Damp - Roofing flaw?

This is my first post and has been prompted by a common problem of damp. I first noticed that water was starting to leak onto the ceiling and wall of one bedroom at the outside facing wall. On investigation in the loft I notice some of the felt is cracked and shoddy at the edge and is likely to need patching/repairing. I then went on to find damp in another bedroom in a fitted wardrobe that backs on to an outside wall so I called the builder I trust to come and take a look.

He advised that the bitumen type felt used in properties from the late 70's when ours was built was no good and that I would be best having the whole roof re-felted which is very expensive.

I've since done some reading and found that lack of ventilation in wardrobes facing an exterior wall is common and that they simply need venting. A little more reading and then the large open top fish tank in the back bedroom and the fact that there isn't an extractor in the bathroom yet just seems to add weight to the condensation theory.

Whilst I know that the first issue will need fixing I wanted to ask some advice on whether the builder's verdict is right about the type of felt used and if it is something I should consider in the future. Assuming the condensation theory sounds right and the fact I know the facias and soffits will need replacing over the course of the next 12 months, does the whole roof need to be re-done?

Any advice welcome, thanks.

you dont need a new roof because the felt at the eaves has perished! plenty of roofs have no underfelt, if your tiles or slates are in a decent condition then you dont need a new roof.

you can get over facia trays fitted when you get your roofline works done which will counter the damaged edges of the felt.
soffit or over facia vent can be installed as well which should help alleviate any condensation issues you have.

havent heard of underslating felt being of an inferior quality from the 70s as opposed to similar products used today, though its normally breathable membrane which is used nowadays.

Thanks for the response. I have done a little more checking tonight and I don't think it is condensation any more.

I've got hold of a damp meter which has a scale of 10-16% Green 16-20% Yellow and 20-28% Red. The kitchen and living room both read <10% whereas the room that has the definite leak has readings in the red on the affected and adjoining walls. The other walls in that room and all other rooms vary but are all in the yellow with the outside walls tending to be worse.

For info the whole of the upstairs reads RH of 65-70% and downstairs is about 50%

Does this mean moisture getting in under the eaves all the way round, or just in the leaky room leading to condensation elsewhere? Does it sound feasible for the water to come in between the guttering, rooflines and felt?