White stains on felt membrane

[Shaun Tim]

Hi

I was in the loft returning the christmas decors and happened to notice a gathering of white stains on the felt underlay of the slate roof. The roof seems in good nick from the outside. Is this the effect of condensation from inside the loft or could this be a problem with the slates. The stains are only gathering on one side of the pitched roof. Also, and this may be connected, we also have a problem with our gable wall. It's a solid end terrace pebble dashed gable but there is no sign of wetness on the outside, however we have had to take down the wallpaper on the inside, upstairs wall. There are no visible signs of dampness in the loft either. Are these syntoms connected. The roof is not fully ventilated to todays standard and the house was built in the 60's.

Any help would be very much appreciated

Shaun

 

[datarebal]

It might be caused by condensation. if you put your head in the loft does it have a damp smell? do you have a photo? the slate will probably be fine and the staining is internal side of the felt. again any pictures? of the external of the roof....