New extension & signs of damp

[rh2205]

Extension is 6 months old. Just noticed this on one of the window reveals, it is the only window not under the eaves we had these annoying velfac windows that have some pretty atrocious interface detailing so I’m guessing it’s got something to do with the reveal, how bad does this look and any ideas? Extension is timber framed.

[Olf]

I had the same symptoms with a window that was installed without using any foam around it - just screws and mastic on the sides and top, but not under the sill!. With such professional (FENSA certified) job,  the outside cold could effectively reach all the way to the inner leaf. With low temperatures this time of the year it causes condensation of water vapour and on plasterboard it is just more obvious. Go outside and have a look around detail under the external sill, you might be lucky to have some mastic/silicone but any cracks will allow cold air to circulate freely.

[Mr Punter]

We fitted some Velfac windows on a project 12 years ago and one had a similar issue.  We had fitted them according to the Velfac drawings and details.  In the end, Velfac replaced in at their own expense under guarantee.

 

Their current install drawings look a bit more robust nowadays.

 

The issue is either external weather ingress of condensation.  A picture of the outside may help.  These are often sealed externally with Compriband foam tape.  If so and the gap is fairly wide, you could remove a section and see what is going on.  If there is a large void you could fill it with foam and redo the Compriband.

[rh2205]

So we do have a slight condensation issue on all the windows, probably skimped on ventilation with basic extractors in bathrooms & trickle vents everywhere else which we sometimes open.. as the whole house was refurbed & wrapped in EWI plus additional rafter & internal stud wall insulation that we spent weeks taping it’s probably making condensation more

likely when it drops near freezing … however this is the only one that goes beyond the window pane in terms of a sign of damp but it’s never obviously run from the glass onto the wood frame before so I think it’s more than just window condensation. We have some weird vertical cedral click concrete cladding that made this detailing worse! I will get a ladder up there to see whether it’s obvious but I remember the builders generally being very bemused by such strange interfaces (installing onto a completely prepared reveal). And I do have some vague recollection of discussions around the lintel drip detail on this particular window (it didn’t come up on any of the others), can’t really remember what was said so I hope it’s just the mastic or compriband!!

[Olf]

8 hours ago, rh2205 said:

So we do have a slight condensation issue on all the windows, probably skimped on ventilation

Invest in £10 device that will show relative humidity, that will give you an idea how bad the ventilation is and at what temeperature condensation happens - that is roughly the temperature of the wet patch you see.

With another £30 spent on a decent IR thermometer you can check for cold spots (fancy thermal camera will do it better, but at a price) and it will better pinpoint where the cold gets in.

 

[Marvin]

Put a tissue on the window board and leave over night to see if it's running off the window...

[rh2205]

Oh actually I think we can borrow thermal imaging cameras from the council! Great idea though I suspect it will take a bit of time to get hold of it..

[rh2205]

I’ve requested the council thermal imaging camera & booked onto the free training on how to interpret results, it’s 2hrs long so I’m hoping the content is actually useful, but I don’t recall it being that complicated when I used one on our old house with no training!