Yes I was wondering about that and indeed whether a bit of condensation from
the causes mentioned would be enough to create it.
After all it has to have come from somewhere, and I was thinking another
moisture source from evaporating hot water or somesuch.
Brian

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On Sunday, 12 May 2019 11:52:42 UTC+1, Mathew Newton wrote:

I've just been up into our loft and was horrified to find what appears to
be black mould on the underside of the roof felt:

https://thumbsnap.com/Ijt6WPKP
https://thumbsnap.com/w3zVIJbI

(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
that then (or at any time previously).

The house was built in 2007 and the felt appears to be of the breathable
variety (it looks like a teabag when viewed close-up) however I am
assuming that even a breathable felt can't work miracles if there's
excessive moisture being generated in the house, particularly given how
dirty the felt appears to be on the tile side? There appears to be no
eaves ventilation (hard to tell as it's a 2.5 storey house so the top
bedroom has hipped ceilings which 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
more vegetable steaming than we used to, extra loads of washing, great
house occupation, reduced ventilation to 'keep the baby warm' etc have all
contributed 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
lifestyle 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 looks 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 felt? 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?

Bleach is the stuff to use on mould. When that's not usable I've used copper
sulphate.
Is it mould though?


NT