Help, mould appearing in 5 year old house

[CBScotland]

Hi,

im looking for some advice, I recently noticed mould spots appearing in a few rooms of my 5 year old new build house, when I investigated in the loft I found no leaks from the roof but did find a green plastic sheet that looks as if it comes up from all the external walls and then folds under the ceiling joists between the plasterboard and joist, it was between this sheet and plasterboard that I found moisture, what would be causing this and should the plastic sheet be there in the first place, I have attached a few photos that show better than I am describing.

 

thanks in advance

[SuperJohnG]

No photos showing?

[Nickfromwales]

1 hour ago, CBScotland said:

Hi,

im looking for some advice, I recently noticed mould spots appearing in a few rooms of my 5 year old new build house, when I investigated in the loft I found no leaks from the roof but did find a green plastic sheet that looks as if it comes up from all the external walls and then folds under the ceiling joists between the plasterboard and joist, it was between this sheet and plasterboard that I found moisture, what would be causing this and should the plastic sheet be there in the first place, I have attached a few photos that show better than I am describing.

 

thanks in advance

Hi and welcome.

If you need any help uploading images, please ask  IIRC we don't have a restriction on image quality / size etc. 

[CBScotland]

7 hours ago, CBScotland said:

Hi,

im looking for some advice, I recently noticed mould spots appearing in a few rooms of my 5 year old new build house, when I investigated in the loft I found no leaks from the roof but did find a green plastic sheet that looks as if it comes up from all the external walls and then folds under the ceiling joists between the plasterboard and joist, it was between this sheet and plasterboard that I found moisture, what would be causing this and should the plastic sheet be there in the first place, I have attached a few photos that show better than I am describing.

 

thanks in advance

 

[markc]

I’m thinking they are using the visqueen (other membranes are available) for air tightness and moist air is rising through the plasterboard and being trapped.

 

[Radian]

If the loft insulation was sufficient to prevent the plasterboard ceiling from getting cold the condensation wouldn't be forming. Could it be that the extract vent pipe was keeping this area from being properly covered? If you pulled back insulation from another similar location at the eaves would you see the same problem?

[CBScotland]

Thanks for the replies, there is plenty of insulation in the loft and it’s happening in a few areas not just at the extract fan, I’ve found 2 rooms showing the mould and found moisture between the sheet and plasterboard at 3 other areas, how can I prevent this from happening and can I cut away the visqueen and just leave the insulation in place

[MikeGrahamT21]

If its a big developer house it'll still be under warranty for another 5 years, this should be directed at them rather than attempting a fix yourself.

[CBScotland]

I’ve not had the heating on much in the past year as the house is warm enough, but I did find all the trickle vents in the upstairs windows were closed, would this cause it ??

[CBScotland]

2 minutes ago, MikeGrahamT21 said:

If its a big developer house it'll still be under warranty for another 5 years, this should be directed at them rather than attempting a fix yourself.

It’s a Bellway home but they only give you a 2 year warranty, would I be best going to NHBC

[MikeGrahamT21]

Yeah you should have a 10 year NHBC warranty, pretty sure thats standard and required (someone correct me if its not). Mould is a serious issue for human health, so needs a permanent fix which in itself is guaranteed

 

EDIT: Yeah thats right... https://www.bellway.co.uk/buying-with-bellway/warranty-and-insurance-protection

Edited January 11, 2023 by MikeGrahamT21

[ProDave]

15 minutes ago, MikeGrahamT21 said:

Yeah you should have a 10 year NHBC warranty, pretty sure thats standard and required (someone correct me if its not). Mould is a serious issue for human health, so needs a permanent fix which in itself is guaranteed

 

EDIT: Yeah thats right... https://www.bellway.co.uk/buying-with-bellway/warranty-and-insurance-protection

To save your time, stress and anger levels don't bother.  Just search the net for stories of people with real structural problems unable to get satisfaction from NHBC, a few spots of mould in very cold weather, you would just be wasting your time and increasing your stress levels as you bang against a brick wall.

