Currently boarding out the attic. I have been monitoring the humidity up there for over a year and it is constantly 85 - 95% year round with damp underneath the slates as in the photo, so I’m concerned this will shorten the lifespan of the timbers. The roof is simple imitation cement tiles, no membrane, no air vents, just airflow through the eaves as standard (eaves are not blocked, but airflow is slow at best). I’ve looked at getting ridge vents, tile vents and even velux windows installed to increase airflow, but could I just not knock out one of the bricks in the attic chimney and fit an airbrick? The chimney is patent, and there is very good airflow from the redundant fireplace in the lounge. Like most attics the mortar is soft as standard so removing a brick wont be difficult. Is there any reason why this would be a bad idea?