Condensation in my loft

[geordey]

I recently went up in the loft to get some Xmas things down to find water (condensation) covering the whole of the plastic lining under the tiles. Droplets were dripping down on everything and some things were showing signs that this was not a one off. I have glass fibre insulation, double glazing and cavity wall insulation, the house is pretty warm and it was cold outside. The roof tiles are fine and there are no signs of leaks.

I do not know why this is forming or how to deal with it - any advice welcome.

 

[Mr Winston]

what sort of ventilation do you have

if youve had loft insulation done make sure its not blocking any vents

 

[Lymers]

I've also just started getting this following insulation of the loft, the main offender was the shower and having no vapour membrane . I'm now fitting an extractor fan and putting a vapour barrier over the bathroom. As we live in an old cottage with NO open ventilation I'm also looking at adding some form of retrofittable vents in the roof tiles.
Hope this helps ?

 

[geordey]

I believe I have found the cause. The combi boiler exhaust, installed by the previous owners has its exhaust 1ft from the eaves and a vent hole. It must be this as hot moist air goes straight into the roof space. I will be blocking that vent (there are planty others) and am amazed they never spotted this.

 

[geordey]

I blocked the one vent hole from the combi exhaust into the roof space - the condensation is still there. Intend putting a seal around the loft hatch but am now running short of ideas.

Recap:
- Loft & cavity wall insulation - fitted some years ago by the previous occupants.
- Condensation on black PVC sheeting in roof space (everywhere)
- Dripping down on belongings and the glass fibre insulation covering the plaster board of the ceilings below.

Suggestions welcome.

 

[bikerm4]

when you say condensation on black pvc sheeting, is this the sheeting under the tiles i.e. underfelt or has it been tacked on under the rafters.
A reinforced plastic underfelt called Monarfol used to be used under the tiles in some properties which could cause massive condensation problems , the cure is to fit slate or tile vents to get plenty of ventilation into the loft.

 

[geordey]

Not sure what the sheeting is called but it is underneath the tiles.

The house was built in 1975.

Where is the best place to put vent tiles?

 

[bikerm4]

The reinforced underslating called monarfol is recognised by it being made up of small squares about 12mm square. These are formed by the reinforcing knitted into the plastic underfelt to strengthen it.
Vent tiles should be put at the bottom and top of the roof so air will circulate.usually 3 half a metre up the roof and another 3 half a metre down from the ridge, the number you put in will depend on the size of your roof. This should be done on both sides of the roof

 

[geordey]

Thanks for the quick reply.

I have found some holes above my combi boiler (it was installed in the cupboard where the old expansion tanks was. Old pipes from the now empty tank in the loft ran into the space and when removed the holes were not blocked up - they are now as the cupboard gets warm and this air would be going into the void. I have also added insulation (draught excluder) around the slightly warped loft hatch.

The black PVC (marofil?) is between the tiles and timbers.

I have one layer of fibre insulation in the loft which is around 3 inches deep - not enough? I am considering laying another thicker lot on top.

Feedback welcome.

 

[Nige F]

I believe I have found the cause. The combi boiler exhaust, installed by the previous owners has its exhaust 1ft from the eaves and a vent hole. It must be this as hot moist air goes straight into the roof space. I will be blocking that vent (there are planty others) and am amazed they never spotted this.

But are the others clear thru to the roofspace I`ve seen wi` me own eyes..........continuous soffit vent on outside.inspected inside loft.......sealed right over (On an estate of 200 housing assn. places.all the same )

 

[Joatmojo]

It is a pretty simple task to cure roof-space condesation, as well as other problems that airless, stagnant voids generate - create 'positive' ventilation.

Try googling for 'lapvent' that's an easy way to DIY it.