(Note: The white 'strips' are where the felt is overlapped)
I haven't been up there since last summer and I am certain it wasn't like t hat then (or at any time previously).
The house was built in 2007 and the felt appears to be of the breathable va riety (it looks like a teabag when viewed close-up) however I am assuming t hat even a breathable felt can't work miracles if there's excessive moistur e being generated in the house, particularly given how dirty the felt appea rs to be on the tile side? There appears to be no eaves ventilation (hard t o tell as it's a 2.5 storey house so the top bedroom has hipped ceilings wh ich mean the eaves aren't visible from the loft space).
We have a nearly-2yr old toddler and have also been undertaking a fair bit of building work over the last six months and so I think a combination of m ore vegetable steaming than we used to, extra loads of washing, great house occupation, reduced ventilation to 'keep the baby warm' etc have all contr ibuted to an excess of moisture and it has condensed on the cold surface in the loft over the winter months.
If the above is true then I am sure we can remove the cause through lifesty le adjustment, however I am still concerned about the mould that is already present. Should I try and clean/remove it? If so, how and what with? It lo oks like most of the black mould spray cleaners contain bleach (to kill the mould and remove the staining?) and so wondered if this might damage the f elt? Perhaps something without bleach more geared towards mould removal off fabric/furniture? If I just left it (and cured the cause) might some of it disappear anyway?