Hi,

I have a one bedroom flat built in the early 1970s that is rented to
the tenant. I think the construction is a concrete “frame” with “coal
dust” brieze block internal walls and outer brick facing.

The flat is double glazed (uPVC), gas centrally heated (balanced flue
(?) combi boiler) and carpeted.

On an outer wall in a bedroom mould has appeared twice in the past
couple of years. The mould appears in the area behind and adjacent to
some lined curtains both on an externally facing wall and the adjacent
internal wall. I have in the past cleared the mould using bleach,
washed the walls and reemulsioned. I guessed the mould would reappear
and it has.

I am going to buy a De Longhi dehumidifier today. This device gets
decent reviews for its quiet operation and effective drying ability.
All that I have read on this topic tells me

Humidity/moisture in the air Meets cold surface condensation
mould

Now, I don't have control over the tenant's life-style and leaving
windows open all day isn't practical in a downstairs flat. The trickle
vents are open – so I suppose some would argue that dehumidifying is
absolutely pointless as the air will just get replaced. However, my
thinking goes like this. If I can create a local “dry spot” where the
mould forms then I will be tackling the problem where it occurs.
Basically I'm taking a £100 gamble on the dehumidifier to improve the
situation for the tenant and I can't make the situation worse.

Longer term I'm thinking about cavity wall insulation. The idea being
to try to stop the external wall being (so) cold therefore stop the
condensation. A useful by-product would be lower heating bills -
although the finances probably wouldn't pay back during the life-time
of the building. The aim would be to improve the conditions in the
building and lower the risk of mould on the inside of external walls.

So – after all that – does anyone know for the building type I have
described if cavity wall insulation can be installed and whether there
would be any benefit from doing so? I know I would have to get the
freeholder on board too. I'm just trying to understand if the
insulation is a possible (allbeit slightly expensive) solution to the
mould problem.

Regards

Clive