"cynic" wrote in message
...
On 8 Jan, 19:55, 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

Unless you have foil backed plasterboard or some other vapour proof
barrier moisture will migrate through the ceiling and insulation into
the loft and then condense on the cold underside of the roof.
You might limit the effect by ventilating the roof space but this will
reduce the temperature considerably and if you have loft water tanks
and pipes they may suffer!

Best seal all gaps between rooms and loft inc' ceiling roses and pipe
entries. Have a loft hatch with a seal. Then paint the loft floor with oil
based paint.This will seal enough to prevent water vapour moving from house
into the loft where it meets cold surfaces and condensates. Some paint the
ceiling with oil based paint and mat paint over. This will also keep the
house warmers as hot air is not moving out of the house -you pay for that in
energy bills.