Condensation in loft - wall extractor poss cause?

[shorn]

Hi,

Like many others I'm sure, I've gone into the loft to fetch the xmas decs and found condensation on the inside of one side of the roof. (We only moved in a year ago)

It's only on one side, but it's the side the has the most heating (stairs on the other side) and I'm trying to determine what's the cause (or variety of reasons).

Theres a lot of insulation up there. In some places 2/3 layers of insulation. Worth removing some?
I've checked the ventialtion from the soffits. The insulation is back from the eaves and there is a plastic vent at the bottom of the eaves so I guess this helps. Checked the two soil pipe vents and they seem fine. Soffits have a continual grid all along them.

Our ensuite is the side that has the condensation and it has a wall extractor. However I've just checked it and it appears as though that the extractor comes out just below the soffit.
I'm wondering if the air from the extractor is being forced back up into the loft?

Other than adding the plastic lap vents, not sure what else to look for?

 

[JohnD]

step into my time machine...

https://www.diynot.com/diy/threads/condensation-in-loft-answers.160032/

 

[shorn]

I've read that one. Helpful, but doesn't quite answer the specific question of the wall extractor and whether that would be causing an issue though.

 

[Why Not Indeed]

It's only on one side, but it's the side the has the most heating (stairs on the other side) and I'm trying to determine what's the cause (or variety of reasons).

Which side gets the most sun? My roof also has more obvious signs of condensation on one pitch than the other. It's the side that faces slightly more north, and is shaded by a tree for 6 months of the year.

I'm wondering if the air from the extractor is being forced back up into the loft?

Inevitably, some will, when the wind is in the right direction. But it's not going to be a significant proportion of it.

 

[JohnD]

I'm wondering if the air from the extractor is being forced back up into the loft?

Other than adding the plastic lap vents, not sure what else to look for?

Have a look on a cold frosty morning when you can see the "steam." You could possibly add an extension or directional vent.

Open up the eaves ventilation if it is obstructed by insulation. You can cut it to a bevel with a breadknife. You should be able to see daylight on (at least) two sides of the loft and this will give you a crossflow of air.

If you don't drape wet washing in your house; use an effective bathroom extractor; have no plumbing defects; and no holes in the ceiling, eaves ventilation is usually enough. You can sit in the loft with the hatch closed while someone wafts a joss stick underneath and detect any passage of air from the house.

Some bathroom fans are ineffective. Show us a pic of yours, and the duct, please. Clean out any fluff obstructions from the grilles. Does your vent have the rattly plastic flaps like a ventian blind? I think a cowl vent is better.

 

[Leofric]

Show us a pic of yours

- cheeky

 

[datarebal]

dont reduce the insulation it will add to the problem.
better to increase.
you need to reduce the amount of warm moist air entering the loft space.
is the extractor actually connected to the outside ?

 

[Mottie]

Aha! I sometimes get some condensation in my loft. I have the original 60’s cement/waffle type of air vent on my outside wall and when I fitted a bathroom extractor I just fitted it on the inside of that and left it. No vent pipe/duct, I just assumed it would blow the air through the vent. I have cavity walls so I am assuming that some of the steam from the bathroom is going up through the cavity and into the loft. Also, my loft is well insulated but my loft hatch isn’t. Should it be?

 

[HERTS P&D]

Yes:

https://www.google.com/search?q=ins...WnQ0EAHa82AxMQ_AUoAnoECA8QBA&biw=1280&bih=578

Andy

 

[JohnD]

dont reduce the insulation it will add to the problem.
better to increase.

If excessive insulation has been flopped into the eaves obstructing the airflow, it must be trimmed to allow fresh air to enter and replace the damp air.

 

[foxhole]

Simply opening the loft hatch could allow enough moist air into the loft to cause condensation.

 

[datarebal]

excessive insulation

You cant have excessive.. Obviously you need clear ventilation above the insulation.

 

[JohnD]

Yes you can.

If excessive insulation has been flopped into the eaves obstructing the airflow...

 

[shorn]

Thanks for responses. So yesterday made sure that the insulation was pulled right back from the eaves. It had these plastic eaves vents which I guess allowed some airflow but I figured pulling it back further wouldn't hurt. There was a couple a places where it looked like mice might have been (chewed up insulation down in the soffit) I'm going to try and clear that soon.

I popped up today, and it looks better. My concern though is that the damp insulation isn't helping things at the moment and I probably have to remove that.

 

[Leofric]

No vent pipe/duct, I just assumed it would blow the air through the vent. I have cavity walls so I am assuming that some of the steam from the bathroom is going up through the cavity and into the loft.

As far as that goes , the fan obviously should be ducted through the wall to outside air, but even discharging into the wall cavity moist air shouldn't find its way into the loft because the top of the cavity should be closed.