New Velux triple glazed, frame condensation

[Sparrowhawk]

23 hours ago, Roger440 said:

Ive talked before about air leaks past the seals. Is the actually happening? If so, hopefully that can be adjusted out.

 

I am struggling to get a measure of whether it is or it isn't. I haven't got a blower door made yet so I'm reliant on strong winds in the right direction, and the weather's not been cooperating.

 

It could be a cold spot. The 19th was another cold day and this time I opened the windows. I wanted to see if the condensation stopped at the rubber seal or went up the frame alongside the pivoting bit containing the glass (whatever that is called).

 

At the bottom there was the bigger patch of condensation again. I am satisfied these are cold bridging. Here, the condensation stopped at the line of the rubber seal. All along the rubber seal position was a line of condensation but it didn't extend above the seal. Fair enough.

 

At the top corners the condensation went up further all the way to the external seal (the rubber gasket round the pivoting bit comes at approx 1/3 of the height down the white frame here)

 

There was also frozen condensation further up in the window

 

To me the fact the condensation doesn't stop at the seal says there is an air leak at the top corners. Whether I can make Velux understand that the condensation isn't the problem and what it shows is, I doubt it.

 

 

23 hours ago, Roger440 said:

Is this a cavity or solid walled house? The pics suggest that the lower part of the wall is probably quite cold.

 

It's a cavity walled house. I'm under strict instructions not to post photos of the bedroom in its "lived-in" state, but this room is in the 2001 extension and in cross-section is a triangle with its top point cut off. The roof extends to floor level but they put a little stud wall up to hide the end part (no idea what's behind that). The wall to the left is 2001 cavity, filled with either sheet polystyrene or mineral wool. The wall to the right is the original 1920s external wall, empty cavity.

 

23 hours ago, Roger440 said:

61% at 10 degress isnt a great place to be. Why so cold? If you were at 20deg, the RH would drop away and i doubt you would have a problem. So to some extent they are right.

To get the radiator to work properly in this room you have to turn the radiators off downstairs to force more water upstairs. It gets to 13.5C max atm, and then we don't have the heating on in the morning until one of us goes down to turn it on. We will get this sorted when the new heating system goes in.

 

Velux are right that the condensation should disappear with a lower RH, but to my mind the condensation is not the problem but a symptom of another problem: cold spots and maybe air tightness problems.

[Sparrowhawk]

On 19/01/2023 at 22:46, Radian said:

Could do with a photo showing the velux in context with the reveal and roof but the rafters must be in the region of 175mm? With only 50mm PIR between rafters (none underneath the plasterboard crossing the rafters?) some of the reveal would seem to be flanked by almost direct contact with outside air (assuming ventilated rafters).

Here you go

From the eaves on the en-suite side of the room, it will be 100mm air gap and 50mm PIR, and then plasterboard.

 

But here I would hope there's PIR against the wood forming the window surround. And then more given the depth. I don't want to strip off the plasterboard when other places are far colder but it is on my list for "maybe one day"

[Radian]

4 hours ago, Sparrowhawk said:

But here I would hope there's PIR against the wood forming the window surround

How wide is the window reveal? I'm thinking about the spacing of rafters and if it's between a pair (~550mm) or if it cuts through one (>600mm)

[Sparrowhawk]

On 21/01/2023 at 18:27, Radian said:

How wide is the window reveal? I'm thinking about the spacing of rafters and if it's between a pair (~550mm) or if it cuts through one (>600mm)

The width is 890mm.

 

Measuring up the side of the window reveal is 14cm to the edge of the Velux frame / 18cm to the pivoting window. I am curious what's in there, might have to drill an inspection hole and have a look.