 

I would ask why does the vapour barrier only cover the edge of the ceiling?  So it is a vapour barrier in the wall lapped over the top above the plasterboard.  If done properly you would expect it to either be continued over the whole ceiling, or the edge where it finishes taped to the plasterboard.  As it is any moisture that gets under the membrane is trapped.

 

So I would start with making sure it is dry under what you can see of the membrane then tape the edge to the ceiling. Ideally with air tightness tape, but even something like gorilla tape would be good.  then put the loft insulation back ensuring it is well laid and no bare ceiling is exposed anywhere.  Then see how it goes.

[Radian]

This is why I worry about the practice of using a vapour barrier beneath loft insulation. In theory, if the insulation is doing its job and keeping the ceiling at room temperature, then no condensation should develop between the plasterboard and vapour barrier. But in practice, despite there seemingly being good levels of insulation, any shortcomings with it will lead to this kind of problem.

 

The overlapping membrane may be intended to prevent cold air from the loft descending the wall rather than providing a fungus garden so I would want to understand the build-up before cutting it back.

 

22 minutes ago, ProDave said:

So I would start with making sure it is dry under what you can see of the membrane then tape the edge to the ceiling. Ideally with air tightness tape, but even something like gorilla tape would be good.  then put the loft insulation back ensuring it is well laid and no bare ceiling is exposed anywhere.  Then see how it goes.

 

The problem I see with this suggestion is that there's nothing preventing the build-up of vapour coming through the plasterboard which is not foil backed. Sealing with airtightness tape could actually make things worse. The adjustment I would make to this solution would be to trim the membrane back to the end of the plasterboard and seal the junction to the wall plate with Illbruck FM330 Air Seal foam. 

[ProDave]

25 minutes ago, Radian said:

The problem I see with this suggestion is that there's nothing preventing the build-up of vapour coming through the plasterboard which is not foil backed. Sealing with airtightness tape could actually make things worse. The adjustment I would make to this solution would be to trim the membrane back to the end of the plasterboard and seal the junction to the wall plate with Illbruck FM330 Air Seal foam. 

Yes this is just symptomatic of the way mass market builders throw things together with no proper thought or understanding of the details.  What's the chances the top of the wall is open to the loft to let cold air down, the classic plasterboard tent?

 

Sadly the OP is thinking a 5 year old house will be "built properly"  Penny pinching and not even using foil backed plasterboard for the ceiling about sums up the level of understanding that went into this build.

 

I guess it is going to be a try it and see solution.  Start by taping the joint, see if the problem goes away.  If it does not, or gets worse,  cut down both sides of the membrane close to but not touching the joists (so you can undo this trial if needed) and roll the membrane up back as far as you can to expose that ceiling and see how that goes.

[Radian]

40 minutes ago, ProDave said:

What's the chances the top of the wall is open to the loft to let cold air down, the classic plasterboard tent?

Quite high. The vertical membrane looks to be folded over at the junction between plasterboard and wall plate suggesting that the vapour barrier is directly behind the vertical plasterboard in the rooms below. If the overlap is an attempt to prevent cold air getting down behind the vertical plasterboard it fails as there's nothing sealing it to the wall plate. I.e. it can't fold over in both directions. 

[Mr Punter]

2 hours ago, CBScotland said:

I did find all the trickle vents in the upstairs windows were closed, would this cause it

 

Possibly a factor.  If you apply a coat of vinyl emulsion to the ceiling it will lower the amount of vapour that passes through the plasterboard and may help resolve the issue.

[Radian]

1 hour ago, Mr Punter said:

 

Possibly a factor.  If you apply a coat of vinyl emulsion to the ceiling it will lower the amount of vapour that passes through the plasterboard and may help resolve the issue.

Especially in the bathroom(s). I'd apply more than one coat.