plastic cover in loft - pics attached

happypie

Hi,
I have some part of loft roof covered in plastic done by previous owner. I am wondering why its done? and only partially?
Should i remove it so rafters can get some air?
I see at least one of the rafters getting very bad with mold and starting to crack. I am thinking to apply Sika wood treatment on it. Please suggest if its right thing to do or what else i should do?

I am attaching few pics. Thanks.

https://ibb.co/tB4xds8
https://ibb.co/TYwDF7K
https://ibb.co/rfX274d
https://ibb.co/w6t983f

FreeBear

The previous owner may have fitted the plastic sheeting to reduce draughts. However, it has ruined the ventilation of the roof space... I'd suggest removing all of it and keep an eye on the mold that has developed.

akira181

Who knows why the previous owner done it (a cheap cowboy attempt at insulation or preventing dirt from the roof felt/tiles falling onto their stuff in the loft?) but I can't see polythene sheets with a square cut out it providing enough airflow to prevent condensation and moisture issues. I'd expect that to be the cause of the mould and any rot that you may have.

I would remove all of it and treating the wood can't hurt. If the sheeting needs to be replaced, best to use a breathable vapour barrier sheet of some sort (leaving a good portion at the top and bottom exposed) or better yet, a proper roofing insulating foil.

Aylesbury_Duck

FreeBear wrote: »

The previous owner may have fitted the plastic sheeting to reduce draughts. However, it has ruined the ventilation of the roof space... I'd suggest removing all of it and keep an eye on the mold that has developed.

I would follow this advice. No point treating anything just yet before you understand exactly what's going on.

I would add to this advice: Make sure the loft is otherwise well-ventilated. If the previous occupant put those sheets up to stop draughts, perhaps they also blocked the air bricks? Also, check that insulation hasn't been laid right up into the edges, thereby blocking airflow through the soffits. In my old house I got bad condensation in the loft because the house was oriented in a direction that it got very little airflow through the loft, so I had grills and vents installed in the soffits. In my current house, the loft is nice and breezy on a windy day and there is no problem at all.

Antispam

I would remove it bad for the roof as it will sweat and the roof will rot eventually. You need a breathable membrane. I see mould has already appeared white marks. i CLEAN THAT UP WITH FUNGICIDE (OOPS CAPS ON)

Davesnave

There's no need to be alarmed; the roof timbers look relatively modern, so will be treated timber and a bit of surface mould won't have harmed them.

Once the poly is removed you may find out more, but it's meant to be breezy up there, as the insulation under the loft flooring should be keeping you warm. Is there enough of it? Ideally, should be about 27cm deep.

happypie

insulation is about 300mm (3 layers of insulation wool) as its done recently.
that's relief to hear that.
i am going to remove plastic at the earliest and check status of wood.
thanks everyone.

Mistral001

Davesnave wrote: »

There's no need to be alarmed; the roof timbers look relatively modern, so will be treated timber and a bit of surface mould won't have harmed them.

Once the poly is removed you may find out more, but it's meant to be breezy up there, as the insulation under the loft flooring should be keeping you warm. Is there enough of it? Ideally, should be about 27cm deep.

Dave 9 times out of 10 there would not be a problem, but I have seen signs of wet rot in rafters of a house only three years old. The eaves ventilation was totally blocked by the people who installed the insulation. I visited it in February on a frosty day and the rafters had large droplets of condensation on them. The source of the moisture was a break in the ceiling vapour barrier at the wall between the ensuite and the bedroom.

Norman_Castle

I had similar mould on rafters after blocking a hole between mine and neighbours loft. Unblocked the hole and the mould has gone.

Davesnave

Mistral001 wrote: »

Dave 9 times out of 10 there would not be a problem, but I have seen signs of wet rot in rafters of a house only three years old.

Yes, but the OP's timbers look OK in the picture. Some people on here take a very pessimistic view.
If the OP finds any wet rot when they remove the plastic they will need to deal with it. As I said, "When you remove the plastic you may find out more...."