Andy: Hello. I have had a good look and have done some tests on the mould in your spare bedroom upstairs and in the dinign room.
Betty: Hello Andy. Thank you for that, what are your thoughts? 
Andy: I think it is caused by condensation, as most of the moist settles on and around the windows.
Betty: Why is that?
Andy: Those are the coldest areas and therefore where the moist in the warm air turns into water. On the windows its just water, on the walls the moist will allow mould to grow.
Betty: So why is it all over the spare room walls, and all around the dining room? but not in other rooms?
Andy: Probably because they have external walls which are cooler than internal walls.
Betty: so why only that bedroom and not the other ones?
Andy: I guess those rooms are most effected as the spare room is next to the bathroom and the dining room next to the kitchen.
Betty: But why isnt there mould on the kitchen and bathroom itself then?
Andy: I think that is because the kitchen doesn't have external walls and the bathroom has only one external wall and a fan in it. The difference when i measured it between internal wall and external wall is about 4 degrees.  
Betty: Does that mean we need new double glazed windows or new wall insulation?
Andy: Not necessarily. that would make a little difference but would still leave you with moist air in the house, so it would just settle somewhere else.  
Betty: So what would you recommend?
Andy: I would install a fan system, or PIV system, which would circulate air to dilute and take some moisture out of the air. It would be installed in your loft and be on continuously during day and night. 
Betty: That sounds good. would that be sufficient? 
Andy: If you buy a decent size it will be, but you would also need to treat your walls to get rid of the current mould. That will not go away by itself.
Betty: OK, is this something your company can help with?
Andy: It is indeed, we can repaint as well if you want. 
Betty: Good point. Could you please send me a detailed quote for the work via email?
Andy: Of course, I will have that done by Friday. 
Betty: That would be great. And again, thanks for today!
Andy: No problem, speak soon.
Betty's house has mould due to condensation. Andy will send her a quote for the work needed by Friday.