp patch appears to be).

The normal velux windows in the bedroom never show this level of condensation on the frame, perhaps due to a slightly higher temp in the bedroom part or maybe the polycarbonate coating has a tendency to build up more condensation.

I’ve done some googling and it seems this sort of problem could be a proper leak, or condensation. I’ve had a look at the flashing outside the windows and can see no problems - no gaps/holes or debris/moss build up. The tiles around the window (concrete overlapping type) all seem sound and secure - and the foam the installer put under them is still in place.

Except there is one potential problem tile. When looking out the window and up the roof, it is 2 up from the velux (ie one overlapping the tiles that would have had to be removed during installation). It’s on the same side as the damp patch. These are the concrete overlapping tiles that overlap adjacent tiles with a top and bottom “lip” overlap and their side edges - as well as overlapping each tile above and below. I hope that’s clear as I don’t know the proper terms, sorry.

The only problem I can see is that the end 1-2 inches of the under “lip” (where adjacent tiles overlap) is missing from one of the tiles. I mean that the top part of the tile on the left is perfectly fine and aligned, but where the tile on the right would have the lip part that goes under the left tile is missing a short segment at the bottom.

As far as I can see the missing part is not long enough to mean that there is any missing “lip” far enough up to the tile so that the missing segment goes far enough up to reach the overlapping tile above it. And even in the rain I can see a clear dry few mm around the edge of the missing segment - so it seems there’s no way for water to ingress and it’s an unimportant chip. Could have been there 30 years for all I know (and I can’t see how the installers would have caused it just from sliding a tile in/out below it). So I’m inclined to think this is coincidence rather than water getting in and tracking all the way down to the window - but I mention it just in case it’s not a red herring. A pic is attached but sorry it’s not good as I only found this forum now it’s dark. I can take one tomorrow in the light if that helps.

Oh and one last bit of info. I was previously leaving the vent on the velux open as I thought that would be better for condensation but Velux’s website says not to do that. Although I can’t see how condensation would get from the vent to the damp patch.

Anyway - after all that background (sorry but I thought it all might help) - my question is, does the patch in the attached picture seem plausible to be a condensation issue that could be managed with a dehumidifier - or is this obviously a proper leak?

Thanks in advance.
Attachments
76AA2799-7A34-41EA-87D4-A8965E59C21E.jpeg
The missing tile segment
D6CD0D52-42E7-4371-8172-6AFB12F32A25.jpeg
The damp patch
py9mrg
Rank: Labourer
Progress to next rank:
75%
Posts: 4
Joined: Sun Dec 27, 2020 7:57 pm


Sponsor

DIY asbestos test kits

Postby stoneyboy » Sun Dec 27, 2020 11:23 pm

Hi py9mrg
If you get a lot of condensation on the inside of the glass this could run down the window an onto this corner. It is more likely to be defective workmanship to the flashing and underfelt on the bottom corner of the velux frame.
Probably worth removing a few of the lower tiles to see if a waterproof join has been made.
Regards S
stoneyboy
Rank: Project Manager
Posts: 4052
Joined: Wed Dec 10, 2008 6:44 pm


Postby py9mrg » Mon Dec 28, 2020 8:36 am

Hello stoneyboy,

(I already replied I thought, but it’s not there so sorry if you get this twice!)

I’m pretty sure it’s not dripping from the glass as the frame of the actual window section seems bone dry. But when I feel the lower left section of the main frame, that can be a little moist to the touch on cold mornings. But it doesn’t look enough to create an actual drip, so I think maybe it is a leak as you suggest. It was a velux approved specialist that fitted the window so I hoped it would be done right!

One other thing, I am able to get in the roof section below the window and look back up towards the bottom of it. I can’t see the wooden structure they fit the velux frame into, but I can see a rafter that must run closely parallel to what would be the bottom of the wooden structure and there’s no evidence of any moisture.

I guess I’ll get someone in to look as I’m not brave enough to remove tiles - and wouldn’t really know what I am looking for.

Thanks for your advice.
py9mrg
Rank: Labourer
Progress to next rank:
75%
Posts: 4
Joined: Sun Dec 27, 2020 7:57 pm


Postby py9mrg » Thu Dec 31, 2020 6:04 pm

stoneyboy wrote:Hi py9mrg
If you get a lot of condensation on the inside of the glass this could run down the window an onto this corner. It is more likely to be defective workmanship to the flashing and underfelt on the bottom corner of the velux frame.
Probably worth removing a few of the lower tiles to see if a waterproof join has been made.
Regards S


Hello again,

I haven’t been brave enough to remove any tiles but took some pictures of the relevant side, top and bottom corners of the window (you can see the location of the tile with the missing channel, and up inside too). Don’t know if there’s anything obvious you could see from these?
Attachments
m_IMG_3095.jpg
m_IMG_3096.jpg
m_IMG_3100.jpg
m_IMG_3106.jpg
m_IMG_3110.jpg
py9mrg
Rank: Labourer
Progress to next rank:
75%
Posts: 4
Joined: Sun Dec 27, 2020 7:57 pm


Postby stoneyboy » Fri Jan 01, 2021 10:52 pm

Hi py9mrg
The installation looks fine and no obvious defects.
The issue may be with the underslaters felt around the opening made when the windows were installed. The only way to check this is to remove tiles around the window and the flashings. Once you get to this stage if a BDX/BFX kit is not fitted it’s probably worth fitting one. Look for the one with the drain channel which fits at the top of the window.
Regards S
stoneyboy
Rank: Project Manager
Posts: 4052
Joined: Wed Dec 10, 2008 6:44 pm


Postby py9mrg » Wed Jan 06, 2021 1:36 pm

Hello again,

I haven’t braved removing any tiles as (I think) installer added the kits you mentioned and also put some expandable foam in too, so I don’t want to risk disrupting that unless I have to. But I actually caught the condensation in the act of dripping. It wasn’t as severe as last time, just a few drips (yet the window had a fair bit but not huge amounts of condensation on it) - so it seems like the polycarbonate coated windows have more of a tendency to drip over the frame even when not that much condensation on the windows. Have got a dehumidifier that has dramatically reduced build up (at most a slight misting in corners now), and will keep a close eye on it next time it rains, but seems like it might have been a particularly bad day for condensation when the temp dropped suddenly in my area. If the problem recurs when it rains then obviously it is a leak after all and I’ll follow your advice above - I really appreciate how clear and thorough it is! Thanks again for time and insight.
py9mrg
Rank: Labourer
Progress to next rank:
75%
Posts: 4
Joined: Sun Dec 27, 2020 7:57 pm


Postby stoneyboy » Wed Jan 06, 2021 9:36 pm

Hi py9mrg
Thanks for the update.
Regards S
stoneyboy
Rank: Project Manager
Posts: 4052
Joined: Wed Dec 10, 2008 6:44 pm



Display posts from previous
Sort by
Order by



  • DIY How to Project Guides
  • DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!


 
  • Related Topics