New extension - leaking roof or condensation?

[DIYBrit]

I've been having problems with condensation in my new extension, which was internally plastered about 3 weeks ago. Currently there's no heating in there and I'm due to get a radiator fitted.

There's a persistant dark patch to the front, just above the sliding patio door. Recently, this has been spreading underneath (see pictures). In the past week or so, two new dark patches have also appeared. Could this be melting snow?

The builders reckon this is due to condensation (I cannot deny the condenstion issue). However, I'm concerned there's an issue with the roof/fascia/soffit. I've started running an electric heater in there (costly, it's a shame its winter), to deal with the condensation from the drying plaster.

Is this due to condensation or could it also be due to a leaking roof?

 

[Murdochcat]

If there is no heating and the plaster is not completely dry have you got windows open ?

All the moisture needs to get out of the room

 

[DAZB]

It looks like that you have no ridge on the left side of the roof and that is above where the internal problem is so may be getting water in at that point and somehow finding a way to get past the felt. Would be worth just removing the tiles in that area as it will be fairly obvious if you have a roof issue.

 

[Alastairreid]

It looks like that you have no ridge on the left side of the roof.

Mono ridge.
Did the builders install cavity trays?

 

[datarebal]

No trays, and or bad seal around upstairs window

 

[DAZB]

Trays or no trays water is still entering under the tiles so lifting them will show much more also the window isn't in direct line of where the damp is so less likely to be the cause.

 

[DIYBrit]

If there is no heating and the plaster is not completely dry have you got windows open ?

All the moisture needs to get out of the room

Good point - I've started leaving an electric heater on in the extension and opening the side windows to let the moisture out.

 

[DIYBrit]

It looks like that you have no ridge on the left side of the roof and that is above where the internal problem is so may be getting water in at that point and somehow finding a way to get past the felt. Would be worth just removing the tiles in that area as it will be fairly obvious if you have a roof issue.

As Alastair mentioned: it's got a mono ridge tile on the top, left hand side of the roof.

I noticed where the tile joins the brick, there is some sort of black, tar like sealant. I wonder if this sealant also needs applying between each mono ridge? Bear in mind this is only an assumption, as I'm not a roofing professional. I've attached pictures of this tile.

 

[DIYBrit]

Mono ridge.
Did the builders install cavity trays?

I'm not sure if the builders installed cavity trays. I'll mention it to them.

 

[foxhole]

Are all gutters clear?

 

[Alastairreid]

There should be a gasket between the ridges.