Black mould in loft with Drimaster

MeandO

I've posted on the house buying forum but someone suggested this may be a better board for the issue.
The survey on a house I am purchasing has come back with black mould on the underside of the white felt and on the wooden rafters in the attic. The house also has a drimaster system fitted in the attic. The surveyor has said this could be the cause of the problem, pushing warm moist air into the loft, but I thought they did the opposite? 

Does anyone have any knowledge or experience of this please and could offer any advice? I can get extra vents etc added but would I need to get rid of all the mould stained felt too and scrub the mould off the rafters or is that a job for professionals?
I’m concerned as to the health implications of the mould for myself and my child if I do proceed with the sale and whether to proceed at all really. 

MeandO

Anyone? Any help or opinion would be gratefully received.

tacpot12

I added a comment to your original thread, but these photos are useful. The membrane that is covering the roof doesn't have any sort of logo or markings on it, so it's not easy to confirm that it is a breathable membrane - you refer to it as "felt", but have you touched it and confirmed that it is breathable? If some cowboy roofer has just used polythene, this isn't breathable, so moisture rising from the house will get trapped in the loft causing the mould.

If the problem is being caused by the membrane not being breathable, the Drimaster won't prevent the mould even if it is installed correctly. This is because the Drimaster will be sucking in air from wherever it can, and this is likely to be around the eaves, so the fresh air will travel horizontally across the loft to the Drimaster, and the air higher up will never get stirred up. If this is the problem, its can be solved by installing three vent tiles at the ridge and cutting away the membrane under the ridge tiles. This will allow the Dirmaster to put air from both the ridge and the eaves and this should prevent the build up of any moisture. (Moisture in the loft will be pumped into the house and out through the trickle vents that are need for the Drimaster to function - the windows in the house do have trickle vents, don't they?)

MeandO

Thank you tacpot12, that’s really helpful.
I haven’t been in the attic myself, but the surveyor has described it as ‘felt’ so I’m hoping he is correct in his description. The roof is around 3 years old if that helps in any way.

Yes, there are trickle vents on the windows which are also only a few years old and in good condition.  

The neighbouring houses seem to have vents on the roof, whereas this one doesn’t which probably hints at the issue. 

Would you happen to know whether I would then need to do anything with the mould growth, such as getting it removed or killed off somehow? 

Would the mould have damaged the timbers in any way?