Condensation in ceiling caused by extractor fan?

[Olivia04]

Hi,
Our extension has a low pitch roof, around 14 degrees.
The roofer fitted a ventilation system at the top (under the flashing I think) and bottom to make sure we had good air flow.
The past few weeks water marks have been appearing on the ceiling.
It’s only when it goes cold, not after it’s been raining so we’re pretty sure it’s condensation. The water is definitely coming through the plasterboard, not forming on the ceiling.
The water is appearing in one place only, right by our extractor fan. Is it possible this is causing the problem? I don’t think the ducting was insulated when it was put in.
The roofer is just finishing his current job before he comes back.
Just wondering if anyone had any idea what could be causing it.
I’ve attached a photo, the hole is where it was so wet my husband accidentally put his finger through the plaster.
thanks

 

[opps]

Are you sure that you don't have a leak in the roof?

Is the extractor fan on an exterior wall. If not, do you know why it is in the wall and not the ceiling? Off hand, I can't see how the ducting could run up from the fan and in to the ceiling void.

The fact that your hubby was able to push his finger through the plasterboard means that you will need to cut in a new section of plasterboard. I would be tempted to cut away a section and see if the underside of the roof is wet.

 

[Olivia04]

Hi,
Well not 100% sure. But it dried out on Saturday and then was wet again yesterday and even more so today. But we’ve had no rain.
The fan is on an internal wall, with the ducting going through the utility roof space (which has a flat ceiling room for the ducting in the roof space) and then out through the eaves.
Oh crikey really? I thought it would be ok once dried out! ‍
thanks

 

[opps]

Hi Olivia,

I can't get my head around how the ducting works. If your is a Victorian house (for example) the old exterior (now interior wall) would have been 9" thick (excluding plaster). A brick is 4.5 inches deep. Most fans, at a guess are protrude 4 inches deep in to the wall. If the builder used a low profile rectangular ducting, he would have needed to go from the round fitting on the back of the fan to an interface that allows him to use rectangular ducting. That would have been an extremely deep chase.

Why is it on a wall and not in the ceiling? Is this a bathroom or the kitchen?

It is a tad outside of my comfort area but you get cold roofs and warm roofs. With a cold roof, you have insulation directly above the plasterboard. I suspect that you have a cold roof with any ducting sitting on the insulation. I cannot see that air running through the ducting would be sufficient to completely soak a ceiling.

It might be possible that the builder used rectangular ducting on the wall and where it meets the horizontal section it is leaking. I have no idea how moist the air leaving the room is though. Either way, the plasterboard needs to be cut back to the joists, only then will you be able to see what is happening. Typically, one cuts the plasterboard half way along the two closest celling joists and patches in a new bit of plaster. It isn't a biggie.

 

[Olivia04]

Sorry I’ve not been very clear. The wall is a stud wall. It’s in the kitchen. We had it put in the wall as there was no room above the ceiling for the ducting due to the sloped ceiling.
Yes it’s a cold roof.
Although I’ve just found another spot about 1 meter away so we must have some condensation problem up there, not being caused by the extractor fan.
The roofers put in ventilation at the top and bottom of the roof, is there anything else they can do to ventilate such a low pitch roof?
thanks

 

[^woody^]

Any images of the wider ceiling area and the roof from outside to show the fan in context, and the outlet terminal position. Wide angle not closeups

 

[catlad]

Vapour barrier and foil backed plasterboard would help

 

[Olivia04]

So this is the ceiling this morning, even wetter than yesterday but again we’ve had no rain. There is another patch of water that has appeared which I’ve circled. Problem is the roofer said 2 weeks ago he’ll come back when he’s finished his job, but in the meantime our ceiling is getting wetter and wetter
I’m thinking of maybe pulling out the spotlight to see if it’s wet there too.

also photo of the roof, I’ve circled whereabouts the fan is.
We’ve had a terrible time with this roof. The builder did a crap job, it must have leaked around 11 times in 2 years. We then got a roofer to come and take it all off and redo it back in the summer. It’s been absolutely fine until now.

 

[catlad]

Spotlights say it all!

 

[Olivia04]

You think the hot air is rising up through the gap in the spots?
The rest of the ceiling is completely dry and we’ve got 8 spotlights.

 

[Olivia04]

Ok, so my husband has been into the roof void where the extractor fan ducting is, above the utility. It’s completely dry up there. And the stud wall goes all the way to the felt. So I don’t see how any heat from the extractor duct could pass into the kitchen roof.

So it’s just condensation on the kitchen roof, and it’s from the spotlights and heat going up what can we do about this? I know they left a gap in the insulation for the spots to be fitted, but if we were to remove the spots there’s no way to fill this gap in insulation unless we go via the roof.
The roof was completely replaced in the summer so don’t really want to take it up again in areas to put in insulation.
Are there any other options?
Thanks

 

[^woody^]

If that's a hip, where does that fan extract to?

Sealed spotlights - fire rated or bathroom rated

Its a bit hard to see from the angle but the tile lap looks a bit short. If so, I wonder if its a roof issue?

 

[Olivia04]

The ducting goes through the utility roof void and out the soffit.
We had the roof redone in the summer as the builder had done the tile lap at about 7.5cm, the new roofer redid it and added another 3 rows of tiles so I’d hope it wasn’t short again!
Plus it only happens in cold weather not in rain.

 

[foxhole]

Is the ducting flexible ? If it’s holed it will dump condensation on your ceiling.

 

[Olivia04]

Hi yea it is.
No, my husband went up into the utility void where the ducting is, that part of the roof is bone dry.
We’ll look at some sealed spots and hopefully that will help.