"Cash" wrote in message
...
Fred wrote:
Hi,

I went into our loft to put the Christmas tree away and the rafters
were wet and some of the cardboard boxes up there were damp. At first
I wondered whether some of the snow had melted and leaked through an
iffy ridge tile but I've been told it is likely to be condensation.
I'm puzzled how the warm air gets up there because there's a good ten
inches or so of insulation (rolls). I've been told that once the cold
spell goes everything will return to normal. I am concerned about the
timber getting wet and all the boxes (and presumably their contents)
getting soggy. Is it likely to just be condensation and nothing worse,
and is there anything I can do to limit it? Would wedging slabs of
insulation between the rafters help?

TIA

Fred,

It's interstitial condensation - and I've got the very same problem - and
in my case, it's caused mostly by the steam from the bathroom that seems
to find its way into the well insulated attic through various nooks and
crannies [1] leaving tiny globules of frozen moisture [2] hanging on the
underside of the roofing felt.

Normally this steam is vented from the attic with the airflow through the
roof from the westerly winds that occur at this time of the year, but
these winds have changed direction or stopped for fairly long periods
leaving the moisture to collect - and because of the insulation, there is
no heat in the attic now to simply dry it.

As a matter of interest, this situation has only occurred since we had the
cavity and loft insulation installed about three years ago in a
traditionally-built house of the mid-1970's (with absolutely no loft
insulation installed at the time).

[1] I cannot persuade SWMBO to have a bath with the bathroom window
slightly open to vent the steam for the life of me - and I've tried for
many a year, but still cannot 'educate' here. Please don't show her this
post or I'll be making my own breakfast tomorrow. LOL

Seal up bathroom and paint loft floor over bathroom with oil based
paint.Then observe.