Cavity wall ventilation

[sparkydave in wales]

A friend lives in a house that has a block built extension, the extension was built in the mid 70s, with cavity walls, she is getting some damp/condensation at the top of the walls inside, what I have noticed is that there is no ventilation into the cavity or loft, would adding vents towards the bottom of the wall on the outside, and though the inside leaf of the wall in the loft help?, creating a little air movement feels like a logical improvement to me, but it's not my "specialist" subject

 

[bobasd]

dont vent cavities.
post a photo of the damp signs and a photo of the outside at eaves level.it will maybe help to see if its condensation or penetrating damp.

 

[John D v2.0]

Less likely to be condensation at this time of year. Can you see black mould or just staining? As bob says above don't ventilated the cavity as it's part of your insulated later. It should really be drained belowbelo closed above.
If it's staining on the walls it could just be the felt at the eaves is incomplete. Try lifting a couple of tiles at the bottom to see the condition. It should be continuous fall into the gutter, but often water has pooled and rotted the felt.

 

[^woody^]

Less likely to be condensation at this time of year.

It's still spring, walls are cold, extreme differences between day and night temperatures, and a bit of increased humidity ..... never say never.

 

[John D v2.0]

Always say less likely, then you can get out of any with a caveat. That's the scientists approach